Isoelectric fractionation and some properties of a protease from soyabean seeds

A protease, capable of hydrolysing benzoyl DL‐arginine p‐nitroanilide(BAPA), and L‐amino acid β‐naphthylamide derivatives, was purified, by isoelectric focusing in the region pH 3–6, from dormant and 6‐day germinated soyabean seeds. The enzyme was focused at pH 4·80. The Km value using BAPA as substrate was found to be 5·03 × 10−4M. Maximum activity of the enzyme towards BAPA was obtained in the pH 8·2–8–5 region. Slight activation was observed in the presence of 0·05 M concentration of Ca2+ and Mg2+ ions. The protease lacked caseinolytic activity, and was not inhibited by Kunitz soyabean trypsin inhibitor.

Spectroscopic studies on the conformation of native and denatured glycinin

Optical rotatory dispersion (ORD) studies and infrared spectra in deuterium oxide indicate that native glycinin exhibits mainly a β‐conformation structure. Ultraviolet difference spectra showed that urea ami guanidine hydrochloride at increasing concentrations cause progressive exposure of tyrosine and tryptophan residues. Ultraviolet difference spectroscopy was also used in following the course of acid‐induced denaturation of glycinin. It was observed that acid denaturation starts approximately at pH 3.50 reaching a maximum at pH 2.0. Data obtained by solvent perturbation of native glycinin using perturbants exhibiting mean diameters of 2.0, 4.4, and 7.2 A indicate that approximately 34 to 37 residues (45%of the total) are accessible to these perturbants whereas the accessibility of tryptophan residues is decreased with increasing mean diameters of the perturbant.