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Biomedical subjects

J B Ward

Publications and source records attributed to J B Ward.

108 records · Page 6Linked to original sources
PubMed1975

Effects of short term phosphorus deprivation on laying hens.

An experiment was conducted to determine the effects on laying hens of ingestion of a phosphorus deficient diet for 6, 9, or 21 days. Four experimental groups consisting of 3 replicates of 5 Leghorn pullets averaging 90 percent egg production were maintained in individual cages. A diet containing corn, soy, and meat and bone meal was formulated to contain 0.39 percent total P on a 90 percent dry matter basis (LP). A normal P diet (NP), 0.64 percent total P, was obtained by supplementation with an inorganic P source. Group 1 (Control) was fed the NP diet for 21 days. Groups 2, 3 and 4 were fed the LP diet for 6, 9, and 21 days respectively. Groups 2 and 3 resumed consumption of NP diet after 6 and 9 days. Individual egg production and egg weight were recorded daily. Individual hen determinations of serum P, g. shell/cm.2 surface area, and feed consumption by replicate were made at 3 or 4 day intervals. The serum P of Group 1 averaged 5.01 +/- 0.31 mg./100 ml. over the 21 days. Serum P was significantly reduced after 3 days of consuming the LP diet. Serum phosphorus of Groups 2,3, and 4 were 2.95 +/- 0.18, 3.03 +/- 0.24, 3.13 +/- 0.32 mg./100 ml. respectively after 6, 9, and 21 days of consuming the LP diet. Serum P returned to control levels within 4 days after resumption of the NP diet by Groups 2 and 3. There were no differences in feed consumption, egg production nor any detrimental effects on egg weight or shell calcification despite the low serum P. Body weight gain of the hens fed the phosphorus deficient diet for 21 days was significantly reduced. At the end of the experiment femur density was determined; the hens which had consumed the phosphorus deficient diet for 21 days had reduced femur density (osteoporous) compared to the control group or the hens fed the phosphorus deficient diet for only 9 days. It is concluded that pullets in 90 percent production can tolerate this low P diet for at least 9 days without apparent detrimental effects.

Animal Feed↗
PubMed1974

Peptidoglycan biosynthesis by preparations from Bacillus licheniformis: cross-linking of newly synthesized chains to preformed cell wall.

A wall-plus-membrane preparation from a Bacillus licheniformis mutant incorporated radioactivity from a peptidoglycan precursor in which the free amino group of diaminopimelic acid was blocked by (14)C-labelled acetyl group. This incorporation was penicillin-sensitive. The enzymically degraded product contained cross-linked dimers, showing that newly synthesized peptidoglycan chains had been cross-linked to the pre-existing cell wall.

Amino Acids, Diamino↗
PubMed1974

The synthesis of peptidoglycan in an autolysin-deficient mutant of Bacillus licheniformis N.C.T.C. 6346 and the effect of beta-lactam antibiotics, bacitracin and vancomycin.

The synthesis of peptidoglycan by cell-free membrane and membrane+wall preparations from an autolysin-deficient, beta-lactamase-negative mutant of Bacillus licheniformis N.C.T.C. 6346 was studied. The membrane preparation synthesized un-cross-linked polymer, the formation of which was not inhibited by beta-lactam antibiotics. Release of d-alanine by the action of d-alanine carboxypeptidase was inhibited variably according to the antibiotic. This inhibition was reversed by neutral hydroxylamine but not by the action of beta-lactamases or by washing. Bacitracin inhibited peptidoglycan synthesis, but not the d-alanine carboxypeptidase. Examination of peptidoglycan synthesized in the presence of excess of bacitracin showed that synthesis was not restricted to the addition of one disaccharide-pentapeptide unit at each synthetic site, an average of 2-3 disaccharide-pentapeptide units being added. Peptidoglycan synthesis was three- to four-fold more sensitive to vancomycin than was the release of d-alanine by the action of the carboxypeptidase. Incorporation of newly synthesized peptidoglycan into pre-existing cell wall was studied in membrane+wall preparations. This incorporation was catalysed by a benzylpenicillin- and cephaloridine-sensitive transpeptidase. The concentrations of these antibiotics giving 50% inhibition of incorporation were almost identical with those required to inhibit growth of the bacillus. Inhibition of the transpeptidase was reversed by treatment with beta-lactamase or by washing.

Alanine↗
PubMed1973

The chain length of the glycans in bacterial cell walls.

