In unripe banana pulp, P31 accounts for approximately 20-30 percent of the total soluble pulp protein. Storage proteins are broken down during a subsequent developmental stage. P31 is broken down during banana ripening. Storage proteins are generally localized in storage vacuoles within the cell. P31 is localized there.
Storage proteins contain a large proportion of particular amino acid residues.
Storage proteins typically lack any other metabolic or structural role in the organism. Some retain a little enzymatic activity, but this could not be the case for the banana protein, which has only three of the five amino acids required. We suspect that P31 serves as a storage protein in banana. Experiments are in progress to determi ne whether a P31- promoting element that we have introduced into tomato plants by genetic manipulation will prove to be related to fruit ripening in the tomato, supporting our view of the role of P31. Our studies may prove to be valuable for Boyce Thompson research on edible vaccines because storage protein-promoting elements might be genetically manipulated to assist in delivering the vaccine.