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D Lloyd

Publications and source records attributed to D Lloyd.

At least 91 records · Page 5Linked to original sources
PubMed1999

Kinetics, stereospecificity, and expression of the malolactic enzyme.

Mass spectrometric measurement of carbon dioxide production was used to study malolactic fermentation (MLF) in Lactobacillus collinoides isolated from cider. The kinetics and stereospecificity of the malolactic enzyme (MLE) were studied, and the stoichiometry of the reaction sequence was investigated. The optimum pH for activity of the MLE was 4.9. MLF was more rapid (in both intact cells and cell extracts) when L-malic acid was used than when D-malic acid or the racemic mixture was added. The enzyme was found to be constitutively present in L. collinoides. Addition of L-malic acid (37 mM) to the growth medium resulted in increased MLE activity; addition of the D isomer alone or the racemic mixture resulted in lower activities. Addition of the main sugars in apple juice (fructose, sucrose, and glucose) to the growth medium in the presence of malic acid repressed production of MLE to similar extents in all three cases; in the absence of malic acid, instead of inhibiting MLF, addition of sugars to the growth medium somewhat increased the residual MLE activity.

Beverages↗
PubMed1998

NO+, but not NO., inhibits respiratory oscillations in ethanol-grown chemostat cultures of Saccharomyces cerevisiae.

A continuous culture of Saccharomyces cerevisiae strain IFO 0233 growing aerobically at pH 3.4 shows persistent high-amplitude respiratory oscillations with a period of about 45 min. These robust autonomous cycles are accompanied by changes of product accumulation (acetaldehyde and acetic acid), intracellular pH, and intracellular redox state, as indicated by continuously monitored NADH fluorescence and the glutathione content of cell-free extracts. Perturbation of the oscillation of dissolved O2 was produced on addition of 100 microM glutathione, > 10 nM Na nitroprusside, 8 microM NaNO2, or 10 microM S-nitrosoglutathione. NO gas, putative NO.-releasing agents, or an inhibitor of NO synthase were ineffective. We suggest that nitrosation by NO+ of a component of a redox switch can account for these data, and we emphasise the different modes of action of the different redox forms of nitrogen monoxide.

Cations↗
PubMed1998

Effects of intermediates of methionine metabolism and nucleoside analogs on S-adenosylmethionine transport by Trypanosoma brucei brucei and a drug-resistant Trypanosoma brucei rhodesiense.

The effects of purine nucleoside analogs, polyamines, and established trypanocidal agents on the uptake of [8-14C]adenosine and S-[methyl-3H]adenosylmethionine (AdoMet) by bloodform trypanosomes of drug-susceptible Trypanosoma brucei brucei and a drug-resistant Trypanosoma brucei rhodesiense clinical isolate were compared. AdoMet uptake was not antagonized by omithine or methionine (500 microM), adenosine (100 microM), or other purine nucleosides, including methylthioadenosine (MTA) at 500 microM. Hydroxyethylthioadenosine (HETA), a trypanocidal analog of methylthioadenosine, and sinefungin, an analog of AdoMet, were competitive with AdoMet transport in both isolates. Dipyridamole, an antagonist of the adenosine P2 transporter, also competed with AdoMet transport in both isolates. The trypanocidal diamidines pentamidine, Berenil, CGP 40215, and the decarboxylated S-adenosylmethionine (dAdoMet) analog MDL 73811 (5'-¿[(Z)-4-amino-2-butenyl]¿methyl-amino¿-5'-deoxyadenosine) competed with P2 adenosine transport but did not inhibit AdoMet transport at 100 microM. Methylglyoxalbis(guanylhydrazone) (MGBG), an analog of dAdoMet, was a strong competitive inhibitor of adenosine transport at 100 microM, but did not inhibit AdoMet transport. The polyamines putrescine, spermine, and spermidine (1 mM) were examined for competition with adenosine and AdoMet transport. Putrescine significantly inhibited P2 adenosine transport in both strains (in the presence of saturating inosine), but AdoMet transport was not affected by these polyamines. P2 adenosine transport in both strains was highly inhibited by melarsen oxide and melamine, its key organic component, whereas AdoMet uptake was not affected by these agents. These findings further characterize distinguishing features of the unique AdoMet transporter in African trypanosomes, and indicate that the P2 adenosine transporter remains functional in melarsen- and diamidine-resistant clinical isolates.

Adenosine↗
PubMed1998

Vision influences tactile perception without proprioceptive orienting.

The perception of tactile stimuli is facilitated when subjects look towards the stimulated body site: this facilitation even takes place when visual information is unavailable, as when orienting in the dark. It is not known whether the facilitation is due entirely to such proprioceptive orienting of eye and head, or whether visual information of the body site can also facilitate touch. An experiment is reported which dissociates vision and proprioception, and demonstrates for the first time that vision of a body part, independent of proprioceptive orienting, can indeed effect somatosensation.

Adult↗
PubMed1998

Oxygen induces fatty acid (n-6)-desaturation independently of temperature in Acanthamoeba castellanii.

