Non enzymatic glycosylation of alpha-1-proteinase inhibitor of human plasma.

ABSTRACT

Human plasma contains inhibitors, which control the activity of proteolytic enzymes. Alpha-1-proteinase inhibitor and alpha-2-macroglobulin are two of them present in high concentration in human plasma, which inhibit action of trypsin among other proteinases. The trypsin inhibitory capacity (TIC) of human plasma is observed to be decreased in pathological conditions like diabetes mellitus. The mechanisms of decrease in TIC was due to nonenzymatic glycosylation of alpha-1-proteinase inhibitor (A1PI). A1PI was partially purified from normal human plasma by steps involving ammonium sulphate precipitation, DEAE Sepharose CL6B chromatography, Concanavalin A Sepharose Chromatography and Sephadex G-100 Gel filtration. Purified inhibitor was glycosylated in vitro by incubating it with varying glucose concentrations, under nitrogen for different periods of time in reducing conditions. After glycosylation, the molecular weight of inhibitor increased from 52 kDa to 57 KDa because of binding with glucose molecules. The percent free amino groups in the protein decreased with increasing glucose concentration and days of incubation. The TIC of such modified inhibitor decreased significantly. Decrease in TIC was dependent on the glucose concentration and period of incubation used during in-vitro glycosylation of native inhibitor.