Urry D.W. (Ed.) What Sustains Life? : Consilient Mechanisms for Protein-Based Machines and Materials

Подождите немного. Документ загружается.

8.4 ATP Synthase: The Twofold Rotary Protein Motor of Oxidative Phosphorylation

415

8.36, on the basis of

AGap,

one would expect the

y-rotor to orient with its most hydrophobic face

away from the two catalytic sites containing

ADP-AIF4 and therefore be directed toward

the pE catalytic site containing ADP-SO4. This

is the orientation of the y-rotor in the structure

in Figure 8.36. Before proceeding to the most

significant aspect of the structures in Figures

8.35 and 8.36, however, additional structures

with different p-subunit occupancies can be

examined to address the consistency of the

expectation that the orientation of hydropho-

bic face of the y-rotor would be toward the least

polar occupancy site.

8.4.4.8 Consistency of Least Apolar-Polar

Repulsion Positioning the Hydrophobic

Face with Three Additional and Different

Binding Site Occupancies

In addition to the structures in Figures 8.30^"*

and 8.36,^^ three more crystal structures of the

Fi-ATPase have been determined by the

Walker group. The first of the three involve

the occupancy states of ATP(A), ATP(B),

ATP(C), ADP(D), P04(E), and ATP(F) for the

protein structure listed in the Protein Data

Bank as Structure File 1H8H.^^ The second of

the three involve the occupancy states of

ANP(A), ANP(B), ANP(C), ADP(D), P04(E),

and ANP(F) where PNP may also be repre-

sented as AMPPNP, that is, a nitrogen replaces

the bridge oxygen of ATP between the p-

and y-phosphates; this structure, shown in

Figure 8.37, is listed in the Protein Data

Bank as Structure File lElQ.^^ The third of

the three additional structures involves occu-

pancy states of ANP(A), ANP(B), ANP(C),

ANP(D), empty(E), and ANP(F) and is listed

in the Protein Data Bank as Structure File

lOHH.^^ In each case the hydrophobic side of

the y-rotor faces the occupancy state of

chain E.

Certainly, the third structure holds the

hydrophobic side of the y-rotor most tena-

ciously at the p-empty catalytic site, even more

so than the structures in Figures 8.30 through

8.34, because all five additional sites are occu-

pied by the ATP equivalent, namely, ANP. The

other two structures depend on the relative

polarities of ADP(D) and P04(E) in their

respective positions of exposure to the y-rotor.

That the P-P04(E) is least polar from the per-

spective of the y-rotor becomes apparent from

the display of the second structure of the three

in Figure 8.37B, where the P-PO4 of chain E is

positioned so as to be sterically obscured from

the y-rotor. Accordingly, consistency holds for

all five structures of the Fi-ATPase; the most

hydrophobic side of the y-rotor is always found

opposite the least polar occupancy site, where

the apolar-polar repulsive free energy of

hydration, AGap, is the least.

8A.4.9 Role of ATP in the a-ATP

Subunits: Triangulation of

Repulsive Forces

When the p-ATP and a-ATP sites are diamet-

rically opposed, as in Figure 8.34C, the appear-

ance read in terms of AGap is that the P-ATP

site expresses slightly more apolar-polar repul-

sion than does the a-ATP site. From the point

of view of the hydrophobic consilient mecha-

nism, this suggests that the exposure of phos-

phates of the a-ATP sites through water to the

y-rotor is greater for the p-ATP sites. Figure

8.38 shows the exposure of the y-rotor to a-

ATP phosphates of chains A, B, and C of the

structures utilized in Figures 8.30 through 8.34.

In each of the a-ATP only a single oxygen of

the y-phosphate can be seen through a small

peephole. While exposure of the a-ATP phos-

phates to the y-rotor could be larger in the

dynamic functional state, this situation is com-

pared with a slightly greater exposure of the

phosphates of the P-ATP site immediately

below and to an analogue of the massively

greater exposure on hydrolysis to form ADP

plus Pi.

By the hydrophobic consilient mechanism,

the a-ATP sites provide a critical role of estab-

lishing a triangulation of repulsive forces that

serves to limit the hydrophobic associations

of the y-rotor. This triangulation of repulsive

forces prevents the occurrence of a frictional

drag on rotor rotation that would seriously

limit motor efficiency.

. Consilient Mechanisms

for

Protein-based Machines

Biology

empty(E)

FIGURE

8.37.