Induction of a microsomal oleate delta12 (n-6) desaturase which is mainly responsible for an increase in membrane lipid unsaturation at low temperature has been observed in the free-living amoeba Acanthamoeba castellanii. In this study we show that the enzyme can also be regulated by oxygen independently of temperature in batch cultures grown to O2-limitation. Raising the oxygen concentration from below the lower limit of detection (< 0.1 microM) to approximately air-saturation (230 microM), whilst maintaining the growth temperature constant (30 degrees C), increased lipid unsaturation and elevated n-6-desaturase activity 2.3-fold. Addition of the protein synthesis inhibitor, anisomycin, showed that increased desaturase activity was due to new protein synthesis rather than activation of pre-existing enzyme. These observations are important for future studies of the mechanism of temperature adaptation in poikilotherms.

Acanthamoeba↗
PubMed1998

Circadian and ultradian clock-controlled rhythms in unicellular microorganisms.

The time structure of a biological system is at least as intricate as its spatial structure. Whereas we have detailed information about the latter, our understanding of the former is still rudimentary. As techniques for monitoring intracellular processes continuously in single cells become more refined, it becomes increasingly evident that periodic behaviour abounds in all time domains. Circadian timekeeping dominates in natural environments. Here the free-running period is about 24 h. Circadian rhythms in eukaryotes and prokaryotes allow predictive matching of intracellular states with environmental changes during the daily cycles. Unicellular organisms provide excellent systems for the study of these phenomena, which pervade all higher life forms. Intracellular timekeeping is essential. The presence of a temperature-compensated oscillator provides such a timer. The coupled outputs (epigenetic oscillations) of this ultradian clock constitute a special class of ultradian rhythm. These are undamped and endogenously driven by a device which shows biochemical properties characteristic of transcriptional and translational elements. Energy-yielding processes, protein turnover, motility and the timing of the cell-division cycle processes are all controlled by the ultradian clock. Different periods characterize different species, and this indicates a genetic determinant. Periods range from 30 min to 4 h. Mechanisms of clock control are being elucidated; it is becoming evident that many different control circuits can provide these functions.

Activity Cycles↗
PubMed1998

Acanthamoeba castellanii: growth, encystment, excystment and biocide susceptibility.

Stages in the encystment and excystment processes of Acanthamoeba castellanii have been studied. The kinetics of encystment involved measurements of the three phases (pre-encystment, cyst initiation and cyst wall synthesis). Excystment, starting from a mature cyst, involved pre-emergence, penetration outwards of the cyst wall and free trophozoite. The sensitivity to biocides of trophozoites in the exponential growth phase, pre-encystment trophozoites, mature cysts and pre-excystment cysts has been investigated. Some differences in relative sensitivity to a bisbiguanide (chlorhexidine) and a polymeric biguanide (polyhexamethylene biguanide) were observed, but mature cysts were always the most resistant cellular form.

Acanthamoeba↗
PubMed1998

Quantitative immunohistochemical evidence of a functional gradient of chondroitin 4-sulphate/dermatan sulphate, developmentally regulated in the predentine of rat incisor.

A quantitative examination was carried out on the early and mature stages of dentinogenesis in the rat incisor, using a post-embedding immunogold labelling with an anti-chondroitin 4 sulphate/dermatan sulphate antibody (2B6). At a very early stage of predentine formation, before polarizing odontoblasts have established junctional complexes, immunolabelling was weak. In contrast, when polarized odontoblasts established distal junctional complexes, immunolabelling in predentine was uniform and threefold denser than in initial predentine. The same gold particle density was found in the non-mineralized mantle dentine. During circumpulpal dentine formation, a gradient was seen in predentine, a larger number of gold particles being scored in the proximal zone compared with the distal region adjacent to the mineralization front. In circumpulpal dentine, some labelling was found within the lumen of the tubules and in the bordering dentine around the tubules. A few particles were also detected in intertubular matrix after demineralization. Together, these data provide evidence for a developmentally regulated gradient during the transition between mantle and circumpulpal dentine, and also in a more mature part of the tooth, a functional gradient that probably plays a role in the process of mineralization.

Animals↗
PubMed1998

Biguanide-induced changes in Acanthamoeba castellanii: an electron microscopic study.

Trophozoites and cysts of Acanthamoeba castellanii were exposed to chlorhexidine diacetate (CHA) and polyhexamethylene biguanide (PHMB); changes in cell ultrastructure and surface structure were examined by both transmission and scanning electron microscopy. PHMB caused a greater degree of structural and membrane damage; the cytoplasmic contents were severely depleted and there were clusters of densely stained precipitates on the cell surface. Concentrations of CHA greater than 100 microg ml(-1) produced shrinkage from the cyst wall. At high concentrations, PHMB induced a slight withdrawal of the cytoplasm from the wall and, unlike CHA, induced swelling of the cysts. These findings do not define the mechanisms of action of CHA and PHMB, but provide evidence that a major target site for both agents is the plasma membrane. However, additional intracellular damage undoubtedly contributes to the lethal effects. The greater resistance of cysts may be associated with reduced biguanide uptake.