The glycan chain length of peptidoglycan was measured by reduction with NaB(3)H(4) and isolation of the resulting muramitol, indicative of the length of the chains as biosynthesized, and glucosaminol, which measured the length of the chains after rupture by endo-beta-N-acetylglucosaminidases. Measurement of the non-reducing terminal N-acetylglucosamine by Smith degradation confirmed the result.

Acetamides↗
PubMed1973

The direction of glycan synthesis in a bacterial peptidoglycan.

A cell-free membrane preparation from a poorly lytic mutant of Bacillus licheniformis was used to synthesize radioactive peptidoglycan. The product was apparently un-cross-linked. When UDP-N-acetyl[(14)C]glucosamine was used and the final peptidoglycan subjected to Smith degradation, no radioactive glycerol was found. On the other hand, when peptidoglycan labelled with meso-diamino[(14)C]pimelic acid was first hydrolysed in 0.1m-HCl at 60 degrees C for 2h and then subjected to alkaline conditions, radioactive lactyl-peptides were eliminated. The proportion of radioactive lactyl-peptide decreased with increasing time of incorporation. It is concluded that the glycan chains grow by extension at their reducing ends while remaining attached by some linkage labile to mild acid, such as a glycosyl link to undecaprenol pyrophosphate.

Amino Acids, Diamino↗
PubMed1973

Effect of phosphate limitation on the morphology and wall composition of Bacillus licheniformis and its phosphoglucomutase-deficient mutants.

Two very poorly lytic mutants of Bacillus licheniformis 6346 that had no teichuronic acid or glucose in their walls were phosphoglucomutase deficient. The walls of the mutants were less autolytic, and the lesion in the phosphoglucomutase gene and the formation of lytic amidase seemed to be interrelated. When phosphoglucomutase was regained or the effects of the deficiency were circumvented by the presence of galactose in the medium, the lytic enzyme was partially regained. When subjected to growth limitation by the supply of inorganic phosphate, the mutants ceased to make teichoic acid, and their walls contained a greatly increased proportion of mucopeptide. Under these conditions they formed irregular spheres which changed back to rods when inorganic phosphate was supplied. Both wall and protein synthesis were necessary for the changes in morphology. An intermediate crescent-shaped cell was formed in the change from sphere to a rod. The possible relationship of this morphological change to the distribution of biosynthetic sites is discussed.

Amidohydrolases↗
PubMed1973

Genetic studies of leucine biosynthesis in Bacillus subtilis.

The mutations in a series of leucine auxotrophs isolated after treatment with nitrosoguanidine, ultraviolet light, and ICR-191 have been mapped between ilvC and pheA on the Bacillus subtilis chromosome. A fine structure map of the region was constructed by transformation. Analysis of several strains by assaying levels of their leucine bioysnthetic enzymes has shown that the region encodes three enzymes. The order of the genes with respect to the biosynthetic steps catalyzed by the gene products is 1-3-2.

Bacillus subtilis↗
PubMed1973

Regulation of leucine biosynthesis in Bacillus subtilis.

The biosynthesis of alpha-isopropylmalate (alphaIPM) synthetase, IPM isomerase, and betaIPM dehydrogenase in Bacillus subtilis can be derepressed in leucine auxotrophs by limiting them for leucine. The derepression of the three enzymes is apparently coordinate. A class of mutants resistant to 4-azaleucine excretes leucine and has derepressed levels of all three enzymes. The azaleucine-resistance mutations may lie in a gene (azlA) encoding a repressor. Efforts to find mutations characteristic of a constitutive operator have been unsuccessful. No polar mutations have been found among nine leucine auxotrophs that have characteristics of frameshift mutations. The enzyme catalyzing the first step in leucine biosynthesis, alphaIPM synthetase, is sensitive to feedback inhibition by leucine. We conclude that leucine biosynthesis is controlled by the inhibition of the activity of the first biosynthetic enzyme by leucine, and by the repression of the synthesis of the first three biosynthetic enzymes by leucine. The repression of the three enzymes may be under the control of a single repressor and a single operator, or of a single repressor and a separate operator for each structural gene.

Alcohol Oxidoreductases↗
PubMed1972

N-acetylmuramyl-L-alanine amidase of Bacillus licheniformis and its L-form.

