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Inactivation of pancreatic and gastric lipases by tetrahydrolipstatin and alkyl-dithio-5-(2-nitrobenzoic acid). A kinetic study with 1,2-didecanoyl-sn-glycerol monolayers.

We studied the covalent inhibition of lipases by the monolayer technique. We report the inactivation of porcine pancreatic and human and rabbit gastric lipases, acting on mixed monomolecular films of dicaprin containing tetrahydrolipstatin or new hydrophobic disulfide compounds, which can be described as a 'poisoned-interface' system. A kinetic model is presented for depicting the covalent inactivation of lipolytic enzymes at a lipid/water interface. The stoichiometry of the interfacial situation can be described as follows: one lipase molecule embedded among 10(5) substrate molecules will be inactivated to half its initial velocity by the presence of 10 tetrahydrolipstatin molecules. This inactivation was independent of the surface pressure. When tested in the form of mixed films, all the disulfide compounds investigated specifically reduced the hydrolysis of 1,2-didecanoyl-sn-glycerol films by gastric lipases, but did not affect hydrolysis by pancreatic lipase. With this poisoned-interface system, tetrahydrolipstatin was found to be the most potent inactivator, whereas disulfide compounds showed a higher degree of selectivity than tetrahydrolipstatin.

Animals↗

The effect of flavins and enzyme inhibitors on 4-nitrobenzoic acid reductase and azo reductase of Ascaris lumbricoides var suum.

1. The effects of inhibitors and activators on the azo- and nitro-reductases of Ascaris lumbricoides var suum have been investigated. Both types of reduction were inhibited by FAD, FMN, riboflavin, allopurinol, dicoumarol, 5-nitro-2-furaldehyde, azide and cyanide at concentrations of 1 mM. Neither reaction was inhibited by menadione, nitrofurantoin, SKF 525-A or fluoride. Both reactions were stimulated by addition of hypoxanthine. 2. The enzyme preparation contained no detectable aldehyde oxidase or xanthine oxidase activity. 3. The differences in the effects of flavins and inhibitors on mammalian and nematode azo- and nitro-reductases might have practical significance in the development of anthelmintic synergists.

Aldehydes↗