Stereo view

of the

Fi-motor

ATP

synthase

space-filling representation with neutral

residues light gray, aromatic residues black, other

hydrophobic residues gray,

and

charged residues

white.

(A)

Association

of the

p-empty subunit with

the noncatalytic a-ATP subunit

seen from

the

outside. (Prepared using

the

crystallographic results

PO,(E)

of Abrahams

al.^"^

obtained from

the

Protein

Data Bank, Structure File IBMF)

(B)

Interaction

of Pi with

the

p-subunit

association with

the non-

catalytic a-ATP subunit

seen from

the

outside.

(Prepared using the crystallographic results

Braig

al.^^ as

obtained from

the

Protein Data Bank,

Structure File lElQ.)

8.4.4.10 Obscured y-Phosphate of P-ATP

Becomes Full Pi Exposure After

Hydrolysis to Produce Maximal

AGap

for

Repulsive Interaction with the y-Rotor

When looking toward the p-ATP site from the

y-rotor of the structure in Figure 8.30, the only

part

of the

triphosphate observed

is an

oxygen

the

P-phosphate,

shown

Figure

8.39.

Also labeled

are a

number

reference

residues

and a

location, indicated

by the

large

X. The

approximates

the

location where

the

sulfate of ADP-SO4,

analogue

for

ADP-PO4,

appears

in the

very interesting structure

8.4 ATP Synthase: The Twofold Rotary Protein Motor of Oxidative Phosphorylation

417

Menz et al./^ shown in Figure 8.40. In this struc-

ture the SO4 is a more stable analogue for the

hydrolyzed Y-PO4.

The very polar sulfate opens up the structure

to achieve a direct through-water repulsive

interaction with the y-rotor. This observation

provided by the structure in Figure 8.40 has the

most fundamental implications with respect to

the relevance of the hydrophobic consilient

mechanism as describe in Chapter 1.

The most profound and fundamental predic-

tion of the hydrophobic consihent mechanism,

as regards Fi-ATPase function, is that hydroly-

sis to form ADP and Pi provides a water-

mediated burst of apolar-polar repulsion that

would drive the y-rotor in the ATPase mode

aATP(A)

FIGURE

8.38.

Stereo views of each of

the

a-ATP sites

of the Fi-motor of ATP synthase in space-filling rep-

resentation with neutral residues light gray, aromatic

residues black, other hydrophobic residues gray, and

charged residues white. View is from the y-rotor of

the peephole for oxygen of the y-phosphate of the a-

ATP sites for all three sites as defined in Figure 8.31.

aATP( A') shows removal of chain A to expose all of

the ATP analogue (AMPPNP). a-ATP(A), a-

ATP(AO, a-ATP(B), and a-ATP(C) have the over-

lying y-rotor in backbone representation. (Prepared

using the crystallographic results of Abrahams et

al.^"^

as obtained from the Protein Data Bank, Structure

File IBMF)

418

8. Consilient Mechanisms for Protein-based Machines of Biology

P-Pi

Near site

where SO4

appears

FIGURE 8.39. Stereo view of the Fi-motor of ATP

synthase in space-filling representation with neutral

residues Ught gray, aromatic residues black, other

hydrophobic residues gray, and charged residues

white. View is from the y-rotor of the peephole for

oxygen (Oi) of the p-phosphate of P-ATP(F), as

defined in Figure

8.31.

The X shows the approximate

site where emerges the SO4 of ADP-S04(E) of

Figure 8.36, which is taken as the analogue for ADP-

HP04(E). (Prepared using the crystallographic

results of Abrahams et al.^"^ as obtained from the

Protein Data Bank, Structure File IBMF.)

and as regards ATP synthase function that the

state of highest repulsion in the synthesis mode

comes from the face off between the most

hydrophobic face of the y-rotor and the most

polar state of ADP and

Pi.

This severe repulsion

is relieved by reducing the polarity on forma-

tion of

ATP.

A corollary of this prediction is that

the Pi be as fully exposed as possible through

water to the most hydrophobic side of the y-

rotor so that a maximal apolar-polar repulsion

can occur.

