Search PubMed⌕ Search

Biomedical subjects

T Shiota

Publications and source records attributed to T Shiota.

At least 253 records · Page 14Linked to original sources
PubMed1978

A long-term study of the excretion of folate and pterins in a human subject after ingestion of 14C folic acid, with observations on the effect of diphenylhydantoin administration.

After the administration of 2-14C folic acid to a human volunteer, urinary and fecal radioactivity, as well as urinary excretion of folate (Lactobacillus casei assay) and biopterin-like material (Crithidia fasciculata assay) were determined at intervals over a 129 day period of observation. From two 24 h urine samples erythroneopterin, bioterin, threoneopterin pterin, isoxanthopterin, and xanthopterin were isolated by chromatographic procedures, quantitated, and their specific activities were determined. The effect on the pattern of elimination of urinary radioactivity and biological activity resulting from the administration of diphenylhydantoin was studied on two occasions. Urinary radioactivity plots suggest the decay of two forms of folates with markedly different biological half lives. One short-lived (t 1/2 approximately 31.5 hr), corresponding to newly absorbed folate, and one long-lived (t 1/2 approximately 100 day) thought to represent the decay of body pools. Diphenylhydantoin does not alter the rate of elimination of the long-lived component but may accelerate losses of newly absorbed folate. The analysis of pterins does not support the hypothesis that diphenylhydantoin increases the breakdown of folates to pterins.

Adult↗
PubMed1978

Virulence of Streptococcus mutans: comparison of the effects of a coupling sugar and sucrose on certain metabolic activities and cariogenicity.

A coupling sugar preparation (sucrose-free [CSSF]), which contains a mixture of sugars, oligosaccharides, and oligosaccharides terminated at the reducing end by sucrose, served as a substrate for growth and acid production by Streptococcus mutans 6715. However, CSSF was a poor substrate for cellular aggregation, glucosyltransferase activity, plaque formation, and adherence of cells to glass surfaces. In the presence of sucrose, CSSF inhibited glucosyltransfer activity and adherence of cells. The substitution of CSSF for sucrose in a rat diet significantly reduced caries score. Furthermore, rats fed diets containing sucrose and CSSF had significantly fewer carious lesions than did rats fed a sucrose diet.

Adhesiveness↗
PubMed1977

Partial purification of 6-(D-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydropterin triphosphate synthetase from chicken liver.

An enzyme that catalyzes the formation of 6-(D-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydropterin triphosphate (D-erythrodihydroneopterin triphosphate) and formic acid from GTP has been purified about 3700-fold from homogenates of chicken liver. The molecular weight of the enzyme, D-erythrodihydroneopterin triphosphate synthetase (GTP cyclohydrolase), has been estimated to be 125,000 by gel filtration on Ultrogel AcA-34. The enzyme functions optimally between pH 8.0 and 9.2 and is considerably heat-stable. No cofactors or metal ions have been demonstrated to be required for activity; however, the reaction is strongly inhibited by Cu2+ and Hg2+. GTP is the most efficient substrate, with GDP being 1/17 as active and guanosine, GMP, and ATP being inactive. The Km for GTP has been found to be 14 micrometer. Although the overall reaction catalyzed by D-erythrodihydroneopterin triphosphate synthetase from chicken liver is identical with that from Escherichia coli GTP cyclohydrolase, immunological studies show no apparent homology between the two enzymes.

Aminohydrolases↗
PubMed1977

Virulence of Streptococcus mutans: cariogenicity of S. mutans in adult gnotobiotic rats.

Gnotobiotic rats infected with Streptococcus mutant 6715, mutans C211 at 45 days of age on provided a purified diet containing 5% sucrose developed carious lesions on buccal, sulcal, and proximal molar surfaces within 15 days (60 days of age). The level of caries increased significantly (P less than or equal to 0.01) within the next 15 days (by day 75), an extensive decay was observed on all three molar surfaces of 90-day-old infected rats (45 days after challenge). Mutant C211 was previously shown to exhibit increased glucosyltransferase activity and greater adherence and virulence than S. mutans 6715 wild type (wt). Gnotobiotic rats (90 days of age) infected with either S. mutans AHT or S. mutans 6715 (wt) at 45 days of age developed significantly (P less than or equal to 0.01) fewer caries on all molar surfaces than rats of the same age that were infected with S. mutans 6715, mutant C211. The level of plaque increased 2-fold, and the number of viable S. mutans in plaque increased 10-fold between days 60 and 90 in rats infected with S. mutans 6715, mutant C211. Ninety-day-old rats infected with either S. mutans AHT or S. mutans 6715 (wt) had similar levels of plaque and numbers of S. mutans in plaque; however, these values were two- to fourfold lower than those observed in rats of the same age that were infected with S. mutans 6715, mutant C211.

