Organization of enzymes in the synthesis of peptides

Abstract

We have undertaken the investigation of the nature of the intracellular peptidases and transpeptidases in the belief that the information will be pertinent to an understanding of the genetic behaviour and growth of an organism or, simply, the synthesis of protein. It cannot be argued that the peptidases and transpeptidases are responsible for all steps in protein synthesis; the participation of peptidases in the synthesis of peptides and proteins would require that energy be derived from coupled reactions. Nevertheless, it would seem obvious that the peptidases are concerned with the synthesis of protein; peptidase activity is greatest in rapidly growing tissue and may be correlated with the mitotic rate of various types of cells. In addition, it is easily demonstrated that the peptidases can, in the presence of a suitable linked source of energy, catalyze the formation of dipeptides. Energy mechanisms are required, but these energy mechanisms are probably coupled with exchange reactions of many different types and specificities; these specificities may well be furnished by the peptidases. Our studies have indicated that the peptidase activities of a cell are a property of the polynucleotides of the cell (Binkley 1952). In our studies of the hydrolysis of glutathione (Olson & Binkley 1950) it became necessary to study the hydrolysis of the cysteinylglycine. Our most highly purified preparations of the enzyme have been found to be non-specific in nature and to hydrolyze all dipeptides not having an amino-acid of the D-configuration as the initial amino-acid. Leucylglycine, a substrate for the so-called leucine aminopeptidase activity of cells, is easily prepared and is an excellent substrate for studies of the non-specific dipeptidase; this substrate has been used in all our more recent work.