1987 Volume 35 Issue 3 Pages 1151-1156
Interactions in vitro and in vivo between semi-alkaline proteinase (SAP) and protease inhibitors of rabbit serum were studied. As a result of the purification of SAP inhibitors from rabbit serum, the caseinolytic activity of SAP was found to be inhibited by α1-macroglobulin (α1 M) and α1proteinase inhibitor (α1, PI). SAP was stoichiometrically bound to α1M at a molar ratio of 1 : 1 and the proteolytic activity remained constant at 16% of the original activity even in the presence of excess α1 M. In contrast, the proteolytic activity of SAP decreased linearly with increase in the amount of α1 PI, but a 10-fold molar excess of α1PI was needed for complete inhibition.
The disappearance rate of intravenously injected 125I-labeled SAP (125I-SAP) from rabbit serum was also investigated by using high-performance liquid chromatography (HPLC). Serum levels of 125I-SAP decreased biexponentially after a single injection. The results of gel-permeation HPLC of rabbit serum on a TSK G-3000 SW column indicated that SAP was mainly bound to α-macroglobulins and that α-macroglobulin-SAP complex was cleared from the blood circulation with a half-life of 10 min.
