Partial Chemical Characterization of alpha- and beta-Momorcharins

Abstract

The chemical characteristics of α-momorcharin (α-M), β-momorcharin (β-M), and trichosanthin (T), proteins with abortifacient, immunosuppressive, and antitumor activities, are compared. The molecular masses of α-M, β-M, and T are respectively 29 000, 28 000 and 26 000. The former two are glycoproteins with a neutral sugar content of, respectively, 1.6% and 1.3%, while the latter is a non-glycoprotein. All three proteins carry Asp at the NH₂-terminus, and they are rich in Asp/Asn and Glu/Gln residues, but do not possess Cys residues. α-M and T have a low methionine content while β-M is totally lacking in methionine residues. Partial sequencing of α-M and T at the NH₂-terminus reveals seven identical residues out of the twelve examined in the two proteins.

Cyanogen bromide digestion of α-M and T yields several fragments but β-M does not yield any fragments upon digestion. Digestion of the proteins with proteases produces different patterns of peptide fragments as revealed by SDS-polyacrylamide gel electrophoresis. The immunoprecipitin arcs formed in immunodiffusion between the proteins and their antisera intersect one another.