Sucrose-phosphate synthase from wheat. Characterization of peptides by immunoblotting analysis

Abstract

The structure of sucrose-phosphate synthase (SPS: EC 2.4.1.14) from wheat (Triticum aestivum L. cv. San Agustin was studied using antibodies prepared against the enzyme purified from wheat germ. The antibodies revealed the presence of 55 and 35 kDa polypeptides in wheat germ, endosperm, embryos and whole seed, while in whole wheat leaf, a 90 kDa was detected. It is not clear whether the 35 and 55 kDa polypeptide are truly subunits of SPS or they are the product of protease action, more active in non-photosynthetic tissues than in leaves. The antibodies from wheat germ clearly recognized polypeptides in leaf protein preparations from other plants (barley, soybean, maize) and, weakly in others (peanut, tobacco). It did not recognize any polypeptide in spinach and mustard leaf extracts. In the case of maize leaf, a peptide of higher molecular mass (116 kDa) than the wheat ones was revealed. The results may indicate the presence of different polypeptide compositions for sucrose-phosphate synthase, and suggest the existence of at least two types of this enzyme.