If the y-rotor were to be driven by an off-

center application of torque at the point where

the y-rotor enters the (aP)3 structure, such an

exposure of the hydrolyzed phosphate directly

to the y-rotor would seem to have little direct

relevance. On the other hand, with regard to the

hydrophobic consilient mechanism, it is cen-

tral to function. This off-center application of

torque occurs just before the y-rotor goes

from double stranded to single stranded and

explains why the double-stranded rotor con-

8.4 ATP Synthase: The Twofold Rotary Protein Motor of Oxidative Phosphorylation

419

tinues as it does beyond entry into the (aP)3

motor housing.

8.4.4.11 Crystal Structure Evidence for a

Significant AGap Between the ADP-

S04-0ccupied pE-subunit and the

y-rotor

Above,

the predicted hydrophobically asym-

metric rotor was found. Furthermore, the

hydrophobically asymmetric rotor associated

hydrophobically with the (ap)3 housing of the

Fi-motor and was appropriately responsive to

the occupancy states of the nucleotide-binding

sites.

These findings all support the role of the

Gibbs free energy of hydrophobic association,

AGHA,

and of its operative apolar-polar repul-

sive free energy of hydration,

AGap,

in the func-

tion of the Fi-motor. Now by comparison of two

crystal structures, one with the pE-catalytic site

empty and the second with the PE-subunit con-

E399/A

FIGURE

8.40. Stereo view of the Fi-motor of ATP

synthase in space-filling representation with neutral

residues light gray, aromatic residues black, other

hydrophobic residues gray, and charged residues

white. View is of the more stable SO4 in place of the

more polar PO4 (the hydrolyzed y-P of ATP) that

occurs in chain E and is shown in Figure 8.41 with

the overlying y-rotor in gray ribbon representation.

The polar SO4 (encircled) opens up the protein struc-

ture of chain E (when compared with the p-ATP(F)

site in Figure 8.39) to expose the SO4 to the

hydrophobic side of the y-rotor and thereby to

express a large AGap repulsive force through the

intervening waters of Thales. (Prepared using the

crystallographic results of Menz et aP as obtained

from the Protein Data Bank, Structure File 1H8E.)

420

8. Consilient Mechanisms for Protein-based Machines of Biology

taining ADP-SO4, a

AGap

repulsion between the

ADP-S04-containing (JE-subunit and the y-

rotor is found.

To quote from the legend of Figure 5 of Menz

et al./^ "Note that interacting residues in the

PE-

subunit and the y-subunit move in opposite

directions." This movement in opposite direc-

tions of the very polar ADP-S04-containing

PE-

subunit and the hydrophobic side of the y-rotor,

in our view, is a direct result of the AGap repul-

sion between the apolar and polar subunits.The

separation of housing and rotor identifies a

repulsion that introduces an elastic displace-

ment and twist in the y-rotor. Because of the rel-

ative stiffness of the rotor and housing, this

elastic deformation (from otherwise preferred

torsion angles) would have a large elastic

modulus. Accordingly, the reported mean dis-

placement of 2.9 A and twist of up to 20 would

reflect the application of a substantial torque to

the y-rotor. This occurrence again unites the

hydrophobic and elastic consilient mechanisms

in a way that would result in high efficiencies of

energy conversion. The question now becomes

whether or not this applied torque, due to the

AGap

repulsion between the exposed sulfate and

the hydrophobic side of the y-rotor, can predict

the direction of rotation of the Fi-ATPase.

8.4.4.12 Predicted Direction of Rotation

for Fj-ATPase

AGap[sulfate

<->

hydrophobic rotor] provides a

water-mediated off-center "push" on the y-

rotor like an off-center push on a camshaft. The

direction of the repulsion between exposed

sulfate and the hydrophobic side of the y-rotor,

written as AGapfsulfate

<->

hydrophobic rotor],

can be deduced from the structural relation-

ships of Figure

8.41.

The apolar-polar repulsion

between sulfate and y-rotor appUes toward the

lower part of the double-stranded section of

the y-rotor above the amino-terminus of the

y-subunit. As evidenced by the structural

relationships showing the overlay of the y-rotor

on the ADP-S04-containing pE-subunit, the

AGap[sulfate <-> hydrophobic rotor] repul-

sive interaction would provide an impulse to

rotate the y-rotor in a counterclockwise

direction.

8.4.4.13 Demonstrated Direction of

Rotation of the y-rotor

As seen from the landmark study of Noji et

al.^^'^"^

and represented in Figure 8.42, the direc-

tion of rotation for the Fi-ATPase is indeed in

the counterclockwise direction. Thus, the foun-

dation for the hydrophobic and elastic consilient

mechanisms in the function of ATP synthase and

Fj-ATPase becomes increasingly compelling.

