Search PubMed⌕ Search

Biomedical subjects

D W Rice

Publications and source records attributed to D W Rice.

139 records · Page 8Linked to original sources
PubMed1984

Structural relationship between glutathione reductase and lipoamide dehydrogenase.

The elucidation of the primary structure of the Escherichia coli lipoamide dehydrogenase (EC 1.8.1.4) by sequencing the corresponding structural gene (lpd) has enabled a detailed structural comparison between lipoamide dehydrogenase and the related disulphide oxido-reductase, human erythrocyte glutathione reductase (EC 1.6.4.2). Some 28% of the amino acid residues were found to be identical and a striking degree of homology was apparent throughout the polypeptide chains. It was concluded that the two enzymes possess very similar three-dimensional structures with particularly strong conservation of residues around the FAD and NAD(P) binding sites and at the redox centres of the molecules. Significant amino acid substitutions occur in the substrate binding pocket and these include an extra 18 amino acid residues at the C terminus of lipoamide dehydrogenase. Under physiological conditions, lipoamide dehydrogenase and glutathione reductase act in opposite directions, passing reducing equivalents to NAD+ or from NADPH (respectively), and two key substitutions near the redox centre could be associated with this difference in function. This study represents the first direct structural comparison between two related enzymes that are NADP+-linked (glutathione reductase) and NAD+-linked (lipoamide dehydrogenase). The differential recognition of these two cofactors could be explained in terms of amino acid substitutions. A divergent evolutionary relationship between the two enzymes including their NAD and NADP binding domains is fully supported by this analysis.

Amino Acid Sequence↗
PubMed1984

Ferritin: design and formation of an iron-storage molecule.

Although essential for most forms of life, too much iron is harmful. To cope with these antagonistic phenomena an iron-storage molecule, ferritin, has evolved. The structure of horse spleen apoferritin, which has recently been refined, consists of 24 symmetrically related subunits forming a near-spherical hollow shell. In ferritin the central cavity is occupied by an iron core of 'ferrihydrite', a geologically ephemeral mineral found in hot or cold springs and in mine workings, or produced in the laboratory by heating solutions of ferric salts. Ferritin itself forms most readily from apoferritin, in the presence of dioxygen, from FeII, not FeIII. Access to its interior is through small intersubunit channels, and the protein influences both the rate of FeII-oxidation and the form of oxide produced.

Animals↗
PubMed1983

Homology between CAP and Fnr, a regulator of anaerobic respiration in Escherichia coli.

The fnr gene is essential for the expression of anaerobic respiratory metabolism in Escherichia coli. Genetic and biochemical studies support the view that its product. Fnr, is a transcriptional regulatory protein specific for genes encoding anaerobic respiratory functions (fumarate, nitrate and nitrite reductases, hydrogenase, etc.). In this respect Fnr may be considered analogous to the well-characterized catabolite gene activator protein (CAP), which mediates the control of catabolite-sensitive gene transcription. With a view to identifying its function, the fnr gene has recently been cloned and the primary structure of the Fnr protein deduced from the nucleotide sequence. This has revealed the presence of three regions of sequence homology with CAP. One corresponds to the DNA-binding site, a region of about 20 highly conserved amino acids that is believed to form a characteristic three-dimensional structure in several transcriptional regulators. The other regions of homology are in the nucleotide binding domain of CAP but the residues that interact with cAMP are not identical in Fnr. These homologies suggest that Fnr and CAP may have similar three-dimensional structures and that the regulation of anaerobic energy metabolism may involve interaction between Fnr and an unidentified effector molecule.

Amino Acids↗
PubMed1982

The comparative metabolism and toxic potency of aflatoxin B1 and aflatoxin M1 in primary cultures of adult-rat hepatocytes.

