PubMed Health⌕ Search

Biomedical subjects

R D Hancock

Publications and source records attributed to R D Hancock.

17 recordsLinked to original sources
PubMed2001

The use of micro-organisms for L-ascorbic acid production: current status and future perspectives.

L-Ascorbic acid (L-AA) has been industrially produced for around 60 years in a primarily chemical process utilising D-glucose (D-glc) as starting material. Current world production is estimated at approximately 80,000 tonnes per annum with a worldwide market in excess of U.S. $600 million. We present a brief overview of research geared to exploiting micro-organisms for the industrial production of vitamin C, with emphasis on recent approaches using genetically engineered bacterial strains. We also discuss the potential for direct production of L-AA exploiting novel biochemical pathways with particular reference to yeast fermentations. The potential advantages of these novel approaches over current chemical and biotechnological processes are outlined.

Ascorbic Acid↗
PubMed2001

Tuberization in potato involves a switch from apoplastic to symplastic phloem unloading.

Phloem unloading was studied in potato plants in real time during the early stages of tuberization using carboxyfluorescein (CF) as a phloem-mobile tracer, and the unloading pattern was compared with autoradiography of tubers that had transported (14)C assimilates. In stolons undergoing extension growth, apoplastic phloem unloading predominated. However, during the first visible signs of tuberization, a transition occurred from apoplastic to symplastic transport, and both CF and (14)C assimilates subsequently followed identical patterns of phloem unloading. It is suggested that the switch to symplastic sucrose unloading may be responsible for the upregulation of several genes involved in sucrose metabolism. A detailed analysis of sugar levels and (14)C sugar partitioning in tuberizing stolons revealed a distinct difference between the apical region of the tuber and the subapical region. Analysis of invertase activity in nontuberizing and tuberizing stolons revealed a marked decline in soluble invertase in the subapical region of swelling stolons, consistent with the switch from apoplastic to symplastic unloading. However, cell wall-bound invertase activity remained high in the apical 1 to 2 mm of tuberizing stolons. Histochemical analysis of potato lines transformed with the promoter of an apoplastic invertase gene (invGE) linked to a reporter gene also revealed discrete gene expression in the apical bud region. Evidence is presented that the apical and lateral tuber buds function as isolated domains with respect to sucrose unloading and metabolism.

Carbohydrate Metabolism↗
PubMed2000

Biosynthesis of L-ascorbic acid (vitamin C) by Saccharomyces cerevisiae.

Saccharomyces cerevisiae cells incubated with D-glucose (D-Glc), D-galactose or D-mannose (D-Man) synthesised D-erythroascorbic acid (D-EAA) but not L-ascorbic acid (L-AA). Accumulation of D-EAA was observed in cells incubated with D-arabinose (D-Ara) whilst accumulation of L-AA occurred in cells incubated with L-galactose (L-Gal), L-galactono-1,4-lactone and L-gulono-1,4-lactone. When S. cerevisiae cells were incubated with D-[U-(14)C]Glc, D-[U-(14)C]Man or L-[1-(14)C]Gal, incorporation of radioactivity into L-AA was observed only with L-[1-(14)C]Gal. Pre-incubation of yeast cells with D-Ara substantially reduced the incorporation of L-[1-(14)C]Gal into L-AA. Our results indicate that, under appropriate conditions, yeast cells can synthesise L-AA via the pathway naturally used for D-EAA biosynthesis.

Ascorbic Acid↗
PubMed1996

Indium (III) and gallium (III) complexes of bis(aminoethanethiol) ligands with different denticities: stabilities, molecular modeling, and in vivo behavior.

