Changes associated with glycolytic-enzyme binding in the equatorial X-ray-diffraction pattern of glycerinated rabbit psoas muscle.

The binding of fructose biphosphate aldolase to the thin filaments of glycerinated rabbit psoas muscle produces a significant change in its low-angle X-ray-diffraction pattern. The intensity of the (11) reflection relative to that of the (10) reflection increases by 26 +/- 3% (mean +/- S.E.M.), which is consistent with the increase in the mass of the thin filaments produced by enzyme binding. A similar effect is found with a mixture of aldolase and glyceraldehyde 3-phosphate dehydrogenase. The significance of the change in intensity is considered with reference to the interpretation of the equatorial patterns obtained from muscles in different physiological states. The magnitude of the increase in the relative intensity of the (11) reflection is lower than that observed between relaxed and contracting muscle and does not bring into question the interpretation linking changes in these patterns to cross-bridge movement. However, the effect due to enzyme binding may be important when making detailed interpretations of these changes. It may also be related to an unusual pattern sometimes observed in cardiac muscle.