Transamination of neutral amino acids and 2-keto acids in pancreatic B-cell mitochondria.
High aminotransferase activities catalyzing the reactions between L-glutamate and L-glutamine and the aliphatic ketomonocarboxylic acids 2-ketoisocaproate, 2-ketocaproate, and 2-ketoisovalerate were observed in pancreatic B-cell mitochondria. While maximal rates of transamination with L-glutamate were observed in the presence of micromolar concentrations of keto acid, maximal rates of transamination with L-glutamine were recorded only in the presence of millimolar concentrations of keto acid. The insulin secretagogue 2-ketoisocaproate was the most effective transamination partner for L-glutamate, while the insulin secretagogue 2-ketocaproate was the most effective transamination partner for L-glutamine. Since B-cell mitochondria are well supplied with L-glutamate and L-glutamine, 2-ketoglutarate generation in the presence of these two neutral 2-keto acids may be an important prerequisite for their insulin secretory potency. High rates of transamination of 2-ketoglutarate were observed in the pancreatic B-cell mitochondria with the branched-chain amino acids L-leucine and L-valine, but not with L-norleucine. In connection with the ability of L-leucine to activate glutamate dehydrogenase, this high activity of the branched-chain amino acid aminotransferase in pancreatic B-cell mitochondria may provide an explanation for the insulin secretory potency of this amino acid.
Lenzen
S
S
Schmidt
W
W
Panten
U
U
D000818:Animals; D002208:Caproates / Q000378:metabolism; D003593:Cytoplasm / Q000201:enzymology; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D005973:Glutamine / Q000378:metabolism*; D045782:Hemiterpenes; D007515:Islets of Langerhans / Q000201:enzymology*; D007651:Keto Acids / Q000378:metabolism*; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D051379:Mice; D008820:Mice, Obese; D008928:Mitochondria / Q000201:enzymology; D000637:Transaminases / Q000378:metabolism*; D014633:Valine / Q000378:metabolism
D002208:Caproates; D005971:Glutamates; D045782:Hemiterpenes; D007651:Keto Acids; D005973:Glutamine; C001916:alpha-ketocaproic acid; D018698:Glutamic Acid; C001505:alpha-ketoisovalerate; C013082:alpha-ketoisocaproic acid; D000637:Transaminases; D007930:Leucine; D014633:Valine