Lactose galactose metabolism

Bissett, D.L. Anderson, R.L. Lactose and D-galactose metabolism in Staphylococcus aureus. Ill Purification and properties of D-tagatose-6-phosphate kinase. J. Biol. Chem., 255, 8745-8749 (1980)... 

Bissett, D. L. and Anderson, R. L. 1973. Lactose and D-galactose metabolism in Staphylococcus aureus Pathway of D-galactose 6-phosphate degradation. Biochem. Bio-phys. Res. Commun. 52, 641-645. 

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. 

The metabolism of lactose and lactate in Swiss-type cheeses was described comprehensively by Turner et al. (1983). Typically, Emmental cheese contains 1.7% lactose 30 min after moulding, which is rapidly metabolized by 5. thermophilus with the production of L-lactate. Only the glucose moiety of lactose is metabolized by S. thermophilus and consequently galactose accumulates to a maximum of —0.7% at —10 hr, when the lactobacilli begin to multiply. These metabolize galactose to a mixture of d- and L-lactate, which reach —0.35 and 1.2%, respectively, at 14 days, when the galactose is metabolized completely. 

The disorders of galactose metabolism are commonly detected by neonatal screening. Symptoms occur following the ingestion of lactose/galactose-containing formulas. 

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. 

Bisset DL, Anderson RL (1974) Lactose and D-galactose metabolism in group N-streptococci presence of enzymes for both the D-galactose-1-phosphate and d-tagatose-6-phosphate pathways. J Bacteriol 117(1) 318-320... 

Galactose, a constituent of the disaccharide lactose found in dairy products, is metabolized by a patiiwav that includes the isomerization of UDP-galactose to UDP-glucose. where UDP = uridylyl diphosphate. The enzyme responsible for the transformation uses NAD+ as cofactor. Propose a mechanism. 

D-Galactose Hydrolysis of lactose. Can be changed to glucose in the liver and metabolized. Synthesized in the mammary gland to make the lactose of milk. A constituent of glycolipids and glycoproteins. Failure to metabolize leads to galactosemia and cataract. 

The pentose phosphate pathway is an alternative route for the metabolism of glucose. It does not generate ATP but has two major functions (1) The formation of NADPH for synthesis of fatty acids and steroids and (2) the synthesis of ribose for nucleotide and nucleic acid formation. Glucose, fructose, and galactose are the main hexoses absorbed from the gastrointestinal tract, derived principally from dietary starch, sucrose, and lactose, respectively. Fructose and galactose are converted to glucose, mainly in the liver. 

The main gene, lacX, encodes (J-galactosidase, which hydrolyzes the disaccharide lactose to glucose + galactose to begin their metabolism. 

The ability to metabolize galactose decreases on ageing (after 70 years), leading to cataract perhaps this, together with the fact that mammals normally encounter lactose only while suckling, explains why many people lose the ability to utilize lactose at the end of childhood. 

Figure 10.12 Metabolism of lactose by lactic acid bacteria many Lactobacillus species/strains can not metabolize galactose (from Cogan and Hill, 1993).

Figure 10.15 Metabolism of lactose, glucose, galactose, d- and L-lactic acid in Emmental cheese. Cheese transferred to hot room (22-24°C) at 14 days. , D-lactate O, acetate , galactose , L-lactate , glucose 0 lactose , propionate.

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