8.4.5 Consideration of the Efficiency

and Cooperativities Exhibited by

Fi-ATPase

By analysis of crystal structures, we have just

demonstrated the success of a significant num-

ber of predictions fundamental to the bio-

physics of the hydrophobic and elastic con-

silient mechanisms. Now we address the unique

and fundamental properties of efficiency of

energy conversion and of negative cooperativ-

ity of ATP binding and yet of positive cooper-

ativity of the effect of ATP binding on catalytic

rate.

Can an understanding of these challenging

phenomena exhibited by Fi-ATPase also fall to

the comprehension flowing from the hydropho-

bic consilient mechanism?

8.4.5.1 High Efficiency for Performance

of Mechanical Work

8.4.5.1.1

Near 100% Efficiency of the

Fi-ATPase

With the capacity to attach an actin filament to

the y-rotor and to observe microscopically the

rotation of the actin filament driven by the

Fi-ATPase,^^'^"^ estimates of work performed on

rotation of the actin filament could be esti-

mated as could the energy consumed in the

performance of that work in terms of

the hydrolysis of ATP to form ADP and Pj.

The resulting estimate was remarkably close

to 100%.^^ Such a result stands as a severe

challenge to any proposed mechanism.

Insight comes from considering elastic defor-

mation as a machine for storing energy. By

means of atomic force microscopy in the single-

chain force extension mode, a single chain of

(GVGVP)502 could be observed to exhibit an

8.4 ATP Synthase: The Twofold Rotary Protein Motor of Oxidative Phosphorylation

421

F(F)

FIGURE

8.41. Inside stereo view of chains A, E, and

B and their ligands of the F,-motor of ATP synthase

in space-filling representation with neutral residues

light gray, aromatic residues black, other hydropho-

bic residues gray, and charged residues white and

with the ligands for chains D, C, and F in the fore-

ground. With this perspective, the overlying y-rotor

in gray ribbon representation properly overlays the

catalytic site of the pE-subunit containing the

exposed sulfate. The large repulsive AGap force due

to SO4 apphes a torque just above the amino-

terminal sequence of the y-rotor that would give a

counterclockwise rotation when functioning as the

ATPase. This has analogy to repulsion between like

poles of two magnets that made such an effective

analogue model for the Fi-motor, as presented by

Kinosita et al.^^ The experimentally determined

direction of rotation is counterclockwise, as shown in

Figure 8.42. (Adapted from Urry^^^)

ideal elasticity in which all of the energy

expended in deformation was recovered on

relaxation (see Figure 5A of Urry and Parker^).

On the other hand, when there are adherent

chains that do not sustain the deformation as

occurs with (GVGIP)52o, there occurs a marked

hysteresis; the energy of deformation is not all

recovered on relaxation, as shown in Figure 5B

of Urry and Parker.^ Accordingly, chains that

take up energy during deformation but do not

directly bear and store the force of deformation

cannot return the energy on relaxation. When-

422

8. Consilient Mechanisms for Protein-based Machines of Biology

120°

HIs-tag

Coverslip with Ni-NTA

FIGURE 8.42. Actin filament attached to the y-rotor

by streptavidin and Fi-ATPase fixed on substrate.

ATP drives counter clockwise rotation of the actin

filament in 120°

steps,

which are directly observed by

video microscope.^^'^"* (Reprinted with permission

from H. Noji, "Pharmacia Biotech & Science Prize:

The Rotary Enzyme of the

Cell:

The Rotation of Fi-

ATPase." Science, 282,1844-1845,1998.^^ Copyright

ever this occurs the efficiency of energy conver-

sion becomes limited. Therefore, a mechanism

wherein one protein subunit mechanically

applies a torque to the rotor by physical contact

would seem necessarily and irreversibly to lose

energy into its three-dimensional lattice of chain

segments in a way that cannot be recovered.

8.4.5.1.2

Efficient Use of a Sudden Burst of

Repulsion, as Occurs on Hydrolysis of ATP to

Produce ADP and Pi, Requires Storage in a

Near-ideal Elastic Deformation

On the other hand, when elastic deformation

occurs through a repulsive force mediated by

the solvent, as would be the interpretation of

the consilient mechanism for the elastic defor-

mation reported by Menz et al.,^^ then dissipa-

tion through a lattice of chains would be limited

and a high efficiency could be expected. The

deformation in this case becomes the direct

result of the repulsion and a return to the "equi-

librium" state, which existed prior to the occur-

rence of the repulsive force, would be expected.

