Factors affecting the release of proteases from peripheral blood monocytes.

Serum amyloid A (SAA) protein is degraded by serine proteases associated with the external plasma membrane of peripheral blood monocytes. The plasma membrane-associated enzymes are serine proteases of high molecular weight. In addition, cells grown in suspension release enzymatic activity into the surrounding medium. The origin and nature of the released SAA degrading enzymes remains obscure, but they appear to belong to the general class of serine proteases. Conditions of culture were determined which minimized release of the secreted enzymes and will ultimately permit the characterization of the properties of the membrane associated enzymes uncontaminated with the cytoplasmic proteases. It seems likely that there are two compartments of proteases-one surface-associated and one cytoplasmic.