  Initial reaction rate data for lactic dehydrogenase / pyruvate, lactic
dehydrogenase / lactate and malic dehydrogenase / malate enzyme reactions were
analyzed to obtain activation free energy changes of -329, -195 and -221
cal/mole, respectively, for rate increases associated with time-specific
irradiation of the crystalline substrates prior to dissolution and
incorporation in the reaction solutions. These energies, presumably, correspond
to conformational or vibrational changes in the reactants or the activated
complex. For the lactic dehydrogenase / pyruvate reaction, it is estimated that
on the order of 10% of the irradiation energy (546 nm, 400 footcandles for 5
seconds) would be required to produce the observed reaction rate increase if a
presumed photoproduct is consumed stoichiometrically with the pyruvate
substrate. These findings are consistent with the proposition that the observed
reaction rate enhancement involves photoproducts derived from oscillatory
atmospheric gas reactions at the crystalline enzyme substrate surfaces rather
than photo-excitations of the substrate molecules, per se.

Subcellular Processes;Biomolecules