Determination of the sequence of the aralkyl acyl-CoA:amino acid N-acyltransferase from bovine liver mitochondria

The aralkyl acyl-CoA:amino-acid N-acyl-transferase was previously purified to homogeneity from bovine liver mitochondria. The N-terminal amino-acid sequence and sequences obtained by cyanogen bromide cleavage of the enzyme were used to design oligonucleotide probes that were used to screen a bovine liver cDNA library. Several clones were isolated and sequenced, and the sequence is given. The cDNA contains 126 bases of 5′-untranslated region and 188 bp of 3′ untranslated region. The cDNA codes for an enzyme containing 295 amino-acid residues. The sequence gives a molecular weight for the enzyme of 39,229, which is larger than previously estimated. The amino-acid composition of the enzyme, based on this sequence, is in agreement with the previously obtained amino-acid analysis on the purified kidney enzyme. © 1997 John Wiley & Sons, Inc.     

Characterization of the acyl-CoA: Amino acid N-acyltransferases from primate liver mitochondria

The acyl-CoA:amino acid N-acyl-transferases were partially purified from human liver mitochondria. The aralkyl transferase (ArAlk) had glycine conjugating activity toward the following compounds: benzoyl-CoA > butyryl-CoA, salicylyl-CoA > heptanoyl-CoA, indoleacetyl-CoA. Its kinetic properties and responses to salt were very similar to those of bovine ArAlk. Further, its molecular weight was found to be similar to that of the bovine enzyme, in contrast to reports from other laboratories. Thus, it was concluded that the human and bovine ArAlk are not significantly different. The human arylacetyl transferase (AAc) had glutamine 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 detected at a high concentration of glycine (50 mM), and the rates were <2% of the rate of glutamination. In contrast, glycine conjugation predominates with bovine AAc. Kinetic analysis of the glutamination of phenylacetyl-CoA by human AAc revealed a K_D for phenylacetyl-CoA of 14 μM and a K_m for glutamine of 120 mM. These values indicate that the human AAc is not more efficient at glutamination than the AAc from bovine 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. Rather, it is the primate forms that are defective in that they have lost glycine conjugation, not increased the efficiency of glutamine conjugation.