STEADY STATE RELAXATION OF ENOLASE IN VITRO AND METABOLIC THROUGHPUT IN VIVO OF RED AND WHITE RABBIT MUSCLES

The kinetics of rabbit muscle enolase in vitro are shown to follow a first order time law at substrate concentrations above as well as within the range of the Michaelis constants. The product (τssV1), where τss is the steady state relaxation time and V1 the maximum velocity in the forward direction, is found to be essentially a function of the total reactant concentration, and is almost independent of pH: (Formula Presented.) , being the millimolar concentration of phosphoenolpyruvate at equilibrium. An expression for the relative steady metabolic throughput in vivo at the enolase step is derived. The deviation from apparent equilibrium and total reactant level are the important variables. For convenient use, a nomogram is given (see Fig.5). The thus developed expressions are then applied to red and white rabbit muscle at different states of activity. A calculation of the absolute metabolic throughput with available metabolite and enzyme level data correlates with the measured rate of lactate production. “Glycolytic potencies”, as deduced recently from enzyme patterns of the two muscles, prove to be proportional to the measured metabolic throughputs. The high cellular activity of enolase and other glycolytic enzymes is interpreted to serve mainly to minimize the deviation and the concomitant expenditure of free energy. The energy expended for the enolase step at maximal glycolytic flux is calculated to be 0.6 kcal per mole of lactate formed, in both types of muscle. Copyright © 1969, Wiley Blackwell. All rights reserved