A comparison of some kinetic properties of soluble and bound lactate dehydrogenase isoenzymes at different temperatures.

A comparison was made of some kinetic properties of three chicken lactate dehydrogenase isoenzymes (1, 3 and 5) at 4, 16, 23 and 40 degrees C. Assays were performed with an enzyme concentration of 0.01 muM at pH 6.0. Under the conditions of assay, lactate dehydrogenase 3 and 5 bound to the particulate fraction of homogenized skeletal muscle and were evaluated in the soluble and particulate state. Binding of isoenzymes 3 and5 to the cellular particulate fraction decreased V. This decrease was much greater for lactate dehydrogenase 5 and 3. Values of V for lactate dehydrogenase isoenzymes 1 and 3 did not follow a simple Arrhenius relationship; there was a rapid change in activity between 16 and 23 degrees C. The apparent Km (pyruvate) values of all isoenzymes (bound or soluble) increased with increasing temperature, changing 4--10-fold. The apparent Km for lactate dehydrogenase 5 was greater than that for lactate dehydrogenase 3, which in turn was greater than that for lactate dehydrogenase 1.