Galactose metabolizing enzymes

Segal and Blair (S13) have shown that aldehydes reduce NAD to NADH2 in the presence of aldehyde dehydrogenase progesterone, menthol, and menthone inhibit this enzyme and this may account for the stimulatory action shown by these substances on galactose metabolism in vitro. 

Bissett, D. L. and Anderson, R. L. 1974B. Lactose and D-galactose metabolism in Group N streptococci Presence of enzymes for both the D-glactose 1-phosphate and d-tagatose 6-phosphate pathways. J. Bacteriol 117, 318-320. 

In the induction of enzymes of galactose metabolism in E. coli, three enzymes are involved -galactosidase (which catalyses the hydrolysis of the y -glycosidic bonds of lactose), galactose permease (which is responsible for transport of lactose across the cell membrane) and a third enzyme, A-protein, apparently not directly involved in galactose metabolism. The system has an environmental inducer, galactose, and in its presence the number of /)-galactosidase molecules rises from 5-10 to 10,000 within the cell. The addition of the inducer can increase the protein production in less than five minutes after its addition. Protein synthesis of these enzymes stops almost immediately in the absence of lactose. 

This reaction is important in glycogen biosynthesis and galactose metabolism. The enzyme is composed of two polypeptide chains, labelled A and B. 

Another enzyme important to galactose metabolism, at least in E. coli, is galactose mutarotase. ... 

In a manner similar to fmctose, some individnals have a genetic defect in one of the enzymes involved in galactose metaholism and consumption of galactose hy these individnals can be detrimental to their health. The most common defect in galactose metabolism is with galactokinase, and not with the epimerase. 

A. When a disorder in galactose metabolism is suspected, especially in GALT and GALE, elimination of dietary lactose/galactose from the diet shotild be initiated immediately even before the diagnosis is confirmed by enzyme assay and/or DNA analysis. 

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