THE CDNA CLONING AND MOLECULAR EVOLUTION OF REPTILE AND PIGEON LACTATE-DEHYDROGENASE ISOZYMES

The cDNAs encoding lactate dehydrogenase isozymes LDH-A (muscle) and L DH-B (heart) from alligator and turtle and LDH-A, LDH-B, and LDH-C (te stis) from pigeon were cloned and sequenced. The evolutionary relation ships among vertebrate LDH isozymes were analyzed. Contrary to the tra ditional belief that the turtle lineage branched off before the diverg ence between the lizard/alligator and bird lineages, the turtle lineag e was found to be clustered with either the alligator lineage or the a lligator-bird clade, while the lizard lineage was found to have branch ed off before the divergence between the alligator/turtle and bird lin eages. The pigeon testicular LDH-C isozyme was evidently duplicated fr om LDH-B (heart), so it is not orthologous to the mammalian testicular LDH-C isozymes.