Biochemical and physiological studies of soybean β-amylase.

Abstract Soybean ( Glycine max L. Merr.) seed β-amylase has been identified among the ethanol-soluble proteins, purified and several cDNA clones isolated [Ren et al. (1993) Phytochemistry 33, 535]. Both soybean and barley ( Hordeum vulgare L.) β-amylases were soluble in ethanol solutions up to 60%. The solubility of the enzyme decreased with increasing ethanol concentration and dropped sharply between 50 and 60% ethanol. The results showed that β-amylase is an enzyme which can tolerate extensive ethanol treatment at room temperature without losing activity. In soybean seeds, β-amylase appeared to be located neither in protein bodies nor in a membrane fraction. The β-amylase accumulated in the developing seed and disappeared from the germinating cotyledons at a rate similar to that of the total seed protein. Soybean β-amylase was resistant to digestion by some proteases, such as trypsin, chymotrypsin and a protease from Staphylococcus aureus V8. Very little of the total amylase activity in soybean leaves and roots was ethanol soluble. In eight other legume seeds tested, amylase activity was very low compared to the activity present in soybean seeds.