Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.4.3.13 (lysyl oxidase)
 1,248 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several methods have been used to study the distribution of the semicarbazide-sensitive amine oxidase (SSAO) within the wall of the rat aorta. After separation of the smooth muscle-containing layers of the tunica media from the connective tissue of the tunica adventitia, much higher specific enzyme activity (measured with 1 microM benzylamine) was found in homogenates of the media than of adventitia. Similar results were obtained for MAO-A (with 1 mM 5-HT as substrate). SSAO activity was also considerably higher in homogenates of cells (predominantly smooth muscle) isolated from medial tissue by enzymatic dissociation with collagenase and elastase compared with homogenates of cells (mostly of connective tissue origin) from the adventitia. Histochemical staining resulting from SSAO activity (with benzylamine as substrate) occurred predominantly and intensely over the tunica media in rat aortic sections, although some occasional staining of adventitial sites was also observed. Staining was prevented by the SSAO inhibitors hydroxylamine (1 microM) and semicarbazide (1 mM), but not by the MAO inhibitor, clorgyline (1 mM). These results indicate that SSAO is associated predominantly, although not exclusively, with the smooth muscle cells in the rat aorta. Our findings that beta-aminopropionitrile (BAPN) is a reversible, competitive inhibitor (Ki around 2 X 10(-4)M) of SSAO, in contrast to the irreversible inhibition of the connective tissue lysyl oxidase by BAPN reported by others, provides further evidence that these enzymes are not identical.
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PMID:Vascular smooth muscle cells: a major source of the semicarbazide-sensitive amine oxidase of the rat aorta. 286 84

The pH-dependent kinetics of lysyl oxidase catalysis was examined for evidence of an ionizable enzyme residue which might function as a general base catalyzing proton abstraction previously shown to be a component of the mechanism of substrate processing by this enzyme. Plots of log Vmax/Km for the oxidation of n-hexylamine versus pH yielded pKa values of 7.0 +/- 0.1 and 10.4 +/- 0.1. The higher pKa varied with different substrates, reflecting ionization of the substrate amino group. A van't Hoff plot of the temperature dependence of the lower pKa yielded a value of 6.1 kcal mol-1 for the enthalpy of ionization. This value as well as the pKa of 7.0 are consistent with those of histidine residues previously implicated as general base catalysts in enzymes. Incubation of lysyl oxidase with low concentrations of diethyl pyrocarbonate, a histidine-selective reagent, at 22 degrees C and pH 7.0 irreversibly inhibited enzyme activity by a pseudo first-order kinetic process. The inactivation of lysyl oxidase correlated with spectral and pH-dependent kinetic evidence for the chemical modification of 1 histidine residue/mol of enzyme, the pKa of which was 6.9 +/- 0.1, within experimental error of that seen in the plot of log Vmax/Km versus pH. Enzyme activity was restored by incubation of the modified enzyme with hydroxylamine, consistent with the ability of this nucleophile to displace the carbethoxy group from N-carbethoxyhistidine. The presence of the n-hexylamine substrate largely protected against enzyme inactivation by diethyl pyrocarbonate. These results thus indicate a functional role for histidine in lysyl oxidase catalysis consistent with that of a general base in proton abstraction.
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PMID:Evidence for a functional role for histidine in lysyl oxidase catalysis. 290 54