Heterogeneity of alkaline small subunits of ribulose 1,5 bisphosphate carboxylase-oxygenase from Medicago sativa and M. falcata.

The isolated leaf proteins of lucerne (Medicago sativa L. and M. falcata L.) were fractionated by Sepharose 6B column chromatography. Analysis of fractionated proteins indicated that the 2nd peak component was almost entirely ribulose 1,5 bisphosphate carboxylase-oxygenase (Rubisco) which represented 57% of the total recovered protein.Rubisco yielded one large subunit (LSU) and one small subunit (SSU) polypeptide after SDS gel electrophoresis.Isoelectric focusing of the SSU of Rubisco from genotypes of M. sativa cv. Hunter River (HR), Hairy Peruvian (HP) and of M. falcata (MF) showed two SSU components for HR and HP, and three components for MF. Most components of genotypes were located in the alkaline region of the gel. While the pIs of the SSU components of HR and HP were identical they differed from those of the SSU of MF thus demonstrating heterogeneity for SSU in Medicago.It is suggested that the alkaline nature of SSU may have some adaptive physiological significance.