RESUMO
Adenosyl homocysteinase was prepared and purified till homogenecidy gel chromatography. The molecular weight and amino acid composition of the native enzyme were determined before and after modification of cysteinyl residue by iodoacetamide. Also the native enzyme was labelled covalently by fluorescent isothiocyanate causing inhibition of its activity. The fluorescent labelled enzyme was digested by trypsin and the fluorescent labelled peptide was isolated and the amino acid composition of this peptide was identified. The experimental data indicate that fluorescent isothiocyanate can react with lysinyl residue; which is associated with cysteine in the catalytic function of the enzyme. The catalytic activity of adenosyl homocysteinase was inhibited after incubation of the enzyme with either iodoacetate or 2-deoxycoform either iodoacetate or 2-deoxycoformycin. 2-Deoxycoformycin interact with the enzyme bound NAD causing local conformational change by which the enzymatic activity was inhibited