Both aflatoxin B1 (AFB1) and a hydroxylated metabolite, aflatoxin M1 (AFM1), were potent cytotoxins and genotoxins to primary cultures of rat hepatocytes. However, AFB1 stimulated the release of lactate dehydrogenase into the culture medium and the loss of viable cells from the monolayer at lower doses than did AFM1. The lowest toxic doses of AFB1 and AFM1 were 0.05-01 and 0.6 microgram/culture, respectively. Genotoxicity, determined by an assay for stimulation of DNA repair, was apparent at lower doses than was cytotoxicity. AFB1 was again more potent than AFM1, stimulating DNA repair at 0.025 microgram/culture, compared to the lowest genotoxic dose of AFM1 of 0.05 microgram/culture. At higher doses (1.2-2.4 microgram/culture) the responses due to both aflatoxins in the cytotoxicity and DNA-repair assays were approximately equal. The metabolism of a low dose (c. 0.17 microgram/culture) of [14C]AFB1 and [3H]AFM1 by cultured hepatocytes differed significantly. After 1 hr, 50% of the [14C]AFB1 remained unchanged in the culture medium, whereas about 18 hr were required for the same amount of [3H]AFM1 metabolism to occur [14C]AFB1 was metabolized to AFM1, to polar metabolites recovered in the aqueous phase after chloroform extraction, and to metabolites covalently bound to hepatocyte macromolecules. [3H]AFM1 was also metabolized to polar metabolites and to forms bound to macromolecules. The degree of covalent binding of the aflatoxins correlated with their cytotoxicity and genotoxicity at lower doses. After a 24-hr incubation, 12.5% of the dose of [14C]AFB1 was covalently bound to macromolecules compared to 1.5% of [3H]AFM1. Although AFM1 was less potent than AFB1 in cytotoxicity, DNA-repair and covalent-binding assays using primary cultures of hepatocytes, AFM1 was still active at relatively low doses and therefore is probably a potent hepatotoxin in vivo.

Aflatoxin B1↗
PubMed1982

Aflatoxin M1: in vitro preparation and comparative in vitro metabolism versus aflatoxin B1 in the rat and mouse.

A rapid, simple and relatively inexpensive biotransformation method using microsomes from 3-methylcholanthrene (3MCA) pretreated rats is described for the production of aflatoxin M1 (AFM1) is sufficient quantities for metabolism studies. A comparison is made of the metabolism of AFM1 and AFB1 by the postmitochondrial (S-10) fraction from mouse and rat hepatocytes. AFM1, in both species, is metabolized more slowly than AFB1, with its major metabolites being found in the aqueous fraction and very little associated with S-10 protein. In contrast, AFB1 is metabolized to numerous chloroform-extractable, protein bound and water-soluble metabolites. The toxicological implications of reduced protein binding and slower metabolism for AFM1 are discussed.

Aflatoxin B1↗
PubMed1981

Phosphoglycerate kinase.

Phosphoglycerate kinase catalyses the high-energy phosphoryl transfer of the acyl phosphate of 1,3-bisphosphoglycerate to ADP to produce ATP, a reaction requiring magnesium ions. The enzyme is widely distributed and apparently highly conserved as a monomer of molecular mass 45 000. X-ray studies of the enzymes from horse muscle and yeast, carried out in Oxford and Bristol respectively, have shown that the molecular structures of the two enzymes are almost identical. The most striking aspect of the structure is that the single polypeptide chain is organized into two separated domains composed of the N-terminal and C-terminal halves of the chain. Substrate binding studies and the determination of the complete amino acid sequence of the horse enzyme suggest that the nucleotide substrates and the phosphoglycerate substrates are bound to the C-domain and N-domain, respectively, in sites that are separated by about 12 A. In order to bring the two substrates together for catalysis, a hinge-bending conformational change involving helix rotation has been proposed, for which there is independent evidence from solution studies. Crystals of the ternary complex of the horse enzyme have been prepared that may contain the folded form of the enzyme.

Amino Acid Sequence↗
PubMed1979

Sequence, structure and activity of phosphoglycerate kinase: a possible hinge-bending enzyme.

The fitting of sequenced peptides to a high-resolution X-ray map of phosphoglycerate kinase has yielded the complete sequence and structure of the horse muscle enzyme. Metal ADP and ATP substrates are bound to one of the two widely separated domains in an environment that seems unsuitable for phosphoglycerate binding. The most plausible binding site for the phosphoglycerate substrate is on the other domain about 10 A from the ATP, which implies the possibility of a large scale hinge-bending of the domains to bring the two substrates together in a water-free environment for catalysis.

Amino Acid Sequence↗
PubMedDate not supplied

Development of California Public Health Goals (PHGs) for chemicals in drinking water.

As part of a program for evaluation of environmental contaminants in drinking water, risk assessments are being conducted to develop Public Health Goals (PHGs) for chemicals in drinking water, based solely on public health considerations. California's Safe Drinking Water Act of 1996 mandated the development of PHGs for over 80 chemicals by 31 December 1999. The law allowed these levels to be set higher or lower than federal maximum contaminant levels (MCLs), including a level of zero if data are insufficient to determine a specific level. The estimated safe levels and toxicological rationale for the first 26 of these chemicals are described here. The chemicals include alachlor, antimony, benzo[a]pyrene, chlordane, copper, cyanide, dalapon, 1,2-dichlorobenzene, 1,4-dichlorobenzene, 2,4-D, diethylhexylphthalate, dinoseb, endothall, ethylbenzene, fluoride, glyphosate, lead, nitrate, nitrite, oxamyl, pentachlorophenol, picloram, trichlorofluoromethane, trichlorotrifluoroethane, uranium and xylene(s). These risk assessments are to be considered by the State of California in revising and developing state MCLs for chemicals in drinking water (which must not exceed federal MCLs). The estimates are also notable for incorporation or consideration of newer guidelines and principles for risk assessment extrapolations.

