Subunit structure and immunological properties of wheat carboxypeptidase

Abstract Wheat carboxypeptidases I, II, III and IV from wheat seeds with isoelectric points of 4.8, 5.6, 6.0 and 6.5, respectively, were found to be homogeneous by the Ouchterlony double immunodiffusion technique using an antiserum of the enzyme III. In a previous paper [1], the native enzyme III (MW = 118 k) was separated into two 58 k subunits (MW = 58 k) and further divided into the 35 k and 25 k fragments (MW = 35 k and 25 k, respectively). The native enzyme III and the 58 k subunit produced a single precipitin line against the antiserum. The 35 k and 25 k fragments did not cross-react with the antiserum. The amino acid compositions of the 35 k and 25 k fragments were similar to each other. Amino-terminal amino acids of the 35 k and 25 k fragments were both glutamic acid. Carboxy-terminal groups of the 35k and 25k fragments were determined to be -(Gly, Ser)-Glu-OH and -Thr-Pro-Glu-OH, respectively. The Ouchterlony double immunodiffusion technique revealed the presence of a common antigen in a carboxypeptidase from wheat seeds and one from germinated wheat. Comparison of both enzymes is discussed.