Animals↗
PubMed1976

Enzymatic synthesis of biopterin from D-erythrodihydroneopterin triphosphate by extracts of kidneys from Syrian golden hamsters.

An enzyme system was found in either crude homogenates of dialyzed extracts of liver, kidney, lung, and brain from Syrian golden hamsters that catalyzed the synthesis of radioactive 6(L-erythro-1',2'-dihydroxypropyl)pterin (biopterin) from [U-14C]6(D-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydropterin triphosphate (D-erythrolH2neopterin-PPP) preparation. The specific radioactivity of biopterin was found to be comparable to that of D-erythroH2neopterin-PPP. The enzyme system from hamster kidney was purified severalfold by fractionation with ammonium sulfate and with an Ultrogel AcA-34 column. It was demonstrated that (a) NADPH or NADAH was essential and that (b) Mg2+ was stimulatory for the enzymatic synthesis of biopterin from D-erythroH2-NEOPTERIN-PPP. Also GTP and nonphosphorylated neopterins were not converted to biopterin. Although 6-lactyl-7,8-dihydropterin (sepiapterin) was converted to biopterin in the presence of NADPH, sepiapterin was not detected from D-erythroH2neopterin-PPP in the absence of NADPH. A preliminary experiment was performed to identify dihydrobiopterin.

Animals↗
PubMed1976

Isolation and characterization of dihydropteridine reductase from Pseudomonas species.

Dihydropteridine reductase isolated from the bacterium Pseudomonas species (ATCC 11299a) has been purified approximately 450-fold byammonium sulfate precipitation and diethylaminoethyl-cellulose chromatographic procedures. The preparation is at least 80% pure as judged by polyacrylamide gels. Its molecular weight was determined to be about 44,000. Both dihydropteridine reductase and phenylalanine hydroxylase activities were found to be higher in cells adapted to a medium containing L-phenylalanine or L-tyrosine as the sole carbon source than in those grown in L-asparagine. The substrate of the reductase is quinonoid dihydropteridine, and the product is tentatively identified as a tetrahydropteridine through its ability to serve as a cofactor for phenylalanine hydroxylase. The enzyme shows no marked specificity for the pteridine cofactor that occurs naturally in this organism, L-threo-neopterin. The pH optimum for the reductase is 7.2, and nicotinamide adenine dinucleotide, reduced form, is the preferred cosubstrate. Inhibition of the reduced and untreated enzyme by several sulfhydryl reagents was observed. A metal requirement for the reductase could not be demonstrated. Dihydropteridine reductase was found to be inhibited by aminopterin in a competitive manner with respect to the quinonoid dihydro form of 2-amino-4-hydroxy-6,7-dimethyl-5,6,7,8-tetrahydropteridine.

Aminopterin↗
PubMed1975

The nature of the multiple forms of D-erythrodihydroneopterin triphosphate synthetase.

1. Three forms of the Lactobacillus plantarum enzyme D-erythro-dihydroneopterin triphosphate synthetase, the first enzyme in folate biosynthesis, have been demonstrated by polyacrylamide gel electrophoresis. The enzyme forms designated the alpha prime, alpha and beta forms have been shown to be conformers with molecular weights of approx. 200 000. Study of the subunit structure of the beta enzyme species by sodium dodecylsulfate-polyacrylamide gel electrophoresis revealed a single protein with an estimated molecular weight of 20 000 which suggests that the enzyme molecule may be composed of ten polypeptide chains. 2. Of the three conformers only one form, the beta form, appears to be enzymatically active. The two other conformers must undergo conformational changes to the beta species before enzymatic activity can be demonstrated in reaction mixtures containing these enzyme forms. 3. The three enzyme species are interconvertible. The removal of phosphate ions from the enzymatically active beta form results in the formation of two inactive species which suggests that the conformation of the active enzyme is stabilized by non-covalently bound phosphate ions. Conversion of the inactive species to the beta enzyme form may be effected by the readdition of phosphate, substrate or certain nucleotides.

Aminohydrolases↗
PubMed1975

Virulence of Streptococcus mutans: biochemical and pathogenic characteristics of mutant isolates.

The in vitro dextran-sucrase activities and adherence to glass of S. mutans 6715 and PS14 wild types and mutants were quantitated and compared with their in vivo cariogenicity in young, gnotobiotic rats. In general, S. mutans PS14 mutants B414 and B421 and 6715 mutant C4 demonstrated less dextran-sucrase activity and adherence than parental strains and caused fewer carious lesions in gnotobiotic rats. Rats monoinfected with either PS14 mutants B414 or B421 had less plaque and viable S. mutans in plaque than rats infected with parental strain. Both S. mutans 6715 mutants C211 and C229, demonstrated greater enzyme activity and adherence than the parental strain and produced more carious lesions.

Adhesiveness↗