The basic amino-acids of leaf proteins. With a discussion of various methods of analysis

Abstract

Block''s (1934) small-scale adaptation of the Vickery method for the estimation of the basic amino-acids of proteins has been investigated in detail. Certain minor modifications are recommended, and the modified procedure has been tested against appropriate mixtures of bases to obtain some idea of the corrections to be applied for arginine silver and overall losses. Various standard proteins have been analysed by this modified procedure and, after correction, the results compare favorably with those obtained by Vickery and his co-workers. A general criticism has been made of certain direct and indirect methods of base analysis. Hydrolysis of the 3 individual bases in the presence of various fur-furaldehyde-yielding carbohydrates has shown that arginine suffers a loss which is roughly proportional to the amount of carbohydrate present, that histidine recoveries may be irregular and that lysine recoveries are normal unless a large excess of carbohydrate is present. In the light of these results it has been possible to obtain fairly satisfactory analyses for all 3 bases of leaf protein preparations containing from 12 to 16% N. Leaf material relatively poor in protein (containing less than 8% protein-N) requires special preliminary treatment, and it is considered that the only base which can be estimated with any reliability is lysine. In keeping with the previous analyses for certain other amino-acids and the amide-N by Lugg, the base analyses of leaf proteins exhibit but little variation from species to species and within a single species with season.