Epitopes of human testis-specific lactate dehydrogenase deduced from a cDNA sequence

The sequence and structure of human testis-specific L-lactate dehydrogenase [LDHC₄, LDHX; (L)-lactate:NAD⁺ oxidoreductase, EC 1.1.1.27] has been derived from analysis of a complementary DNA (cDNA) clone comprising the complete protein coding region of the enzyme. From the deduced amino acid sequence, human LDHC₄ is as different from rodent LDHC₄ (73% homology) as it is from human LDHA₄ (76% homology) and porcine LDHB₄ (68% homology). Subunit homologies are consistent with the conclusion that the LDHC gene arose by at least two independent duplication events. Furthermore, the lower degree of homology between mouse and human LDHC₄ and the appearance of this isozyme late in evolution suggests a higher rate of mutation in the mammalian LDHC genes than in the LDHA and -B genes. Comparison of exposed amino acid residues of discrete antigenic determinants of mouse and human LDHC₄ reveals significant differences. Knowledge of the human LDHC₄ sequence will help design human-specific peptides useful in the development of a contraceptive vaccine.