Accordingly, on hydrolysis to form ADP^"

Mg^^ plus

HPOj"

the sudden burst of repulsion

due to HPO4" would result in an elastic defor-

mation of the y-rotor and of the associated P-

subunit that would limit torsion angles in a

storage of energy that would be nearly fully re-

covered on the relaxation of rotational motion.

8.4.5.2 Binding of ATP Exhibits Negative

Cooperativity Due to Increases in AGap

with Increasingly Hydrophobic Faces of

the y-Rotor

Negative cooperativity for binding of ATP

would reasonably arise from increasing

hydrophobicity of the three faces of the

8.4 ATP Synthase: The Twofold Rotary Protein Motor of Oxidative Phosphorylation

423

asymmetrically hydrophobic rotor, that is,

an increase in the apolar-polar repulsive free

energy of hydration,

AGap,

with each addition of

ATP.

The first ATP would be expected to bind

adjacent to the most polar face (AGHA ~ +9kcal/

mole),

the second to the essentially neutral face

(AGHA

~ Okcal/mole), and the third opposite

the most hydrophobic face of the y-rotor (AGHA

« -20kcal/mole). The presence of the first ATP

in the most favorable site would leave a less

favorable site for the second ATP binding.

Similarly the presence of the two ATP mole-

cules bound to the more favorable sites would

leave the site with the most repulsion. Thus,

given the structure of the y-rotor with its

hydrophobic asymmetry, negative cooperativity

is the necessary result. While a small contribu-

tion to the negative cooperativity could arise

from direct charge-charge repulsion between

multivalent ATP anions, acting through the

aqueous compartment, this is expected to be

small compared with the increasing apolar-

polar repulsive free energy of hydration,

AGap, that each subsequent ATP molecule

would experience as the result of being con-

fronted with a more hydrophobic side of the

y-rotor.

8.4.5.3 ATP Hydrolytic Rate Exhibits

Positive Cooperativity as Each Additional

Bound ATP Facilitates Hydrophobic

Dissociation of y-Rotor from the Inner

Wall

(ap)3

On the basis of the hydrophobic consilient

mechanism, the three ATP molecules in the

noncatalytic a-subunits are expected to apply a

triangular array of repulsive thrusts that would

limit the viscous drag resulting from hydro-

phobic association between the y-rotor and

the (aP)3 housing of the Fi-motor. Even so,

when there is an empty P-subunit, prominent

hydrophobic association

occurs.

Thus,

as each p-

catalytic site is filled, the hydrophobic associa-

tion would decrease until the binding of ATP to

the third P-catalytic site would dramatically

lower the viscous drag arising from hydropho-

bic association of the (ocp)3 housing of the Fi-

motor with the y-rotor.

8.4.6 Review of Correlations Between

the Hydrophobic Elastic Consihent

Mechanism and the Properties of ATP

Synthase/Fi-ATPase

8.4.6.1 Nine Major Points

of Correlation

Below we list nine major points of correlation

of the ATP synthase/Fi-ATPase. It is not a com-

plete Hsting of the correlations, as there are

many more details that should be included in a

more exhausting consideration. Nonetheless, in

our view the nine points are compelling.

As required for the hydrophobic con-

silient mechanism to be operative for an ATP

synthase/Fi-ATPase protein-based machine,

the three faces of the y-rotor exhibit very

different hydrophobicities, that is, different

AGHA

values, namely, approximately -20,0, and

-i-9kcal/mole.

Furthermore, the most hydrophobic face

of the y-rotor functions as such; it associates

hydrophobically with the P-empty subunit,

which becomes the most hydrophobic p-

subunit due to the absence of polar (charged)

nucleotides.

The Fi-ATPase exhibits extensive "waters

of Thales"; as required for the existence of an

apolar-polar repulsive free energy of hydra-

tion, water-filled clefts exist between the y-rotor

and polar nucleotide filled sites.

Negative cooperativity for binding of ATP

occurs because each ATP addition is con-

fronted through the "waters of Thales" with a

progressively more hydrophobic face of the

rotor; the consequence of increases in the

apolar-polar repulsive free energy of hydra-

tion, AGap, constitute increasing barriers to the

approach of polar ATP molecules and result in

stepwise decreases in binding affinity.

