CHARACTERIZATION OF THE ACYL-COA-AMINO ACID N-ACYLTRANSFERASES FROM PRIMATE LIVER-MITOCHONDRIA

The acyl-CoA:amino acid N-acyltransferases were partially purified fro m human liver mitochondria. The aralkyl transferase (ArAlk) had glycin e conjugating activity toward the following compounds: benzoyl-CoA > b utyryl-CoA, salicylyl-CoA > heptanoyl-CoA, indoleacetyl-CoA. Its kinet ic properties and responses to salt were very similar to those of bovi ne ArAlk. Further, its molecular weight was found to be similar to tha t of the bovine enzyme, in contrast to reports from other laboratories . Thus, it was concluded that the human and bovine ArAlk are not signi ficantly different. The human arylacetyl transferase (AAc) had glutami ne conjugating activity toward phenylacetyl-CoA, but only 3-5% as much activity toward indoleacetyl-CoA or 1-naphtylacetyl-CoA, respectively . While this was similar to the bovine AAc, the two forms differed in several respects. First, the human liver AAc was insensitive to salts. Second, glycination of phenylacetyl-CoA by human AAc could only be de tected at a high concentration of glycine (50 mM), and the rates were <2% of the rate of glutamination. In contrast, glycine conjugation pre dominates with bovine AAc. Kinetic analysis of the glutamination of ph enylacetyl-CoA by human AAc revealed a K(D) for phenylacetyl-CoA of 14 muM and a K(m) for glutamine of 120 mM. These values indicate that th e human AAc is not more efficient at glutamination than the AAc from b ovine liver. An AAc was purified from rhesus monkey liver and found to have similar kinetic constants to the human form. This indicates that nonprimate enzymes do not have a defect in glutamine conjugation. Rat her, it is the primate forms that are defective in that they have lost glycine conjugation, not increased the efficiency of glutamine conjug ation.