PLASMA-MEMBRANE PROTEASES OF LYMPHOID-CEL LS AND THEIR BIOLOGICAL FUNCTIONS

The properties, distribution, and biological functions of several prot eases from-the plasma membrane of lymphoid cells are reviewed: dipepti dyl peptidase IV, neutral endopeptidase, aminopeptidases A and N, and a new protease of the family of adamalysins. These enzymes (designated as ectopeptidases) are integral membrane proteins whose molecules are mainly located extracellularly. Their functions involve proteolysis o n the cell surface: the formation and inactivation of regulatory pepti des and growth factors, as well as modification of cell surface protei ns. The biological significance of a partial proteolysis of the plasma membrane proteins and the resulting soluble isoforms are discussed. A n analysis of the data suggests that ectopeptidases from lymphoid cell s are elements of the sensory system of the cell and are involved in t he regulation of its physiological response to external factors and in the coordination of cell-cell interactions.