TRANSAMIDATION REACTIONS CATALYZED BY CATHEPSINS

Abstract

Cathepsin B is an intracellular proteinase found in several animal tissues (1, 2), and has been partially purified from beef spleen (3).Its specificity appears to be directed toward the hydrolysis of amide (or ester) bonds involving cu-N-acylated n-arginine or L-lysine (3).Thus, at pH 5, cathepsin B catalyzes the hydrolytic cleavage of benzoyl-L-argininamide (BAA) to benzoyl-n-arginine and NH,+.Only fragmentary data were available (4) on the ability of cathepsin B to catalyze transamidation reactions; studies on this question are reported in the present communication.Another intracellular proteinase of animal tissues, denoted cathepsin C, also has been partially purified from beef spleen (5, 6) ; at pH 5 to 7, this enzyme catalyzes the hydrolysis of dipeptide amides (or esters) of suitable structure (7-9).Cathepsin C is an excellent catalyst of transamidation reactions (10) ; for example, at pH 7.5, glycyl-L-tyrosinamide (GTA) is polymerized to a decapeptide composed of alternating glycyl and n-tyrosyl residues (11).Since these two proteinases occur in the same tissues, and may be located in the same subcellular elements (2, 12), it was of interest to examine their coupled action in effecting the specific elongation of a peptide chain.Experiments reported in the present communication suggest that a mixture of cathepsins B and C catalyzes a sequence of reactions leading to the synthesis of n-prolyl-L-tyrosyl-L-arginylglycyl-n-leucine from Lprolyl-L-tyrosinamide, L-argininamide, and glycyl-n-leucine.