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An Aminoacyltransferase Preparation from Beef Liver

From the ¹ From the Department of Biochemistry, Yale University, New Haven, Connecticut 06520

An aminoacyltransferase preparation has been obtained from a beef liver homogenate, and a 44-fold purification of the activity has been achieved. The enzyme preparation catalyzes both peptide synthesis from suitable amino acid esters (e.g. phenylalanine methyl ester, tyrosine methyl ester, leucine methyl ester) and the hydrolysis of such esters, the former process predominating at pH values near 7. Both actions are completely inhibited by diisopropyl phosphorofluoridate. Evidence is presented to show that in the formation of dipeptides (e.g. phenylalanylphenylalanine) from amino acid esters (e.g. phenylalanine methyl ester), the corresponding dipeptide ester is an intermediate. In peptide synthesis, the enzyme preparation exhibits side chain specificity with respect to both the acyl donor and the amine acceptor, but the specificity with respect to the amine acceptor appears to be more restricted, and limited to esters of certain L-amino acids. Amino acid amides and peptide amides corresponding to susceptible esters are resistant to enzymic action.

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