Abstract
Abstract 1. Kinetic data have been obtained with the purified X4 isozyme of lactic dehydrogenase (EC 1.1.1.27) from rabbit and human spermatozoa, and compared with the data for the purified H4 and M4 isozymes. The studies indicate that the rabbit or human X4 isozymes have enzymatic properties very similar to those of the rabbit or human H4 isozymes, respectively. 2. The average molecular weight of the rabbit X4 isozyme was estimated by sucrose density gradient to be 150,000, identical with that of the rabbit H4 isozyme, while the rabbit M4 isozyme had an average molecular weight of 140,000. 3. The distribution of the X4 isozyme in various rabbit tissues was investigated, and bands corresponding to the X4 isozyme were found in the seminal fluid, and in extracts of heart, kidney, and the ampulla, as well as in the testes and spermatozoa. 4. Kinetic data concerning substrate inhibition by l-lactate of the rabbit H4 isozyme subbands was obtained, which demonstrate that these subbands do not all have the same enzymatic properties. 5. The electrophoretic patterns, molecular weights, heat stabilities, and enzymatic properties were interpreted as suggesting that the X4 isozyme and the subbands of rabbit lactic dehydrogenase are tetramers formed by hybrid subunits, and are not controlled by genes other than those controlling the synthesis of the H4 and M4 isozymes.
Highlights
Kinetic data concerning substrate inhibition by L-lactate of the rabbit H4 isozyme subbands was obtained, which demonstrate that these subbands do not all have the same enzymatic properties
The results indicate that the rabbit X4 isozyme has enzymatic properties similar to those of the rabbit Hq isozyme, and the human Xq isozyme has properties similar to those of the human Hq isozyme
Wilkinson and Withycombe [14] reported that the isolated human X4 isozyme resembles the human Hh isozyme in that it is strongly inhibited by 0.2 mM oxalate and relatively resistant to 2.0 M urea, and is relatively stable to heat
Summary
Materials-Crystalline rabbit muscle lactic dehydrogenase catalase and beef liver catalase were obtained from Worthington. A 40% solution of L(+)-lactic acid was obtained from Sigma and the concentration was checked by titration. T. Baker Chemical Company and redistilled before use. Diphosphopyridine nucleotide (DPNf), A grade, and DPNH were obtained from Calbiochem. M-oc-hydroxy-n-valeric acid, and imidazole pyruvic acid were obtained from Sigma. T. Baker Chemical Company were Tris, EDTA, and sodium pyrosphosphate, all reagent grade.
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