A Comparison of Some Kinetic Properties of Soluble and Bound Lactate Dehydrogenase Isoenzymes at Different Temperatures

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Abstract
A comparison was made of some kinetic properties of 3 chicken lactate dehydrogenase [LDH, EC 1.1.1.27] isoenzymes (1, 3 and 5) at 4, 16, 23 and 40.degree. C. Assays were performed with an enzyme concentration of 0.01 .mu.M at pH 6.0. Under the conditions of assay, LDH 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 and 5 to the cellular particulate fraction decreased V. This decrease was much greater for LDH 5 than 3. Values of V for LDH isoenzymes 1 and 3 did not follow a simple Arrhenius relationship; there was a rapid change in activity between 16 and 23.degree. C. The apparent Km (pyruvate) values of all isoenzymes (bound or soluble) increased with increasing temperature, changing 4 to 10-fold. The apparent Km for LDH 5 was greater than that for LDH 3, which in turn was greater than that for LDH 1.