Glucosidase enzymes

Figure 21. Double-reciprocal plot of Bis-Tris inhibition of debranching enzyme glucosidase activity using glucose-14C assay (39)...

Letter for Doctors Patients. The theory is that there are two chemicals called quinones occurring in wheat germ that are liberated by the action of the yeast enzyme glucosidase and which chaperone cellular metabolism, thereby countering the hypermetabolism of cancer cells, in the process serving as anticancer agents or at least modulating the adverse side effects of chemotherapy. 

The first results showing this type of discontinuous enzyme synthesis in E, coli were obtained by Masters and co-workers (1964), who found that different enzymes of E. coli double their activity at different moments of the cell cycle. In experiments by Halvorson and co-workers (Halvorson et al., 1964 Gorman et al., 1964), a series of enzymes (glucosidase, invertase, alkaline phosphatase) was studied from this point of view in synchronized cultures of different species of yeasts. The "jumps in activity of the different enzymes occurred at different points of the cycle, and the experiments showed that in Saccharomyces cerevisiae there are two structural genes for alkaline phosphatase and invertase (two periods of synthesis during the cycle). 

Hydrolases. Enzymes catalysing the hydrolytic cleavage ofC —O, C —N and C —C bonds. The systematic name always includes hydrolase but the recommended name is often formed by the addition of ase to the substrate. Examples are esterases, glucosidases, peptidases, proteinases, phospholipases. Other bonds may be cleaved besides those cited, e.g. during the action of sulphatases and phosphatases. 

The first member of this class, acarbose, was introduced in the early 1990s. a-Glucosidase inhibitors slow the intestinal process of carbohydrate digestion by competitive inhibition of the activity of a-glucosidase enzymes located in the brush border of the enterocytes... 

A straightforward discrimination between the two pathways is possible with enzymes that are inhibited by basic glycosyl derivatives as well as by permanently cationic ones. This is illustrated by )S-D-glucosidase A3 from Asp. wentii, where K4 values for yS-D-glucosylpyridinium ion, / -D-glucosyla-... 

The type of intermediate that is formed in the slow inhibition with D-gly-cals was identified, with the aid of the ) -D-glucosidase A3 from Asp. wentii, as an ester of 2-deoxy-D-araA/ o-hexose with an aspartic acid side-chain. The same aspartoyl residue had already been shown, by labeling with con-duritol B epoxide (see Section 111,1), to be essential for -D-glucoside hydrolysis. In addition, this aspartate was found to form a glycosyl -enzyme... 

Scheme 3.—Formation of 2-Deoxy-a-D-arahino-hexosyl Enzyme from D-Glucal at the Active Site of a )3-D-Glucosidase.

---