Comparative studies on the inactivating enzymes for pyridoxal enzymes from yeast and rat

Nobuhiko Katunuma: an outstanding scientist in the field of proteolysis and warm-hearted 'Kendo Fighter' biochemist

Professor Nobuhiko Katunuma is well known for his outstanding contribution to the understanding of proteolysis in general and cysteine proteinases and their inhibitors in mammals. In fact, he is a world pioneer in the field. In 1963, he started his highly successful scientific career as a Professor at the Institute for Enzyme Research, the University of Tokushima. During the initial 30 years of his career, he was interested in vitamin B6 metabolism and discovered the acceleration of turnover rates of pyridoxal enzyme in apoprotein formation. After this period, his interest expanded to lysosomal cystein proteinases and their endogenous inhibitors. After determining the crystal structure of human cathepsin B, he generated a series of chemically synthesized specific inhibitors of cathepsins. These inhibitors are currently used throughout the world and some of them have been applied therapeutically in various diseases. During his career and even at present, Professor Katunuma has been studying Biochemistry in Medicine and also practicing to become a 'Kendo sword fencing Fighter'.

Isolation of a regulatory mutant of fructose-1,6-diphosphatase in Saccharomyces carlsbergensis

By selecting for growth on glycerol, but absence of growth on glucose, a mutant of Saccharomyces carlsbergensis was isolated which does not grow on glucose, fructose, mannose, or sucrose, which shows long-term adaptation to maltose, but which can grow normally on galactose, ethanol, or glycerol. In the mutant, fructose diphosphatase is not inactivated after the addition of glucose, fructose or mannose to the medium, resulting in the simultaneous presence of fructose diphosphatase and phosphofructokinase activity. Under these conditions, a cycle is probably catalyzed between fructose-6-phosphate and fructose-1,6-diphosphate, resulting in the net consumption of adenosine triphosphate and an immediate stop of protein synthesis.

Purification and properties of an inhibitor of the tryptophan-synthase-inactivating enzymes in yeast

An inhibitor of the tryptophan‐synthase‐inactivating enzymes has been isolated from bakers' yeast and purified 27‐fold on a protein basis, by heat treatment, precipitation by trichloroacetic acid, ethanol fractionation and acid precipitation. The inhibitory activity of the purified material is not affected by incubation with RNAase, DNAase, or muramidase, but is destroyed by incubation with pronase or trypsin. Inhibitory activity depends, therefore, on the protein content of the material.

The extent to which the inactivating enzymes are inhibited is proportional to inhibitor concentration. Tryptophan‐synthase inactivases I and II are both inhibited. The inhibitor appears to be specific in its action: it is much more effective than soybean trypsin inhibitor in inhibiting the inactivases, but has comparatively little effect on the esterolytic activity of trypsin.

Inhibitory activity was measured in crude extracts of Saccharomyces cerevisiae growing in batch culture. In the exponential growth phase, the inhibitor was barely detectable, but its levels subsequently rose at the end of the exponential phase and in the stationary phase. The possible biological significance of these observations is discussed.