Algorithms↗
PubMedDate not supplied

Similarity searching in databases of three-dimensional molecules and macromolecules.

This paper discusses algorithmic techniques for measuring the degree of similarity between pairs of three-dimensional (3-D) chemical molecules represented by interatomic distance matrices. A comparison of four methods for the calculation of 3-D structural similarity suggests that the most effective one is a procedure that identifies pairs of atoms, one from each of the molecules that are being compared, that lie at the center of geometrically-related volumes of 3-D space. This atom mapping method enables the calculation of a wide range of types of intermolecular similarity coefficient, including measures that are based on physicochemical data. Massively-parallel implementations of the method are discussed, using the AMT Distributed Array Processor, that achieve a substantial increase in performance when compared with a sequential implementation on a UNIX workstation. Current work involves the use of angular information and the extension of the method to field-based similarity searching. Similarity searching in 3-D macromolecules is effected by the use of a maximal common subgraph (MCS) isomorphism algorithm with a novel, graph-based representation of the tertiary structures of proteins. This algorithm is being used to identify similarities between the 3-D structures of proteins in the Brookhaven Protein Data Bank; its use is exemplified by searches involving the NAD-binding fold motif.

Algorithms↗
PubMedDate not supplied

Histologic lesions associated with intravenous infusions of large volumes of isotonic saline solution in rats for 30 days.

The objective of this study was to characterize the changes associated with intravenous infusions of large volumes of isotonic saline solution in rats so that effects of the infusion process could be more easily distinguished from effects of test articles. Male Sprague-Dawley rats weighing approximately 225-275 g at the beginning of the study were given intravenous infusions of isotonic saline solution once daily for 30 consecutive days at dosages of 40 or 80 ml/kg body weight. Saline solution was administered through catheters placed in the caudal veins of the tail according to one of the following regimens: 80 ml/kg at 0.25 ml/min; 80 ml/kg at 0.5 ml/min; 80 ml/kg at 1.0 ml/min; and 40 ml/kg at 1.0 ml/min. Control rats were catheterized but not administered intravenous fluids. One day following the last treatment, all rats were necropsied and major organs were collected in 10% formalin. Histologic lesions associated with treatment included increased incidence and severity of pulmonary periarterial infiltrates of eosinophils, multifocal pulmonary inflammation, pulmonary granulomas that often contained hairshaft fragments, endothelial hypertrophy and hyperplasia within pulmonary arterial vessels, and pulmonary arterial medial thickening. Infiltrates of eosinophils around small pulmonary arteries were more severe in rats given intravenous infusions than in untreated rats and were more severe in rats given isotonic saline at the 80-ml/kg dosage than at the 40-ml/kg dosage. The severity of periarterial infiltrates of eosinophils increased with increasing infusion rates in rats that received 80 ml/kg isotonic saline. Pulmonary granulomas and multifocal pulmonary inflammation were observed in more rats that received intravenous saline than in control rats, but their incidences did not appear to vary with the volume or rate of infusion. Multifocal endothelial hypertrophy and hyperplasia occurred in most rats given isotonic saline solution at all volumes and rates, but not in untreated control rats. Inflammatory lesions in the tail near the injection site were considered sequellae of catheter insertion that, in some instances, may have been exacerbated by intravenous saline infusion. There were no lesions in other organs that were attributable to intravenous infusions of isotonic saline solution.

Animals↗
PubMedDate not supplied

Production and isolation of aflatoxin M1 for toxicological studies.

One hundred mg aflatoxin M1 was produced and purified for toxicological studies. Aspergillus flavus NRRL 3251 was cultured on rice to produce aflatoxins B1, B2, M1, and M2, B1 and B2 were separated from M1 and M2 by a normal phase low pressure liquid chromatography (LC) column. M1 was then separated from M2 by a reverse phase low pressure LC column. Recoveries of aflatoxins from the LC columns were about 90%. The purified M1 was confirmed by ultraviolet-visible spectrometry, mass spectrometry, nuclear magnetic resonance spectrometry, optical rotation, and its mutagenicity to Salmonella typhimurium TA98.

Aflatoxin M1↗