A cell wall lytic enzyme has been demonstrated to be a component of the membrane of Bacillus licheniformis NCTC 6346 and an l-form derived from it. The lytic enzyme, characterized as an N-acetylmuramyl-l-alanine amidase, is solubilized from membranes by nonionic detergents. Ionic detergents inactivate the enzyme. In the bacterium the specific activities of amidase and d-alanine carboxypeptidase in mesosomes are approximately 65% of those in membranes. Selective transfer of lytic enzyme from nongrowing L-forms, L-form membranes, and protoplasts to added walls occurred after mixing, and 31 to 77% of the enzyme lost from L-form membranes was recovered on the walls. Membranes isolated from L-forms growing in the presence of added walls contained as little as 13% of the amidase found in membranes of a control culture. These results have been interpreted as showing that in vivo the amidase is "bound" to the surface of the bacterial cell membrane in such a location that it can be readily accessible to the cell wall.

Alanine↗
PubMed1968

The purification and properties of two staphylolytic enzymes from Streptomyces griseus.

1. Two staphylolytic enzymes have been purified from cultures of a soil isolate of Streptomyces griseus. 2. The purified enzymes were shown to be basic proteins of low molecular weight. Each enzyme released N-acetylmuramic acid reducing groups from the cell walls of Staphylococcus aureus. 3. The enzymes lysed whole staphylococci best at higher pH values and lower ionic strengths than when the substrate was isolated cell walls or purified mucopeptide. 4. Added teichoic acid did not inhibit the enzymes, but it formed an ethanol-precipitable complex with them. 5. The possibility that teichoic acid on the surface of whole cells prevents the access of the enzymes to their mucopeptide substrate is discussed.

Bacterial Proteins↗
PubMed1968

The chemical composition of the membranes of protoplasts and L-forms of Staphylococcus aureus.

Membrane fractions were prepared from Staphylococcus aureus H and 100 after dissolution of the cell walls by a lytic enzyme from Streptomyces griseus. Membranes were also prepared from the L-forms derived from the same strains. The membranes were analysed for protein, lipid, carbohydrate and RNA contents, and the fatty acid composition of the lipids was determined. A branched-chain saturated C(15) acid was the major component in all samples, and the correspondence between L-forms and parent bacteria was fairly close. The lipids were separated into non-polar-lipid, glycolipid and phospholipid fractions; the L-forms contained a little more neutral lipid and much more glycolipid than the parent bacteria. In all membranes the glycolipid, which accounted for all the carbohydrate present, was a diglucosyl diglyceride. The major phospholipids of the protoplast membranes were phosphatidylglycerol and some lipoamino acids (lysine and a little alanine). On the other hand, diphosphatidylglycerol was the chief phospholipid found in L-form membranes.

Amino Acids↗
PubMedDate not supplied

Use of in vivo genetic toxicity data for risk assessment.

Mutagenicity studies have been used to identify specific agents as potential carcinogens or other human health hazards; however, they have been used minimally for risk assessment or in determining permissible levels of human exposure. The poor predictive value of in vitro mutagenesis tests for carcinogenic activity and a lack of mechanistic understanding of the roles of mutagens in the induction of specific cancers have made these tests unattractive for the purpose of risk assessment. However, the limited resources available for carcinogen testing and large number of chemicals which need to be evaluated necessitate the incorporation of more efficient methods into the evaluation process. In vivo genetic toxicity testing can be recommended for this purpose because in vivo assays incorporate the metabolic activation pathways that are relevant to humans. We propose the use of a multiple end-point in vivo comprehensive testing protocol (CTP) using rodents. Studies using sub-acute exposure to low levels of test agents by routes consistent with human exposure can be a useful adjunct to methods currently used to provide data for risk assessment. Evaluations can include metabolic and pharmacokinetic endpoints, in addition to genetic toxicity studies, in order to provide a comprehensive examination of the mechanism of toxicity of the agent. A parallelogram approach can be used to estimate effects in non-accessible human tissues by using data from accessible human tissues and analogous tissues in animals. A categorical risk assessment procedure can be used which would consider, in order of priority, genetic damage in man, genetic damage in animals that is highly relevant to disease outcome (mutation, chromosome damage), and data from animals that is of less certain relevance to disease. Action levels of environmental exposure would be determined based on the lowest observed effect levels or the highest observed no effect levels, using sub-acute low level exposure studies in rodents. As an example, the known genotoxic effects of benzene exposure at low levels in man and animals are discussed. The lowest observed genotoxic effects were observed at about 1-10 parts per million for man and 0.04-0.1 parts per million in subacute animal studies. If genetic toxicity is to achieve a prominent role in evaluating carcinogens and in characterizing germ-cell mutagens, minimal testing requirements must be established to ascertain the risks associated with environmental mutagen exposure. The use of the in vivo approach described here should provide the information needed to meet this goal.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