Complexes of Ga(III) and In(III) radionuclides are widely used in diagnostic imaging. In this study, the following ligands of denticities 4, 5, and 6 respectively were prepared: N,N'-bis-(2,2-dimethyl-2-mercaptoethyl) ethylenediamine (4SS), 1-carboxy-N-N'-bis(2,2-dimethyl-2- mercaptoethyl)ethylenediamine (5SS), and N,N'-bis(2,2- dimethyl-2-mercaptoethyl)ethylenediamine-N,N'-diacetic acid (6SS). Syntheses of the two new ligands, 5SS and 6SS, are described. Equilibrium constants for their In(III) and Ga(III) complexes were determined by both direct and ligand-competitive potentiometric methods. The formation constant (KML = [ML]/[M][L]) of In(III)--6SS in 0.100 M KNO3 at 25.0 degrees C is 10(39.8), and its pM at physiological pH (7.4 with 100% excess of the ligand) is 30.9. These values are higher than those of any other previous reported ligand for In(III). The stability constants of the complexes of 4SS, 5SS, 6SS, and the analogous ligand EDDASS, N,N'-bis(2-mercaptoethyl) ethylenediamine-N,N'-diacetic acid, which does not contain gem-dimethyl groups, are compared. The thermodynamic stabilities of the In(III) complexes of all ligands except 6SS are greater than those of the corresponding Ga(III) complexes. The presence of the geminal dimethyl groups in 6SS increased the stability of the Ga(III) and In(III) complexes over those of EDDASS. The effects of the gem-dimethyl groups on complex stabilities are explained by molecular modeling. The serum stabilities and biodistributions out to 1 h postinjection of 67/68Ga and 111In chelates of 4SS, 5SS, and 6SS were measured and compared with those of EDDASS. The 67/68Ga- and 111In-ligand complexes with more donor atoms showed were more stable in serum, both in vitro and in vivo. The biodistributions of the 67/68Ga- and 111In-ligand complexes exhibited distinct trends. None of the 67/68Ga- and 111In-chelates demonstrated significant heart or brain uptake. The majority of uptake for all compounds was in the liver and kidney. The degree of clearance through the liver corresponded to the thermodynamic stability of the complex. Correlations between in vivo behavior, molecular modeling data, and thermodynamic stability of the complexes are discussed.

Animals↗
PubMed1996

Perinatal mortality in lambs in southern Brazil.

Hypothermia and dystocia were found to be the most common causes of perinatal mortality in 8 commercial wool flocks in one region of southern Brazil. It was established that low birth weight and poor maternal instinct in the ewes predisposed to losses due to hypothermia but that there appeared to be no association with adverse weather conditions. Other factors possibly predisposing to losses are discussed.

Animals↗
PubMed1995

N,N'-ethylene-di-L-cysteine (EC) complexes of Ga(III) and In(III): molecular modeling, thermodynamic stability and in vivo studies.

There are several reports in the literature on the evaluation of chelates containing two nitrogens and two sulfurs (N2S2) as four coordinate ligands (in solution) for gallium and indium radiopharmaceuticals. No thermodynamic stability constants of these ligands were reported, and the stability of these complexes in vivo has been questioned. L,L-Ethylenedicysteine (EC) is a N2S2 ligand that also contains two carboxylic acid moieties for complexation of Ga(III) and In(III) in a hexacoordinate environment. The stability constants of Ga- and In-EC have been determined by potentiometric methods. The stability of In-EC was found to be greater than that of Ga-EC, with stability constants (log K's) of 33.0 and 31.5, respectively. A molecular mechanics evaluation of the Ga- and In-EC complexes support the thermodynamic results. 67Ga- and 111In-labeled complexes of EC were prepared and analyzed by thin layer chromatography and electrophoresis. Both complexes were evaluated in biodistribution studies in normal Sprague-Dawley rats. 111In-EC cleared rapidly through the hepatobiliary system, whereas 67Ga-EC remained in the liver at 1 h post-injection. Although 67Ga-EC was retained in the liver, suggesting instability of the complex in vivo. 67Ga-EC was stable in rat plasma in vivo at 2 h post-injection. Because of the high thermodynamic and in vivo stability of In-EC, derivatives of EC may have applications as bifunctional chelates for 111In-labeled proteins and peptides. More lipophilic analogues of 68Ga-EC may also have potential as myocardial PET imaging agents.

