title: Purification, physicochemical, and kinetic properties of liver acetyl-CoA:arylamine N-acetyltransferase from rapid acetylator rabbits.
abstract: Cytosolic liver acetyl-CoA:arylamine N-acetyltransferase (EC 2.3.1.5) from homozygous rapid acetylator rabbits (strain III/J) was purified to homogeneity as judged by gel filtration sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis and isoelectrofocusing. The isoelectric point was estimated to be 5.2. The molecular weight was determined to be 33,500 by sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis and 33,000 by Sephacryl S-200 gel filtration. The amino acid composition is reported and 16 tryptic peptides were sequenced by Edmann degradation, including a peptide from which a very specific oligonucleotide probe can be synthesized. The enzyme contained neither amino sugars nor cofactors. A broad pH optimum from pH 5.9 to 8.6 was observed. N-Acetyltransferase activity showed a strong dependency on the salt concentration. From the influence of the basicity of the acceptor amine on the maximum velocity, it was concluded that the formation of the covalent acetyl-enzyme intermediate is the rate-limiting step in the N-acetyltransferase-catalyzed acetylation of amines. The covalent intermediate reacts, then, in a fast step with the acceptor amine, when using aniline derivatives with pKa values ranging from 5.65 to 1.74. However, with the weakly basic 4-nitroaniline, the acetyltransfer from the catalytic intermediate to the amine seems to be rate-limiting. A structure-activity study of 30 aniline derivatives that differ in hydrophobicity, position, size, charge, and number of substituents showed that some ortho-substituted derivatives were not acetylated.
mesh_terms: D000107:Acetylation; D000123:Acetyltransferases / Q000302:isolation & purification*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000302:isolation & purification*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D011817:Rabbits; D013329:Structure-Activity Relationship; D014357:Trypsin / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000123:Acetyltransferases; D001191:Arylamine N-Acetyltransferase; D014357:Trypsin