Enzyme stimulation

Barley is often considered to be somewhat prophylactic with regards to digestive disorder in piglets. This seems to be accentuated by including enzymes. This is presumably due to the enzymes stimulating digestion in the upper sections of the intestinal tract, which in trrm reduces readily available substrate for bacterial proliferation in the lower tract. 

Mertens E, Van Schaftingen E, Muller M (1992) Pyruvate kinase from Trichomonas vaginalis, an allosteric enzyme stimulated by ribose 5-phosphate and glycerate 3-phos-phate. Mol Biochem Parasitol 54 13-20... 

McCormack KM, Kluwe WM, Rickert DE, et al. 1978. Renal and hepatic microsomal enzyme stimulation and renal function following three months of dietary exposure to polybrominated biphenyls. Toxicol Appl Pharmacol 44 539-553. 

Hen egg white lysozyme is a small protein of Mr 14 500 and 129 amino acid residues. This enzyme was introduced in Chapter 1, where it was pointed out that examination of the crystal structure of the enzyme stimulated most of the solution studies. Hen egg white lysozyme has the distinction of being the first enzyme to have had its structure solved by x-ray crystallography.207 It is an atypical member of the hexosaminidase class of glycosyl transfer enzymes. It catalyzes the hydrolysis of substrates with retention of stereochemistry. T4 lysozyme was for many years thought to have the same fold and mechanism of lysozyme, despite there being no sequence homology. But it has now been found that the T4 enzyme has inversion of configuration and so operates by a different mechanism.208,209 A mechanism proposed for the enzymatic reaction was based on the structure of the... 

Long-term anticonvulsive therapy with diphenylhydantoin or phenobarbital is known to cause osteomalacia by influencing calcium metabolism (24,25). Alteration in the metabolism of vitamin D, presumably secondary to induction of hepatic microsomal enzymes, leads to the calcium and bone abnormalities (26). Patients on anticonvulsive therapy with phenytoin exhibit a decrease in serum 25-hydroxyvitamin D (27). Adequate dietary amounts of vitamin precursors or microsomal enzyme stimulators might prevent these effects of long-term therapy. 

Type II deiodinase activity is low in unsupplemented tissue homogenates but is stimulated by DTT [71-74,82,83] and to a lesser extent also by GSH [72]. The DTT concentrations required for maximal enzyme stimulation in the CNS and pituitary seem higher than in BAT and also than those necessary for the type I deiodinase in liver and kidney. Kinetic analysis of the deiodination of varying substrate (T4, rT3) concentrations at different cofactor (DTT) levels have indicated a sequential reaction mechanism for the type II deiodinase [73,82,83]. This is very suggestive of the formation of a ternary enzyme-substrate-cofactor complex in the catalytic process [82], The physiological cofactor of the type II deiodinase has not been identified but it has been observed that GSH depletion with diamide or diethylmaleate impairs T4 to T3 conversion in GH3 pituitary tumor cells [93]. 

JJ Bums, AH Conney. Clinical effects of interaction between drugs. Enzyme stimulation and inhibition in the metabolism of drugs. Proc R Soc Med 58 955, 1965. 

I. Insulin-dependent Enzyme Stimulants Inositolphosphoglycan Mimics... 

Enzyme induction can be problematic with co-administration of benzodiazepines and rifampicin or certain anticonvulsants (phenobarbital, phenytoin, carbamaze-pine). However, despite enzyme stimulation, the net effect of adding these anticonvulsants can be augmentation of benzodiazepine-induced sedation. 

Addition of microorganisms and enzymes stimulates the biodegradation of xenobiotics in soils. Most efforts have been directed toward the use of bacterial inocula grown in large fermenters for the bioremediation of soils contaminated with PCP. Also, microbial immobilization on bark chips or their encapsulation in polyurethane or alginate, enhances their PCP-degrading ability as well as their resistance to PCP toxicity. 

FUNCTION Stimulates pancreatic secretion of enzymes stimulates gallbladder contraction. Has other effects in ways similar to gastrin and secretin. 

The mechanism by which the action of a hormone on its tissue receptor leads to stimulation of adenylate cyclase is not known. Studies concerning the relationship of hormone binding to enzyme stimulation are in their infancy, and there may not be a direct relation between the number of receptors occupied and the extent of enzyme stimulation. The problems involved in the identification of the glucagon [24] and catecholamine receptors [25-27] have been discussed elsewhere. 

There are metabolic differences between the sexes. Many barbiturates induce more prolonged sleep in female rats than in males. The shorter duration of action of hexobarbital in male rats is related to the higher activity of the liver microsomal enzymes stimulated by testosterone to hydroxylate this chemical. This higher activity can be reduced by castration or pretreatment with estrogen (female hormone). 

A new type of glucosylceramidase cofactor has recently been described by Vaccaro et al. (1985). This protein, which seems to be tightly associated with the enzyme, stimulates the hydrolysis of glucosylceramide but not that of the water-soluble substrate. Similarly two small proteins that stimulate specifically lysosomal sphingomyelinase were recently observed by Christomanou and Kleinschmidt (1985). In both cases it is, however, still too early to speculate on the role and significance of these proteins. 

Cell division was arrested with cytosine arabinoside to avoid the problem of receptor expression in the products of mitosis during the course of the experiment. It is quite apparent that resensitization of desensitized cells occurs in the absence of carbacyclin, and in further experiments (data not shown) the resensitization was shown to be dependent on de novo protein synthesis. There was no resensitization in the presence of cycloheximide or actinomycin D (an inhibitor of transcription). It is of particular significance that, when cells were desensitized and then allowed to resensitize, the synthesis of new receptor was accompanied by a restoration of the capacity for enzyme activation, and also by a return to the relatively high-affinity for enzyme stimulation (Figure 8.21). 

Aktories, K., Schultz, G. and Jacobs, K.H. (1981). The hamster adipocyte adenylate cyclase system. II. Regulation of enzyme stimulation and inhibition by monovalent cations. Biochim. Biophys. Ada, 676, 59-67... 

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