Studies on the purification and characterisation of the major albumin seed proteins from pea (pisum sativum L.)

PLA does not contain methionine, but contains a relatively high-level of cysteine (4 residues per polypeptide) suggesting a possible role as a sulphur storage protein. However, its sequence is not homologous to low Mr (2S) storage proteins from castor bean (Ricinus communis) or rape (Brassica napus); PLA therefore represents a new type of low Mr seed protein. The putative storage role of PMA and PLA is not supported by studies on germinating seeds which show that PMA-L, PMA-S and PLA are not significantly degraded. on or after germination during the period in which the major globulin fraction storage proteins are utilised. It is possible that these proteins have no significant role in seed physiology, since a few different pea lines are shown to lack either PMA-L, PMA (L + S), or other proteins of the albumin solubility fractions, although none lack PLA. Further evidence for the non-functional role of PMA is provided by its species distribution; preliminary screening indicates the presence of homologous major albumin proteins only in closely related legume species.