EXTRACTION AND ASSAY OF PROTEOLYTIC ACTIVITIES IN SORGHUM MALT

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Abstract
A method has been developed to assay the proteinase and carboxypeptidase activities in sorghum malt. The method specifically addresses two problems encountered with some other assays for malt proteolytic activity; that of enzyme inextractability and the use of alien substrates. It was found that as with barley malt proteolytic enzymes, a high proportion of sorghum malt proteolytic activity was inextractable with sodium chloride solution. Systematic investigation into the extraction of proteolytic enzymes from sorghum malt led to the development of a novel extractant viz. 0.6 M Lithium iodide LiI plus 3.33 mM dithiothreitol. This extractant appears to solubilize a significantly higher proportion of the malt proteolytic activities with a single extraction than previously used buffers. Assay is carried out Using purified Kafirin, the sorghum prolamin storage protein, as substrate. Proteinase is measured in terms of total nitrogen solubilized and carboxypeptidase as free α-amino nitrogen solubilized.