PubMed · 9590046
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
T Ohura. 1998. [Propionic acidemia].. https://pubmed.ncbi.nlm.nih.gov/9590046/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
A microsomal preparation from seedlings of Zea mays catalyzed the NAD+-dependent oxidative decarboxylation of several substrates, including 4alpha-carboxy-cholest-7-en-3beta-ol, synthesized according to a new procedure, giving the first in vitro evidence for this enzymatic activity in a higher plant. A GC assay has been developed to detect the Delta7-cholestenone produced and the kinetic parameters of the microsomal system have been established. 4alpha-Carboxysterol decarboxylation shows an exclusive requirement for an oxidized pyridine nucleotide, with NAD+ being more efficient than NADP+. The decarboxylation reaction is independent of molecular oxygen. 4alpha-Carboxysterol-C3-dehydrogenase/C4-decarboxylase (4alpha-CD) is a microsome-bound protein which can be efficiently solubilized by detergents, including Brij W-1 and sodium cholate. The Brij W-1-solubilized enzyme was partially purified 290-fold by a combination of DEAE anion-exchange chromatography, Cibacron blue 3GA-agarose dye chromatography, and gel permeation. The apparent molecular mass of 4alpha-CD in sodium cholate was estimated to be 45 kDa. These results support the contention that demethylation at C4 of plant sterols is composed of two separate processes: an oxygen- and NAD(P)H-dependent oxidation of the 4alpha-methyl group to produce the 4alpha-carboxysterol metabolite (S. Pascal et al., J. Biol. Chem. 268, 11639, 1993) followed by oxygen-independent dehydrogenation/decarboxylation to produce an obligatory 3-ketosteroid.
The DNA fragment encoding malonate decarboxylase, involved in malonate assimilation, was cloned from Pseudomonas putida. The 11-kb DNA fragment contained nine open reading frames, which were designated mdcABCDEGHLM in the given order. N-terminal protein sequencing established that the mdcA, mdcC, mdcD, mdcE and mdcH genes encoded subunits alpha, delta, beta, gamma and epsilon of the malonate decarboxylase, respectively. Malonate decarboxylase was functionally expressed in Escherichia coli from plasmid harboring the entire gene cluster or the mdc genes lacking the mdcL and mdcM genes. The mdcL and mdcM genes encode membrane proteins and disruption of the genes of P. putida by the insertion of a kanamycin resistance cassette reduced the malonate uptake activity of the organism. Thus, we conclude that MdcLM is a malonate transporter.
Epoxide carboxylase from the bacterium Xanthobacter strain Py2 is a multicomponent enzyme system which catalyzes the pyridine nucleotide-dependent carboxylation of aliphatic epoxides to beta-ketoacids as illustrated by the reaction epoxypropane + CO2 + NADPH + NAD+ --> acetoacetate + H+ + NADP+ + NADH. The combination of four distinct proteins, designated components I-IV, are required for the reconstitution of epoxide carboxylase activity with racemic mixtures of short-chain (C3-C5) terminal epoxyalkanes. In this work, components III and IV of the epoxide carboxylase system are shown to confer specificity for epoxyalkane enantiomers. Components I-III supported the carboxylation of (R)-epoxypropane, while components I, II, and IV supported the carboxylation of (S)-epoxypropane. At fixed concentrations of components I and II, the rates of (R)- and (S)-epoxypropane carboxylation saturated with increasing concentrations of component III or IV to give identical maximal rates for the two epoxide substrates. (S)-Epoxypropane was an inactivator of (R)-epoxypropane carboxylation by components I- III, while (R)-epoxypropane was an inactivator of (S)-epoxypropane carboxylation by components I, II, and IV. These inactivating effects were fully reversed upon the addition of the correct complementing dehydrogenase component. Amino acid sequence analysis of components III and IV demonstrates that they belong to the short-chain dehydrogenase/reductase (SDR) family of enzymes. Both components contain highly conserved residues within the coenzyme binding fold and catalytic regions found in SDR enzymes. Components III and IV are proposed to catalyze the NAD+-dependent abstraction of a hydride from a chiral secondary alcohol-like intermediate bound to the active site component of the enzyme system to form the corresponding beta-ketone intermediate. A multicomponent epoxide carboxylase system was purified to homogeneity from Nocardia corallina B276, a bacterium phylogenetically unrelated to Xanthobacter Py2, and found to consist of four proteins with functions identical to those of the Xanthobacter Py2 system. The stereoselective dehydrogenases of the Xanthobacter epoxide carboxylase system were able to substitute for the corresponding components of the N. corallina system when using (R)- and (S)-epoxypropane as substrates, and vice versa. These results provide the first demonstration of the involvement of stereospecific dehydrogenases in aliphatic epoxide metabolism and provide new insights into microbial strategies for the utilization of chiral organic molecules.