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Reactions of benzylamines with methylamine dehydrogenase

Reactions of benzylamines with methylamine dehydrogenase. Evidence for a carbanionic reaction intermediate and reaction mechanism similar to eukaryotic quinoproteins. Davidson, Victor L.; Jones, Limei Hsu; Graichen, M. Elizabeth (Med. Cent., Univ. Mississippi, Jackson, MS 39216-4505, USA). 7409-30-5 and 60496-14-2 are also occured in this study. Biochemistry, 31(13), 3385-90 (English) 1992. CODEN: BICHAW. ISSN: 0006-2960. DOCUMENT TYPE: Journal CA Section: 7 (Enzymes) It was previously reported that arom. amines were not substrates for the bacterial quinoprotein, methylamine dehydrogenase (I). Here, benzylamine-dependent activity was also not obsd. in the steady-state assay of Paracoccus denitrificans I with the artificial electron acceptor, phenazine ethosulfate (PES). Benzylamines did, however, stoichiometrically reduce the protein-bound tryptophan tryptophylquinone (TTQ) prosthetic group and acted as reversible competitive inhibitors of methylamine oxidn. when I was assayed with PES. When I activity was monitored using a steady-state assay which employed its physiol. electron acceptor, amicyanin, instead of PES, very low but detectable benzylamine-dependent activity was obsd. The reactions of a series of para-substituted benzylamines with I were examd. A Hammett plot of the log of Ki values for competitive inhibition by these amines against sp exhibited a neg. slope. Rapid kinetic measurements allowed the detn. of values of k3 and Ks for the redn. of TTQ by each of these amines. A Hammett plot of log k3 vs. sp exhibited a pos. slope, which suggested that the oxidn. of these amines by I proceeds through a carbanionic reaction intermediate. A neg. slope was obsd. for the correlation between log Ks and sp. Plots of log k3 and log Ks against substituent consts. which reflected either resonance or field/inductive parameters for each para substituent indicated that the magnitude of k3 was primarily influenced by field/inductive effects, whereas ks was primarily influenced by resonance effects. No correlation was obsd. between either k3 or Ks and the relative hydrophobicity of the para-substituted benzylamines or steric parameters. The Ki values which were obtained from steady-state kinetic expts. correlated strongly with the Ks values which were obtained from rapid kinetic expts. On the basis of these results, a mechanism was proposed for the reactions of benzylamines with this enzyme. These data were also discussed in light of results of similar studies of the reactions of para-substituted benzylamines with 2 eukaryotic quinoproteins, lysyl oxidase and plasma amine oxidase. .

Intramolecularly quenched fluorescent substrates for aspartic proteinases

Intramolecularly quenched fluorescent substrates for aspartic proteinases. Filippova, I. Yu.; Lysogorskaya, E. N.; Oksenoit, E. S.; Komarov, Yu. E.; Stepanov, V. M. (Chem. Dep., M. V. Lomonosov Moscow State Univ., Moscow, USSR). Bioorg. Khim., 12(9), 1172-80 (Russian) 1986. CODEN: BIKHD7. DOCUMENT TYPE: Journal CA Section: 7 (Enzymes) o-Aminobenzoyl tetrapeptides of the structure, Abz-Ala-Ala-Phe-Phe-B [where Abz is o-aminobenzoyl and B is p-nitroaniline (pNA), 2,4-dinitrophenylethylenediamine (Ded), or p-nitrobenzylamine (Nba)], were prepd. by a combination of chem. and enzymic methods. The design of these peptides relied on the principle of intramol. fluorescence quenching. Pepsin and aspergillopepsin A hydrolyzed the Phe-Phe bond of the substrates, Abz-Ala-Ala-Phe-Phe-Ded, Abz-Ala-Ala-Phe-Phe-pNa, Abz-Ala-Ala-Phe-Phe-Nba, with an increase in fluorescence of 8.There are some commonly used reagents with their cas registry numbers 7409-30-5 and 106077-00-3 in this article.5-, 4.5-, and 2.5-fold, resp., upon hydrolysis. Kinetic parameters for the enzymic hydrolysis of the substrates were detd. The proteolysis coeffs. for the synthetic substrates were comparable to the kcat/Km values (where kcat is the catalytic rate const.) for the best substrates of aspartic proteases previously reported. .