Acylase I-Catalyzed Deacetylation of N-Acetyl-l-cysteine and S-Alkyl-N-acetyl-l-cysteines

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Abstract
The aminoacylase that catalyzes the hydrolysis of N-acetyl-l-cysteine (NAC) was identified as acylase I after purification by column chromatography and electrophoretic analysis. Rat kidney cytosol was fractionated by ammonium sulfate precipitation, and the proteins were separated by ion-exchange column chromatography, gel-filtration column chromatography, and hydrophobic interaction column chromatography. Acylase activity with NAC and N-acetyl-l-methionine (NAM), a known substrate for acylase I, as substrates coeluted during all chromatographic steps. Sodium dodecyl sulfate−polyacrylamide gel electrophoresis showed that the protein was purified to near homogeneity and had a subunit Mr of 43 000, which is identical with the Mr of acylase I from porcine kidney and bovine liver. n-Butylmalonic acid was a slow-binding inhibitor of acylase I and inhibited the deacetylation of NAC with a Ki of 192 ± 27 μM. These results show that acylase I catalyzes the deacetylation of NAC. The acylase I-catalyzed deacetylation of a range of S-alkyl-N-acetyl-l-cysteines, their carbon and oxygen analogues, and the selenium analogue of NAM was also studied with porcine kidney acylase I. The specific activity of the acylase I-catalyzed deacetylation of these substrates was related to their calculated molar volumes and log P values. The S-alkyl-N-acetyl-l-cysteines with short (C0−C3) and unbranched S-alkyl substituents were good acylase I substrates, whereas the S-alkyl-N-acetyl-l-cysteines with long (>C3) and branched S-alkyl substituents were poor acylase I substrates. The carbon and oxygen analogues of S-methyl-N-acetyl-l-cysteine and the carbon analogue of S-ethyl-N-acetyl-l-cysteine were poor acylase I substrates, whereas the selenium analogue of NAM was a good acylase I substrate.