title: Use of aromatic amino acids as monitors of protein turnover.
abstract: Phenylalanine and tyrosine were metabolized by the perfused rat heart via a mitochondrial aminotransferase. When L-[alanyl-2,3-3H]phenylalanine and L-[alanyl-2,3-3H]tyrosine were used, release of 3H2O was progressive over 2 h of perfusion. Metabolism of L-[U-14C]phenylalanine to 14CO2 or production of 3H2O from L-[ring-2,6-3H]phenylalanine or L-[ring-2,6-3H]tyrosine was not detected. Although 3H2O production from L-[alanyl-2,3-3H]phenylalanine was rapid, net production of phenylpyruvate or other metabolites of phenylalanine was negligible. As a result, use of aromatic amino acids as monitors of protein turnover in heart muscle was validated. Production of 3H2O from L-[alanyl-2,3-3H]phenylalanine was catalyzed by a mitochondrial enzyme, which is thought to be aspartate aminotransferase (EC 2.6.1.1). The rate of 3H2O production by both intact and detergent-treated mitochondria exceeded that of phenylpyruvate by a factor of 10 and occurred in the absence of alpha-ketoglutarate. These data provide an explanation for the production of 3H2O from L-[alanyl-2,3-3H]phenylalanine by perfused rat heart without the concomitant production of [3H]phenylpyruvate.
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D000818:Animals; D002250:Carbon Radioisotopes; D005947:Glucose / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism*; D010649:Phenylalanine / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D000637:Transaminases / Q000378:metabolism*; D014316:Tritium; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D002250:Carbon Radioisotopes; D011506:Proteins; D014316:Tritium; D014443:Tyrosine; D010649:Phenylalanine; D000637:Transaminases; D005947:Glucose