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.

HISTOCHEMICAL DEMONSTRATION OF β-d-GLUCURONIDASE WITH A SYNTHETIC SUBSTRATE

Abstract: The synthesis of a substrate, 6-bromo-2-naphthyl β-d-glucopyruronoside, is described, and the procedure for the histochemical demonstrations of β-d-glucuronidase activity and experiments to determi...

Purification and characterization of a biodegradable plastic-degrading enzyme from Aspergillus oryzae.

Abstract: We used biodegradable plastics as fermentation substrates for the filamentous fungus Aspergillus oryzae. This fungus could grow under culture conditions that contained emulsified poly-(butylene succinate) (PBS) and emulsified poly-(butylene succinate-co-adipate) (PBSA) as the sole carbon source, and could digest PBS and PBSA, as indicated by clearing of the culture supernatant. We purified the PBS-degrading enzyme from the culture supernatant, and its molecular mass was determined as 21.6 kDa. The enzyme was identified as cutinase based on internal amino acid sequences. Specific activities against PBS, PBSA and poly-(lactic acid) (PLA) were determined as 0.42 U/mg, 11 U/mg and 0.067 U/mg, respectively. To obtain a better understanding of how the enzyme recognizes and hydrolyzes PBS/PBSA, we investigated the environment of the catalytic pocket, which is divided into carboxylic acid and alcohol recognition sites. The affinities for different substrates depended on the carbon chain length of the carboxylic acid in the substrate. Competitive inhibition modes were exhibited by carboxylic acids and alcohols that consisted of C4-C6 and C3-C8 chain lengths, respectively. Determination of the affinities for different chemicals indicated that the most preferred substrate for the enzyme would consist of butyric acid and n-hexanol.

Substrate Atomic-Termination-Induced Anisotropic Growth of ZnO Nanowires/Nanorods by the VLS Process

Abstract: In the vapor-liquid-solid (VLS) growth of 1D nanostructures, the electronic structure of the substrate surface may critically affect the morphology of the grown nanowires/nanorods. In this paper, using a model system of the Sn-catalyzed growth of ZnO nanostructures on a single-crystal ZnO substrate, we demonstrate the effect of substrate surface termination on nanowire growth. Symmetric nanoribbons have been grown on the nonpolar surfaces of ((21 h10) (or ((011 h0)), but the polar surface ((0001) substrates have asymmetrically grown nanostructures. For the Zn-terminated (0001) substrate surface, uniform, long, and epitaxially aligned nanowires have been grown. For the oxygen-terminated (0001 h) substrate surface, short nanotrunks have been grown. These asymmetrical growth features are related to the atomic termination of the substrate, surface charges, and interface adhesion. These observations provide some insight into the physical chemical process in VLS growth.

Purification and characterization of adenosine triphosphate: ribonucleic acid adenyltransferase from Escherichia coli.

Abstract: A primer-dependent poly (A)-polymerizing activity using ATP as substrate (ATP: RNA adenyltransferase) was isolated in high yield from Escherichia coli and purified to apparent homogeneity. For this purpose an assay system had to be used which restricted a variety of infering enzyme activities. Since the enzyme aggregates to macromolecular cell components or precipitates when kept in low salt conditions (<0.4 M NaCl), it was necessary to perform the entire purification procedure in high salt conditions. This was accomplished by using a high salt ribosomal supernatant, a polyethylenglycol-dextran-NaCl phase partition step and a very efficient final high salt phosphocellulose chromatography. At 0.5 M NaCl the enzyme has a molecular weight of approximately 58000. Dodecylsulfate gel electrophoresis shows a single polypeptide chain of molecular weight × 50000. The enzyme has a high preference for ATP as substrate. Manganese ions show higher activity as cofactors than magnesium ions. All classes of natural RNAs are used as primers. The free 3′terminal hydroxyl group of the RNA is required. The enzyme is unable to catalyze a pyrophosphorolysis or a phosphorolysis reaction. It is shown that ATP: RNA adenyl-transferase preferentially synthesizes rather long chains of poly(A) attached to the RNA primers. No relation between the enzyme protein and subunits of the DNA-dependent RNA polymerase could be detected.

p-Hydroxyphenylacetate decarboxylase from Clostridium difficile. A novel glycyl radical enzyme catalysing the formation of p-cresol.

Abstract: The human pathogenic bacterium Clostridium difficile is a versatile organism concerning its ability to ferment amino acids. The formation of p-cresol as the main fermentation product of tyrosine by C. difficile is unique among clostridial species. The enzyme responsible for p-cresol formation is p-hydroxyphenylacetate decarboxylase. The enzyme was purified from C. difficile strain DMSZ 1296T and initially characterized. The N-terminal amino-acid sequence was 100% identical to an open reading frame in the unfinished genome of C. difficile strain 630. The ORF encoded a protein of the same size as the purified decarboxylase and was very similar to pyruvate formate-lyase-like proteins from Escherichia coli and Archaeoglobus fulgidus. The enzyme decarboxylated p-hydroxyphenylacetate (Km = 2.8 mm) and 3,4-dihydroxyphenylacetate (Km = 0.5 mm). It was competitively inhibited by the substrate analogues p-hydroxyphenylacetylamide and p-hydroxymandelate with Ki values of 0.7 mm and 0.48 mm, respectively. The protein was readily and irreversibly inactivated by molecular oxygen. Although the purified enzyme was active in the presence of sodium sulfide, there are some indications for an as yet unidentified low molecular mass cofactor that is required for catalytic activity in vivo. Based on the identification of p-hydroxyphenylacetate decarboxylase as a novel glycyl radical enzyme and the substrate specificity of the enzyme, a catalytic mechanism involving ketyl radicals as intermediates is proposed.