Characterization of lactate dehydrogenase enzyme in seminal plasma of Japanese quail (Coturnix coturnix japonica)

Lactate dehydrogenase enzyme present in quail seminal plasma has been characterized. Polyacrylamide gel electrophoresis and subsequently with LDH specific staining of seminal plasma revealed a single isozyme in quail semen. Studies on substrate inhibition, pH for optimum activity and inhibitor (urea) indicated the isozyme present in the quail semen has catalytic properties like LDH-1 viz. H-type. Furthermore, unlike other mammalian species, electrophoretic and kinetic investigations did not support the existence of semen specific LDH-X isozyme in quail semen. The effect of exogenous lactate and pyruvate on sperm metabolic activity was also studied. The addition of 1 mM lactate or pyruvate to quail semen increased sperm metabolic activity. Our results suggested that both pyruvate and lactate could be used by quail spermatozoa to maintain their basic functions. Since the H-type isozyme is important for conversion of lactate to pyruvate under anaerobic conditions it was postulated that exogenous lactate being converted into pyruvate via LDH present in semen may be used by sperm mitochondria to generate ATP. During conversion of lactate to pyruvate NADH is being generated that may be useful for maintaining sperm mitochondrial membrane potential.