Novelty of the pyruvate metabolic enzyme dihydrolipoamide dehydrogenase in spermatozoa - Correlation of its localization, tyrosine phosphorylation, and activity during sperm capacitation

Spermatozoa are cells distinctly different from other somatic cells of the body, capacitation being one of the unique phenomena manifested by this gamete. We have shown earlier that dihydrolipoamide dehydrogenase, a post- pyruvate metabolic enzyme, undergoes capacitation dependent tyrosine phosphorylation, and the functioning of the enzyme is required for hyperactivation ( enhanced motility) and acrosome reaction of hamster spermatozoa ( Mitra, K., and Shivaji, S. ( 2004) Biol. Reprod. 70, 887 - 899). In this report we have investigated the localization of this mitochondrial enzyme in spermatozoa revealing non- canonical extra- mitochondrial localization of the enzyme in mammalian spermatozoa. In hamster spermatozoa, dihydrolipoamide dehydrogenase along with its host complex, the pyruvate dehydrogenase complex, are localized in the acrosome and in the principal piece of the sperm flagella. The localization of dihydrolipoamide dehydrogenase, however, appears to be in the mitochondria in the spermatocytes, but in spermatids it appears to show a juxtanuclear localization ( like Golgi). The capacitation- dependent time course of tyrosine phosphorylation of dihydrolipoamide dehydrogenase appears to be different in the principal piece of the flagella and the acrosome in hamster spermatozoa. Activity assays of this bi- directional enzyme suggest a strong correlation between the tyrosine phosphorylation and the bi- directional enzyme activity. This is the first report of a direct correlation of the localization, tyrosine phosphorylation, and activity of the important metabolic enzyme, dihydrolipoamide dehydrogenase, implicating dual involvement and regulation of the enzyme during sperm capacitation.