Peptide Mapping Reveals Considerable Sequence Homology among the Three Polypeptide Subunits of G1 Storage Protein from French Bean Seed

Abstract

The major storage protein, G1 globulin, of bean (cv. Tendergreen) seeds was subjected to limited proteolysis with trypsin, chymotrypsin, papain, proteinase K and protease V8, and to cleavage with cyanogen bromide and 2-(2-nitrophenylsulfanyl)-3-methyl-3''-bromoindolenine. Mapping of peptides separated from each of the 3 G1 subunits by polyacrylamide gel electrophoresis revealed that many proteolytic cleavage sites were present at similar positions on the subunits. The G1 subunits are homologous in amino acid sequence for about 61% of their length. The remaining region (possibly COOH-terminal) of the subunits appears to be heterologous, with the .alpha. subunit bearing an additional methionine residue.