The isoforms of human neutrophil elastase and cathepsin G differ in their carbohydrate side chain structures.

The two proteinases found in human neutrophil granules, elastase and cathepsin G, each are normally isolated as a mixture of isoforms differing only in carbohydrate content. Elastase has two N-glycosylation sites occupied (Asn-45 and Asn-144), whereas cathepsin G has only one (Asn-64). Analysis of a minor form of elastase (E-1) and cathepsin G (C-1) indicates that the carbohydrate structures at each glycosylation site are complex-type bi-antennary chains usually associated with secretory glycoproteins. In contrast, the isoforms E-3 and C-3, the major forms of elastase and cathepsin G respectively, contain exclusively truncated, oligomannose-type chains at the same positions in the sequence of each protein. These data suggest the possibility that certain elastase and cathepsin G isoforms (E-1 and C-1) might be destined for secretory, others (E-3 and C-3) for lysosomal functions.