Substrate (chemistry)

About: Substrate (chemistry) is a research topic. Over the lifetime, 35902 publications have been published within this topic receiving 740722 citations. The topic is also known as: enzyme substrate.

Purification and Properties of Flavin- and Molybdenum-Containing Aldehyde Oxidase from Coleoptiles of Maize

Abstract: Aldehyde oxidase (AO; EC 1231) that could oxidize indole-3-acetaldehyde into indole-3-acetic acid was purified approximately 2000-fold from coleoptiles of 3-d-old maize (Zea mays L) seedlings The apparent molecular mass of the native enzyme was about 300 kD as estimated by gel-filtration column chromatography Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the enzyme was composed of 150-kD subunits It contained flavin adenine dinucleotide, iron, and molybdenum as prosthetic groups and had absorption peaks in the visible region (300–600 nm) To our knowledge, this is the first demonstration of the presence of flavin adenine dinucleotide and metals in plant AO Other aromatic aldehydes such as indole-3-aldehyde and benzaldehyde also served as good substrates, but N-methylnicotinamide, a good substrate for animal AO, was not oxidized 2-Mercaptoethanol, p-chloromercu-ribenzoate, and iodoacetate partially inhibited the activity, but well-known inhibitors of animal AO, such as menadione and estradiol, caused no reduction in activity These results indicate that, although maize AO is similar to animal enzymes in molecular mass and cofactor components, it differs in substrate specificity and susceptibility to inhibitors Immunoblotting analysis with mouse polyclonal antibodies raised against the purified maize AO showed that the enzyme was relatively rich in the apical region of maize coleoptiles The possible role of this enzyme is discussed in relation to phytohormone biosynthesis in plants

The 2.0 Å crystal structure of catalase-peroxidase from Haloarcula marismortui

Abstract: Catalase-peroxidase is a member of the class I peroxidase superfamily. The enzyme exhibits both catalase and peroxidase activities to remove the harmful peroxide molecule from the living cell. The 2.0 A crystal structure of the catalase-peroxidase from Haloarcula marismortui (HmCP) reveals that the enzyme is a dimer of two identical subunits. Each subunit is composed of two structurally homologous domains with a topology similar to that of class I peroxidase. The active site of HmCP is in the N-terminal domain. Although the arrangement of the catalytic residues and the cofactor heme b in the active site is virtually identical to that of class I peroxidases, the heme moiety is buried inside the domain, similar to that in a typical catalase. In the vicinity of the active site, novel covalent bonds are formed among the side chains of three residues, including that of a tryptophan on the distal side of the heme. Together with the C-terminal domain, these covalent bonds fix two long loops on the surface of the enzyme that cover the substrate access channel to the active site. These features provide an explanation for the dual activities of this enzyme.

Catalase-like activity of horseradish peroxidase: relationship to enzyme inactivation by H2O2.

Abstract: H2O2 is the usual oxidizing substrate of horseradish peroxidase C (HRP-C). In the absence in the reaction medium of a one-electron donor substrate, H2O2 is able to act as both oxidizing and reducing substrate. However, under these conditions the enzyme also undergoes a progressive loss of activity. There are several pathways that maintain the activity of the enzyme by recovering the ferric form, one of which is the decomposition of H2O2 to molecular oxygen in a similar way to the action of catalase. This production of oxygen has been kinetically characterized with a Clark-type electrode coupled to an oxygraph. HRP-C exhibits a weak catalase-like activity, the initial reaction rate of which is hyperbolically dependent on the H2O2 concentration, with values for K(2) (affinity of the first intermediate, compound I, for H2O2) and k(3) (apparent rate constant controlling catalase activity) of 4.0 +/- 0.6 mM and 1.78 +/- 0.12 s(-1) respectively. Oxygen production by HRP-C is favoured at pH values greater than approx. 6.5; under similar conditions HRP-C is also much less sensitive to inactivation during incubations with H2O2. We therefore suggest that this pathway is a major protective mechanism of HRP-C against such inactivation.

Studies of the Esterase Activity and the Anion Inhibition of Bovine Zinc and Cobalt Carbonic Anhydrases

Abstract: 1 The rates of hydrolysis of nitrophenyl esters, catalyzed by bovine carbonic anhydrase, depend on the position of the nitro group and on the size of the acyl residue. The most rapidly hydrolyzed substrate of those investigated is p-nitrophenyl acetate. The catalyzed rates are proportional to both enzyme and ester concentrations. Only in the case of m-nitrophenyl acetate could a value of the Michaelis constant, Km, be estimated, approximately 10 mM. Product inhibition by o-nitrophenol occurs during the enzyme-catalyzed hydrolysis of o-nitrophenyl acetate. 2 The metal specificity of the enzyme seems to be independent of the substrate. Zn(II) and Co(II) are about equally effective in restoring esterase activity to the apoenzyme while all other metal ions studied do not activate or have a very small effect. 3 The pH-dependence of the esterase activity of both Zn(II)- and Co(II)-carbonic anhydrase is very similar to that of the CO2 hydration activity, and the basic form of a group with a pK near 7 is required for both reactions. Anionic inhibitors are strongly bound to the enzyme when this group is in its acidic form, but the inhibition is almost abolished at alkaline pH. 4 The inhibitory powers of cyanide and sulfide decrease at acid as well as at alkaline pH. The results agree with the assumption that, formally, CN− and HS− do not bind to the basic form of the enzyme, while HCN and H2S do not bind to the acidic form.