The hydrophobic consihent mechanism

gives a functional role to the a-ATP noncat-

alytic sites; these sites provide a fixed triangu-

lation of repulsive AGap that helps to center the

rotor and to prevent locking up due to the vis-

coelastic drag of hydrophobic association.

6. As each of the p-catalytic sites fills with

ATP,

the rate of hydrolysis would increase due

to the decrease in viscoelastic drag that would

424

8. Consilient Mechanisms for Protein-based Machines of Biology

result in a progressively increased rotational

rate of the y-rotor, that is, there exists a positive

cooperativity in the catalytic rate as all P-

catalytic sites become occupied with ATP.

Because assembly of the Fi-ATPase is

dominated by an inverse temperature transi-

tion of hydrophobic association, the structure

disassembles on lowering the temperature, that

is,

it exhibits cold denaturation.

8. The maximal apolar-polar repulsive free

energy of hydration, AGap, acting through the

"waters of Thales," occurs between the most

hydrophobic side of the y-rotor and the most

polar state of the p-catalytic site, ADP^" Mg^"^

plus hydrolyzed phosphate, HPO4". The struc-

tural relationship between the sulfate analogue

of the hydrolyzed phosphate and the most

hydrophobic side of the y-rotor predicts the

direction of rotation for the Fi-ATPase to be

counterclockwise. Furthermore, this decisive

repulsive thrust indicates why the second chain

of the two-stranded a-helical coiled coil con-

tinues to the level of the y-phosphate of ATP

and is no longer and no shorter than it needs to

be for this function.

9. The remarkably high efficiency of the Fi-

ATPase in converting the chemical energy of

ATP hydrolysis into the performance of

mechanical work occurs because the repulsive

force acts through solvent to produce a

reversible elastic deformation of y-rotor and

the ((xP)3 housing, rather than a mechanical

mechanism where the steps of binding ATP and

its hydrolysis could be expected to cause con-

formational changes in the apical portions of

the p subunit that mechanically drove the

eccentric cam-like strucure of the y-rotor as

it enters the (aP)3 structure as an off-center

double-stranded helical coiled coil.

8,4,6,2 Restatement of the Critical

Synthesis Step of ATP Synthase

In the eighth point of correlation of the

hydrophobic elastic consilient mechanism given

above, the maximal stage of apolar-polar

repulsion occurred when the most polar occu-

pancy state, ADP^- Mg^^ plus

HPOf,

faced off

against the most hydrophobic side of the y-rotor

to provide the thrust for a counterclockwise

rotation. When the y-rotor is driven in a clock-

wise direction by the Fo-motor of ATP synthase,

the most hydrophobic face of the y-rotor is

driven into a face-off with the most polar occu-

pancy

state,

ADP^"

Mg^^

plus

HPOj",

to result in

a maximal apolar-polar repulsion that is

relieved by the formation of ATP. This we

beUeve is the mechanism whereby this pivotal

protein-based machine of living organisms

achieves its essential function of producing

nearly 90% of biology's energy for performing

the many functions required in the process of

sustaining Life.

8.5 The Myosin II Motor of

Muscle Contraction, a

Representative ATPase

8.5.1 Hypothesis: Efficient Production

of Motion by Muscle Contraction

Derives from the Hydrophobic and

Elastic Consilient Mechanisms,

Whereby Dephosphorylation Results

in Hydrophobic Association Coupled

to Near-ideal Elastic Force

Development

8.5.2 Coherence of Phenomena

Between Contraction of Muscle

and Contraction of Model Proteins

Using the Inverse Temperature

Transition

As reviewed in Chapter 7 with a focus on the

issue of insolubiUty, extensive phenomenologi-

cal correlations exist between muscle contrac-

tion and contraction by model proteins capable

of inverse temperature transitions of hydropho-

bic association. As we proceed to examination

of muscle contraction at the molecular level, a

brief restatement of those correlations follows

with observations of rigor at the gross ana-

tomical level and with related physiological

phenomena at the myofibril level. Each of the

phenomena, seen in the elastic-contractile

model proteins as an integral part of the com-

prehensive hydrophobic effect, reappear in the

properties and behavior of muscle. More com-

plete descriptions with references are given in

Chapter 7, sections 7.2.2, and 7.2.3.