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.

Inhibition of human mitochondrial aldehyde dehydrogenase by 4-hydroxynon-2-enal and 4-oxonon-2-enal.

Abstract: Previous studies found the lipid peroxidation product 4-hydroxynon-2-enal (4HNE) to be both a substrate and an inhibitor of mitochondrial aldehyde dehydrogenase (ALDH2). Inhibition of the enzyme by 4HNE was demonstrated kinetically to be reversible at low micromolar aldehyde but may involve covalent modification at higher concentrations. Structurally analogous to 4HNE is the lipid peroxidation product 4-oxonon-2-enal (4ONE), which is more reactive than 4HNE toward protein nucleophiles. The goal of this work was to determine whether 4ONE is a substrate or inhibitor of human ALDH2 (hALDH2) and elucidate the mechanism of enzyme inhibition by 4HNE and 4ONE. Both 4ONE and its glutathione conjugate were found to be substrates for the enzyme in the presence of NAD. At low concentrations of 4ONE (< or = 10 microM), hALDH2 catalyzed the oxidation of 4ONE to 4-oxonon-2-enoic acid (4ONEA) with a maximal yield of 5.2 mol 4ONEA produced per mol of enzyme (monomer). However, subsequent analysis of hALDH2 activity toward propionaldehyde revealed that both 4ONE and the oxidation product, 4ONEA, were potent, irreversible inhibitors of the enzyme. In contrast, inhibition of hALDH2 by a high concentration of 4HNE (i.e., 50 microM) was primarily reversible. The reactivity of 4ONEA toward glutathione was measured and found to be comparable to that of 4HNE, indicating that the 4ONE-oxidation product is a reactive electrophile. hALDH2/NAD was incubated with 4HNE, 4ONE, and 4ONEA, and mass spectral analysis of tryptic peptides revealed covalent modification of an hALDH2 active site peptide by both 4ONE and 4ONEA. These data demonstrate that hALDH2 catalyzes the oxidation of 4ONE to 4ONEA; however, the product 4ONEA is a reactive electrophile. Furthermore, both 4ONE and 4ONEA are potent, irreversible inhibitors of the enzyme.

Substrate water interactions within the Photosystem II oxygen evolving complex

Abstract: The 18O exchange rates for the substrate water in photosystem II can be obtained by time-resolved mass spectrometric approaches and provide insight into the chemical nature of the substrate binding sites in the oxygen evolving complex (OEC). In this communication, we report additional data on the resolvable S-state dependence of the substrate exchange rates in untreated spinach thylakoids. The data reveals that the exchange for one substrate water molecule is resolvable in all S states, i.e. S0 (k1 ≈ 10 s−1), S1 (k1 ≈ 0.02 s−1), S2 (k1 ≈ 2.0 s−1) and S3 (k1 ≈ 2.0 s−1), and that the second substrate water molecule is resolvable in S2 (k2 ≈ 120 s−1) and S3 (k2 ≈ 40 s−1) states, and faster than 120 s−1 during the S0 and S1 states. The temperature dependencies of the exchange rates are also reported. The corresponding activation energies for the slow exchange substrate water in S1, S2 and S3 are 83 ± 4, 71 ± 9, and 78 ± 9 kJ mol−1, respectively. In contrast, the activation energy for the fast exchange substrate water in S3, is 40 ± 5 kJ mol−1. Finally we also report the secondary isotope effect of deuterium on S3 state measurements, where the slow exchange substrate water remains unaffected while the rate for the fast exchange substrate water increases by a factor of ∼35%, resulting in an inverse H/D isotope effect. The exchange rates, activation energies and deuterium effects provide further mechanistic constraints on the water oxidation reaction in photosystem II and provide strong evidence that the slow exchange substrate water does not undergo any significant changes in its binding properties during the S2–S3 transition.

Method for manufacturing thin film

Abstract: A method for manufacturing a thin film includes the steps of loading a substrate into a reaction chamber, and terminating the surface of the substrate loaded into the reaction chamber by a specific atom. A first reactant is chemically adsorbed on the terminated substrate by injecting the first reactant into the reaction chamber including the terminated substrate. After removing the first reactant physically adsorbed into the terminated substrate, a solid thin film is formed through chemical exchange or reaction of the chemically adsorbed first reactant and a second reactant by injecting the second reactant into the reaction chamber. According to the thin film manufacturing method according to the present invention, it is possible to grow a thin film on the substrate in a state in which the no or little impurities and physical defects are generated in the thin film and interface of the thin film.

Kinetics of the reaction of renin with nine synthetic peptide substrates

Abstract: A number of peptides have been synthesized which represent portions of the tetradecapeptide renin substrate molecule, and which contain the hydrolyzable leu-leu bond. An automatic chemical method for determination of the velocity of the reaction of renin with these compounds was developed. Application of the method at several levels of substrate concentration permitted construction of Lineweaver-Burk plots, and calculation of Michaelis constants (Km) and maximal velocities (Vmax). The results show that the maximum affinity of the enzyme (lowest Km) for substrate is achieved only with the full tetradecapeptide molecule (asp1-arg2-val3-tyr4-ileu5-his6-pro7-phe8-his9-leu10-leu11-val12-tyr13-ser14). Removal of asp1 and arg2 from the N-terminal increases the Km eight-fold. Further, moderate increase in Km occurs when the next amino acids, val3, tyr4 and ileu5, are removed. The further removal of his6 results in a marked reduction in the Vmax. Removal of ser14 from the C-terminal of the nonapeptide his6-pro7-phe8-his9-leu10-leu11-val12-tyr13-ser14 does not greatly affect the Km nor the Vmax. Further removal of tyr13 from this compound results in complete loss of substrate activity. It is suggested that the compounds his6-pro7-phe8-his9-leu10-leu11-val12-tyr13-ser14 or his6-pro7-phe8-his9-leu10-leu11-val12-tyr13 might be used as substrates for the chemical assay and standardization of renin.

Magnetic recording medium.

Abstract: Magnetic recording medium comprising a non-magnetic substrate having formed thereon a magnetic layer. The magnetic layer comprises 1 to 8 wt % of one or more of metals selected for among B, Al, Si, P, Ge, Sn, Sb, Se, Te, Pb, Bi, Cu, Ti, V, Cr, Zr, Nb, Mo, W, and Ta, up to 13 wt % of one or more of rare earth elements selected from among Y, La, Ce, Pr, Nd, Sm, Gd, Tb, and Dy, 3 to 13 wt % of oxygen, and the balance of Co and unavoidable impurities. This magnetic layer may contain up to 22 wt % of Ni. This magnetic recording medium is excellent in both corrosion resistance and magnetic properties.