Processing of rat and human angiotensinogen precursors by microsomal membranes

We have studied the processing of rat and human angiotensinogen precursors by microsomal membranes as a means of determining the number of asparagine-linked oligosaccharide units per angiotensinogen molecule, and thus the utilization of potential sites of N-glycosylation. Glycosylated, processed forms of angiotensinogen were isolated by chromatography on lentil lectin-Sepharose 4B. 35S-Methionine-labeled precursor and processed forms of angiotensinogen were compared with glycosylated and nonglycosylated 35S-methionine-labeled mature forms of angiotensinogen secreted by hepatoma cells, using immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. N-Glycosylation of secreted angiotensinogen was inhibited using tunicamycin. For rat angiotensinogen, only 2 of 3 potential sites of N-glycosylation were utilized; in contrast, all 4 potential sites of N-glycosylation of human angiotensinogen were utilized. For neither rat or human angiotensinogen precursor was there any evidence for a prosequence.