Hydroxylamine enzyme interactions

Based upon studies involving the interaction of 6-acetylmethylenepenicil-lanic acid (27) with TEM-1 yff-lactamase, as well as its chemical reactivity with sodium methoxide and hydroxylamine, Arisawa and Adam [45] proposed a mechanism for the inhibition of TEM-1 )8-lactamase by (27) Scheme 6.10). They proposed the initial formation of a rather stable inactivated enzyme (55). This was followed by either slow hydrolysis of the acyl bond, releasing active enzyme, or rearrangement to (56). The stability of this intermediate was explained on the grounds of its pyrrolic structure the conjugated ester behaves as a vinylogous urethane, which is known to be resistant to hydrolysis [72]. 

The nitrite reductase system of Achromobacter fischeri appears to be composed of two separable enzymes 341). The first enzyme is a flavin reductase and utilizes NADH or NADPH to reduce FMN or FAD. The second interacts with the flavin reductase and converts nitrite and hydroxylamine to ammonia. The nitrite reductase enzyme has a molecular weight of 95,000 4,000 (Table XVII), contains two heme c per mole, and is inhibited by p-mercuribenzoate, cyanide, and carbon monoxide. 

Because many drugs contain either chiral centers, prechiral centers, or both, interest in stereochemical substrate-enzyme interactions, the stereospecificity of biotransformations, and species (and strain) differences in these parameters is increasing. Since enzymes themselves contain chiral centers, differential interaction of R and S isomers of drugs with drug metabolizing enzymes is the rule rather than the exception. Beckett reported stereoselectivity in the N-dealkylation, deamination, and formation of the nitrone and secondary hydroxylamine metabolites (+) -and (-) - N-benzylamphetamine ( ) in rabbits. Stereoselectivity has also been observed in the dealkylation of d-, 1-, and d,1-fenfluramine (22), an anorexiogenic agent. 

Fig. 7. (A) Flash-induced absorption-change pattern of neutral red in dark-adapted thylakoids in the absence and in the presence of hydroxylamine. (B) relative yield of proton release (measured by the magnitude of 4-ms rise component of 4A) in thylakoids in the presence of hydroxylamine solid dots, experimental values derived from (A) open circles for calculated values. See text for discussion. Figure source FOrster and Junge (1985) Interaction of hydroxylamine with the water-oxidizing enzyme investigated via proton release. Photochem Photobiol 41 192...

V F rster and W Junge (1985) Interaction of hydroxylamine with the water-oxidizing enzyme investigated via proton release. Photochem Photobiol 41 191-194... 

When the co-enzyme is attached to the active centre of the enzyme, the rates of formation and breakdown of Schiff bases may differ from those observed with free co-enzyme. This is because the co-enzyme may already be present as a Schiff base at the active centre of the enzyme [Figure and also because interaction of the amino compound with the apo-enzyme may alter the rate constants. Inhibition of pyridoxal phosphate-dependent enzymes by reagents such as hydroxylamine or semicarbazide depends on the high affinities of these reagents for the aldehyde group of the co-enzyme. However, as Schiff base formation is readily reversible, this type of inhibition is easily reversed also. 

McDermott et al. (163) have proposed that there are two groups of substrates for ceruloplasmin those substances for which non-chelated Fe is not required and therefore which interact directly with the enzyme and those substrates which require the presence of non-chelated Fe to be catal3dically oxidized. Some substrates belonging to the former group are epinephrine, PPD, norepinephrine, dopamine, and serotonin. Those falling in the second class are ascorbate, hydro-quinone, ferrocyanide, L-DOPA, hydroxylamine, thioglycolic, acid and cysteine. 

The hydroxylamines of both 21 and 22 interact with the catalytic zinc of the enzyme and the amides of 21 and 22 form a hydrogen bond with an aspartic... 

The B2 protein contains 2 moles of non-heme iron per molecule of enzyme. The iron is bound tightly, but can be removed by dialysis against 8-hydroxyquinoline. The iron-depleted enzyme is inactive, but activity may be restored by addition of iron. The B2 protein has a characteristic absorption peak at 410 m/i, which is attributed to its iron content. Hydroxyurea, which is known to inhibit DNA biosynthesis, evidently achieves this effect through interaction with the B2 protein (7). When the B2 protein is treated with hydroxyurea, the characteristic absorption at 410 m/t disappears, and the resulting loss of enzyme activity parallels the decrease in absorbance at that wavelength. Similar effects are obtained with hydroxylamine or hydrazine. 

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