Polygalacturonase inhibitors in bean pods.

The amount of polygalacturonase-inhibiting protein (PGIP) was 14 times higher in bean pods than in etiolated hypocotyls. The PGIP was extracted from bean pods and partially purified by chromatography on columns of S-Sepharose. DEAE-Sephadex A-50, and Sephadex G-75. Further purification by ion-exchange chromatography on a Mono Q column separated two isoforms of the inhibitor. The two PGIPs were similar in most properties but differed slightly in pI values. They also differed in one residue of the N-terminal amino acid sequences. Both bean pod PGIPs differed in two and possibly three residues of the deduced N-terminal amino acid sequence for hypocotyl PGIP. Small alterations in the structure of PGIP may represent a strategy in bean plants for resistance to a variety of pathogens.