Lactose, function

Standards for dmg chemicals are pubUshed ia USP—NE. Dmg substances are chemicals that have therapeutic or diagnostic uses, whereas pharmaceutical iagredients provide preservative action, fiavoiing, or hilfillment of a function ia the formulation of dosage-form dmgs. Examples of dmg substances are acetaminophen [103-90-2] ampicillin [69-53-4] aspirin [50-78-2] powdered ipecac, riboflavin [83-88-5] staimous fluoride [7783-47-3] and thyroid. Examples of pharmaceutical iagredients are ethylparaben [120-47-8] lactose [63-42-3] magnesium stearate [557-04-0] sodium hydroxide [1310-73-2] starch [9005-25-8] and vanillin [121-33-5],... 

More than 30 years ago Jacob and Monod introduced the Escherichia coli lac operon as a model for gene regulation. The lac repressor molecule functions as a switch, regulated by inducer molecules, which controls the synthesis of enzymes necessary for E. coli to use lactose as an energy source. In the absence of lactose the repressor binds tightly to the operator DNA preventing the synthesis of these enzymes. Conversely when lactose is present, the repressor dissociates from the operator, allowing transcription of the operon. 

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. 

MacConkey s medium. This was introduced in 1905 to isolate Enterobacteriaceae from water, urine, faeces, foods, etc. Essentially, it consists of a nutrient medium with bile salts, lactose and a suitable indicator. The bile salts function as a natural surface-active agent which, while not inhibiting the growth of the Enterobacteriaceae, inhibits the growth of Gram-positive bacteria which are likely to be present in the material to be examined. 

Ovchinnikov 234 237) has shown that bovine rhodopsin, although quite different in amino acid sequence (348 residues), also forms seven transmembrane helices. This structural similarity between bacterial and mammalian light activated membrane proteins is remarkable. Since the two amino acid sequences have little in common it would appear that the necessary requirement is seven transmembrane helices to form a channel which is specific for proton migration. For example it has been suggested that a similar arrangement and function is performed by the lactose permease of E. coli237). 

Lactobacillus preparation is intended to replace colonic microflora. This supposedly restores intestinal functions and suppresses the growth of pathogenic microorganisms. However, a dairy product diet containing 200 to 400 g of lactose or dextrin is equally effective in recolonization of normal flora. 

Fig. 1. 100. Water content of 100 mg lactose at +25 °C as function of time. The vials have been closed with 13-mm stoppers of different pretreatment. Pretreatments SV1 steam-Sterilized U, untreated SV8, steam-sterilized followed by vacuum-drying of minimum 8 h. The lines are calculated by a model system (Fig. 4 from [1.87]).

The proteinuria and aminoaciduria, and acidosis and glucosuria where they occur, are probably caused by reversible inhibition of some functions of the renal tubule. There would appear to be no structural damage to the kidney. However, 2 children developed nephrolithiasis while being treated with a low-lactose diet (B7, C5), The time course of events, when galactose is withdrawn from and returned to the diet, suggests that some metabolite of galactose accumulates in the cells of the renal tubules and has an inhibitory effect on the reabsorption of a number of substances. 

Kaback H. R. (1998). Structure/function studies on the lactose permease of Escherichia coli, Acta Physiol. Scand. Suppl. 643, 163, 21-33. 

The same functions used in agriculture can be applied to processed foods. In baked goods, wheat gluten, various additives, starch damage, and water absorption are just some of the parameters measured [21-24]. Dairy products are also important and often analyzed by NIR. Moisture, fat, protein, lactose, lactic acid, and ash are common analytes in the dairy industry [25-28]. 

Fig. 2 Determination of Bt values (amount of functional immobilized ligand in the column) for the immobilized Erythrina cristagalli agglutinin. / -Nitrophenyl, (pNP)-lactose, diluted to various concentrations (8 to 50 pM), was used for concentration-dependence analysis. (A) The solid and dotted lines demonstrate elution profiles of pNP-lactose and control sugar (pNP-mannose), respectively. (B) Woolf-Hofstee-type plot was made by using V-V0 values. Adapted from 47 with permission.

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