Biochemical studies of protein bodies isolated from Lupinus angustifolius cotyledons confirmed that they contained storage protein along with lower levels of carbohydrate, lipid reserves and high activities of several hydrolytic enzymes. Two forms each of alpha-D-galactosidase and alpha-D-mannosidase were isolated from the protein body and substantially purified. The enzymes resembled other seed mannosidases and galactosidases in substrate specificity, MW, sensitivity to pH and inhibitors, and their kinetic and thermodynamic behaviour. Mannosidase was also capable of hydrolysing the oligosaccharide moieties of the protein body glycoprotein a conglutin, and galactosidase was able to hydrolyse the raffinose series oligosaccharides found in the organelle. A role of these enzymes in glycoprotein and/or galactoside mobilization is suggested. Intact protein bodies were easily isolated from unimbibed tissue but attempts to disrupt and sub fractionate the preparation, thereby releasing the limiting membrane failed due to the presence of a high MW glutelin protein fraction which was insoluble except at extremely high pH. The fragility of protein bodies isolated from imbibed tissue and the increased solubility of their matrix proteins facilitated the disruption and subfractionation of the organelle. A putative protein body membrane fraction was separated from this and found to contain a detergent soluble, cation stimulated NADH cytochrome c reductase. The possibility of this activity arising from microsomal or mitochondrial contamination was considered but the results of enzyme marker and inhibitor studies suggested that the activity occurred at the protein body membrane. A preliminary study of the properties of the reductase indicated that it was more closely related to the microsomal redox assembly than that of mitochondria thus supporting the established view of protein body ontogenesis from the ER. Activity modulator studies of the reductase suggested it might have a role in trans-membrane proton and/or solute transport during germination.
|Date of Award||1982|