Acts as a membranotoxin, probably through its antibacterial and antifungal activities, contributing to the defense mechanism of the plant against predators. Forms monovalent cation-selective ion channels in membranes. Has antibacterial activity against the Gram-positive bacteria S.aureus and C.michiganensis, and the Gram-negative bacteria E.coli, P.syringae pv phaseoli, A.tumefaciens and E.carotovora subsp carotovora. Acts synergistically with PINA against bacteria. Contributes to grain texture and hardness. Endosperm and aleurone layer of developing kernels. In the aleurone layer, mainly localized to starch granules and the surface of the plasma membrane, forming a uniform layer, also abundant in the intercellular space. In the endosperm, mainly localized to starch granules and the plasma membrane, but less abundant in the intercellular space. Not found in roots or coleoptiles. Starts to accumulate in seeds between 8 and 12 days after flowering. Levels increase markedly between 15 and 18 days after flowering, reaching a peak between 26 and 33 days after flowering. Levels then decline rapidly at none is detected at 40 days after flowering. Not detected in germinated seeds. Five disulfide bonds are present. In cv. Riband. In cv. Consort. In cv. Hereward. In cv. Hereward. In cv. Soissons. Variation in, or absence of, PINB is associated with variation in grain texture.