Proteolytic enzymes of the formed elements of human blood. I. Erythrocytes.

A review of the literature conveys the impression that proteolytic enzymes capable of splitting protein substrates are largely associated with the plasma of mammalian blood, whereas enzymes acting on simple peptides are preponderantly associated with the formed elements. Thus, upon removal of inhibitory fractions from blood plasma, proteinases akin to trypsin and related to the process of blood coagulation have been recognized by several investigators (1, 2). Conversely, leucocytes and erythrocytes have been shown to have a high activity toward di-, tri-, and tetrapeptides of glycine, alanine, and leucine ((3) for a review of the literature see Stern et al. (4)). The question of the occurrence of protein-splitting enzymes in suspensions or extracts of platelets, erythrocytes, or leucocytes is an important one in consideration of the stability and metabolism of these cells. As part of a program designed to characterize the enzymatic components of the formed elements of human blood, the proteinase activity of erythrocytes has, therefore, been investigated. The results of this work are presented in this communication, whereas, in a paper to follow, the proteinase activity of human leucocytes will be described.