Branched-chain amino acid aminotransferase in mouse testicular tissue.
Branched-chain amino acid aminotransferase (L-leucine:2-oxoglutarate aminotransferase, EC 2.6.1.6) activity was determined in several tissues of the mouse. Testis homogenates presented a specific activity very close to that of heart extracts which were the most active. Enzyme activity was detectable in testes from 5-day-old mice and increased steadily during development to reach a maximum at the 20th day of life. The transaminase was present in the cytosol of testicular homogenates and also associated, probably in the matrix, with a special type of mitochondria present in spermatozoa and gametogenic cells. The enzyme from testis is active against the three branched-chain amino acids and catalyses the reaction in both directions. Highest activity and lowest Km were obtained with L-leucine. Activity with L-valine was the lowest. The enzyme from the mitochondrial fraction showed identical properties to that from the soluble phase. The possible participation of this aminotransferase in a shuttle system transferring reducing equivalents from cytoplasm to mitochondria is postulated.
D000818:Animals; D007656:Ketoglutaric Acids; D007700:Kinetics; D007930:Leucine; D008297:Male; D051379:Mice; D008928:Mitochondria / Q000201:enzymology; D013347:Subcellular Fractions / Q000201:enzymology; D013737:Testis / Q000201:enzymology*; D000637:Transaminases / Q000378:metabolism*
D007656:Ketoglutaric Acids; D000637:Transaminases; D007930:Leucine