Animals↗
PubMed1993

Evaluation of a new chelating agent for cadmium: a preliminary report.

The Plasma Mobilizing Index parameters of the newly synthesized chelating agent THP-12-ane N4, determined by computer simulation studies, have indicated that this chelating agent might be a good antagonist for cadmium intoxication. Experiments conducted on rats confirmed this observation and showed that THP-12-ane N4 might have the ability to chelate and mobilize cadmium in vivo.

Animals↗
PubMed1992

Protection in simian immunodeficiency virus-vaccinated monkeys correlates with anti-HLA class I antibody response.

Our earlier reports demonstrated that Cynomolgus macaques vaccinated with either inactivated partially purified simian immunodeficiency virus (SIV), fixed SIV-infected C8166 (a human T lymphoblastoid cell line) cells, or fixed uninfected C8166 cells can be protected against a challenge infection with the 32H isolate of SIVmac 251 (grown in C8166) (Stott, E. J., W. L. Chan, K. H. G. Mills, M. Page, F. Taffs, M. Cranage, P. Greenway, and P. Kitchin. 1990. Lancet. 336:1538; Stott, E. J., P. A. Kitchin, M. Page, B. Flanagan, L. F. Taffs, W. L. Chan, K. H. G. Mills, P. Silvera, and A. Rodgers. 1991. Nature [Lond.]. 353:393). Protection is correlated with the levels of antibody response to cellular antigens in the human cells from which the virus immunogen was grown. However, the mechanism of protection is unclear. We report here the analysis of sera from these protected monkeys and demonstrate that there is positive correlation of protection with antibody response to the HLA class I molecule.

Animals↗
PubMed1991

Changes in psychotropic drug use in long-term residents of an ICF/MR facility.

Psychotropic drug use of 139 persons residing continuously over a 10-year period in an ICF/MR was monitored. Results indicate an ongoing decrease in psychotropic drug use, primarily antipsychotic agents, as well as the benefits of ongoing monitoring of individual drug usage. This monitoring can be utilized to minimize side effects of medication. Information obtained can be organized and utilized to improve care. Drug histories, when used with other data pertinent to targeted benefit to risk of medication.

Adult↗
PubMed1989

Bovine spongiform encephalopathy: diagnostic significance of vacuolar changes in selected nuclei of the medulla oblongata.

The adequacy of a histopathological diagnosis of bovine spongiform encephalopathy (BSE) based exclusively on observations of neuroparenchymal vacuolation in three specific neuroanatomic nuclei was tested by using a standard coronal section of medulla oblongata cut at the obex. The agreement between the observations and the definitive histopathological diagnosis was assessed in each of 684 bovine brains - 563 confirmed cases of BSE, 20 with changes which did not diagnose BSE conclusively and 101 in which the lesions of BSE were not detected. When the assessment was confined to the solitary tract nucleus and the spinal tract nucleus of the trigeminal nerve a positive result was obtained in 99.6 per cent of confirmed cases of BSE and only 1 per cent of brains in which lesions of BSE were not detected gave a false positive result. Thus an initial examination of the single section, together with an examination of representative areas of the rest of the brain when no unequivocal lesion was found, provided a satisfactory method for the routine diagnosis of BSE.

Animals↗
PubMed1988

Clinical observations on seasonal infertility in sows in Cornwall.

A summer infertility syndrome affected three commercial pig herds in Cornwall and was associated with reduced conception rates. The affected sows were housed in kennel and yard accommodation for all or part of gestation. The provision of more shelter accommodation for the dry sows in all three herds resulted in improved fertility. It is concluded that weather conditions between May and September may have adversely affected the fertility of these semi-extensive pig herds.

Animals↗