Acanthamoeba↗
PubMed1998

Investigating relationships between a range of potential indicators of general practice prescribing: an observational study.

OBJECTIVES: (i) to describe the variation in a number of potential prescribing indicators across a large number of general practices, (ii) to determine whether particular indicators are associated with higher or lower overall prescribing costs, (iii) to determine how particular indicators are correlated with each other, (iv) to determine whether the indicators are stable over time. DESIGN: Observational study based on the analysis of PACT (Prescribing Analysis and Cost) data for general practices. SETTING: The Trent region of England. SUBJECTS: 809 general practices. MAIN OUTCOME MEASURES: Variations in a range of potential prescribing performance indicators; correlations between these indicators and NIC (net ingredient costs) per ASTRO-PU (Age, sex and temporary resident originated prescribing unit); change in indicators between the financial year 1994-5 and 1995-6. RESULTS: Wide variations were found between practices in a range of potential prescribing performance indicators. There were positive correlation (P < 0.001) between NIC per ASTRO-PU and indicators of relatively high cost prescribing within different therapeutic areas. There were negative correlations (P < 0.001) with indicators of relatively low cost prescribing. There were positive intercorrelations (P < 0.001) between indicators of relatively high cost prescribing. For most indicators there were significant changes (P < 0.001) in values between the two years. CONCLUSION: There are considerable variations between general practices in prescribing performance indicators and the indicators show changes over time. We have demonstrated correlations between different indicators that lend support to the idea that such indicators might act as proxies for more general prescribing patterns. However, most of the correlations we observed were not strong. Further research is needed into the development and use of indicators based on PACT data.

Drug Prescriptions↗
PubMed1998

Flow cytometric assessment of the postantibiotic effect of methicillin on Staphylococcus aureus.

The postantibiotic effect (PAE) following a 2-h exposure of Staphylococcus aureus NCTC 6571 to methicillin (5x the MIC) was investigated with fluorescent probes, 5-cyano-2,3-di-4-tolyl tetrazolium chloride (CTC), an indicator of respiratory activity, and the membrane potential-sensitive compound bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC4(3)]. Counts of the numbers of CFU on solid agar correlated well with information gained from the CTC and DiBAC4(3) fluorescence intensity distributions obtained by flow cytometry and revealed that the postantibiotic effect was 3.1 h. Due to the capacity of flow cytometry to provide information on the heterogeneity of a bacterial population, both fluorescent probes identified the emergence of an active subpopulation 4 h after removal of the methicillin, indicating the recovery of a small percentage of the population. After removal of the methicillin and resuspension of the cells in methicillin-free medium, a further decrease in the respiratory activity and the membrane integrity of the population was observed, although the CFU counts hardly varied, indicating continued antibiotic-induced damage. Also, CTC fluorescence measurements identified numerous subpopulations during the PAE period; this suggests that the PAE is complex, with individual organisms exhibiting various degrees of recovery. Flow cytometry thus provides a rapid and sensitive alternative to traditional techniques that have been used to study PAE, with the added advantage that physiological changes can be detected as they arise.

Colony Count, Microbial↗
PubMed1998

Carbohydrate and Amino Acid Fermentation in the Free-Living Primitive Protozoon Hexamita sp.

Hexamita sp. is an amitochondriate free-living diplomonad which inhabits O(2)-limited environments, such as the deep waters and sediments of lakes and marine basins. C nuclear magnetic resonance spectroscopy reveals ethanol, lactate, acetate, and alanine as products of glucose fermentation under microaerobic conditions (23 to 34 muM O(2)). Propionic acid and butyric acid were also detected and are believed to be the result of fermentation of alternative substrates. Production of organic acids was greatest under microaerobic conditions (15 muM O(2)) and decreased under anaerobic (<0.25 muM O(2)) and aerobic (200 to 250 muM O(2)) conditions. Microaerobic incubation resulted in the production of high levels of oxidized end products (70% acetate) compared to that produced under anoxic conditions (20% acetate). In addition, data suggest that Hexamita cells contain the arginine dihydrolase pathway, generating energy from the catabolism of arginine to citrulline, ornithine, NH(4), and CO(2). The rate of arginine catabolism was higher under anoxic conditions than under microaerobic conditions. Hexamita cells were able to grow in the absence of a carbohydrate source, albeit with a lower growth rate and yield.

Journal Article↗
PubMed1997

Evolution of the hydrogenosome.

Since its discovery almost 25 years ago the enigmatic hydrogenosome, a redox organelle of anaerobic unicellular eukaryotes, has puzzled evolutionists as to its origin and function. Synthesis of recent molecular, physiological and morphological studies now favours the hypothesis that hydrogenosomes derived from a modification of pre-existing mitochondria, and argues against the previously held view that the hydrogenosome had a polyphyletic origin. These data provide evidence for a more ancient origin of mitochondria than hitherto thought.

Animals↗