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D Kerridge

Publications and source records attributed to D Kerridge.

At least 19 recordsLinked to original sources
PubMed1995

A purine permease in Candida glabrata.

Competition experiments revealed that adenine and guanine were transported by a purine permease in both Candida glabrata 4 and a C. glabrata 4 cytosine permease negative mutant. The C. glabrata 4 cytosine permease negative mutant was isolated using 5-fluorocytosine selection. This mutant no longer transported cytosine, but transported adenine and guanine. A transport system for hypoxanthine was not detected. Hence, in addition to the cytosine permease, a purine permease exists in C. glabrata. This differs from the purine cytosine permeases in Saccharomyces cerevisiae and Candida albicans which transport adenine, cytosine, guanine and hypoxanthine.

Adenine↗
PubMed1995

Manometric rhinometry.

A new method of measuring nasal volume is described. It works by extracting air from a closed cavity and measuring the resultant pressure change. To validate this method in the nose, 17 healthy volunteers were examined before and after application of xylometazoline. The apparent volume before decongestion was a mean of 204 ml. After decongestion the average volume was 228 ml. The difference is highly significant (P < 0.01). We conclude that manometric rhinometry is a valid method of investigating the nose and sinuses.

Adult↗
PubMed1995

Manometric rhinometry: a new method of measuring nasal volume.

A new method of measuring the volume of the air space in the nose and sinuses is presented. We have called this method "manometric rhinometry." By closing off the nose anteriorly and posteriorly a closed space is created. A volume of air is then removed and the resultant pressure change is recorded. The original volume is calculated from the pressure change. Twenty adults have been investigated using this method. The volume recorded ranged from 78 to 198 ml (average: 138 ml). Test-retest analysis showed a correlation coefficient of 0.98. In addition, 24 children aged 4 to 12 years were examined. Their volumes were 43 to 198 ml. Test-retest analysis gave a correlation coefficient of 0.94. The significance of these findings is discussed.

Adult↗
PubMed1994

Characterisation of a partially purified uracil phosphoribosyltransferase from the opportunistic pathogen Candida albicans.

This paper describes for the first time the partial purification and properties of uracil phosphoribosyltransferase (UPRTase) from the yeast Candida albicans. UPRTase was purified 38 fold by acid precipitation, DEAE-Sephacel chromatography and ultrafiltration. Further purification of UPRTase was unsuccessful due to the labile nature of the enzyme and the failure in obtaining satisfactory stabilizing conditions. SDS-PAGE suggested that the enzyme exists as a dimer of two dissimilar subunits with molecular masses of 47 and 38 kDa. The pH optimum for phosphoribosylation was about 7.5 and the optimal Mg++ concentration was 2 mM. The kinetics of the enzymes for its substrates, uracil and 5-phosphoribosyl-1-pyrophosphate (PRPP) were determined by measuring initial enzyme velocities over a wide range of concentrations of either substrate at different fixed concentrations of the second substrate. Graphic analysis of the data by Hanes-Woolf plots indicated that the reaction is indistinguishable from a double displacement reaction. 'Ping pong' mechanism has been previously reported for other phosphoribosyltransferases. The enzyme has a low affinity for its substrates (Km = 70.5 and 186 microM for uracil and PRPP, respectively) as compared with those of E. coli and baker's yeast. Inhibition studies indicate that 5-fluorouracil acts as an alternative substrate for UPRTase with 1.6 times higher specific activity.

Candida albicans↗
PubMed1990

Pathogenicity of 5-fluorocytosine resistant strains of Candida albicans.

Mutants of Candida albicans blocked in pyrimidine transport and salvage metabolism were produced by a two step mutagenic procedure and selected by their resistance to 5-fluorocytosine (flucytosine). The growth rates and growth yields of these mutants did not differ significantly from the parental strain of C. albicans. Examination of their pathogenicity to mice demonstrated that a defect in the uridine transport function decreased the pathogenicity of C. albicans.

Animals↗
PubMed1990

Uptake of pyrimidines and their derivatives into Candida glabrata and Candida albicans.

The uptake of pyrimidines and their derivatives into Candida glabrata and Candida albicans was measured using a novel technique in which the cells were rapidly separated from their suspending medium by centrifugation through a layer of an inert oil. The uptake of [14C]cytosine was linear for 30 s for all concentrations of pyrimidine tested. In C. glabrata but not C. albicans cytosine transport was mediated by both a high affinity (Km 0.8 +/- 0.1 microM), low capacity [V 40 +/- 4 pmol (microliters cell water)-1 s-1] and a low affinity [Km 240 +/- 35 microM], high capacity system [V 770 +/- 170 pmol (microliters cell water)-1 s-1]. The cytosine permease in C. glabrata was specific for cytosine and 5-fluorocytosine. In C. albicans there was only one cytosine transport system [Km 2.4 +/- 0.3 microM; V 50 +/- 4 pmol (microliters cell water)-1 s-1]; this system also transported adenine, guanine and hypoxanthine. Differences in nucleoside transport were also observed for C. glabrata and C. albicans, with the uridine permease in C. glabrata transporting only uridine and 5-fluorouridine whereas cytidine and adenosine were also transported by the uridine permease in C. albicans. Studies on the effect of nucleoside analogues on uridine transport in C. glabrata demonstrated the importance of the sugar moiety in determining the specificity of transport, with a hydroxyl residue on C-2 being apparently essential for transport.

Biological Transport↗
PubMed1990

19F nuclear magnetic resonance study of fluoropyrimidine metabolism in strains of Candida glabrata with specific defects in pyrimidine metabolism.

Flucytosine (5-FC)-resistant strains were isolated from the haploid opportunistic pathogen Candida glabrata by UV-induced mutation and fluoropyrimidine selection. These strains were characterized biochemically, and the metabolism of fluorinated pyrimidines was studied by 19F nuclear magnetic resonance spectroscopy. No evidence was obtained from these studies for degradative metabolism of the fluorinated derivatives. In the parental susceptible strain of C. glabrata, 5-fluorouracil but not 5-FC was detected within the cells. 5-Fluorouracil was also present in the culture supernatant after incubation of the cells with 5-FC. The distribution of fluorinated derivatives within the 5-FC-resistant strains was consistent with their genotype. Two strains of C. glabrata which had only a partial loss of cytosine deaminase and UMP pyrophosphorylase activity had high levels of resistance to 5-FC. Both C. glabrata and Candida albicans were susceptible to 5-fluorouridine. This compound but not the anticancer drug 5-fluoro-2-deoxyuridine was shown to be transported into susceptible cells by a specific uridine permease.

Candida↗
PubMed1989

Correlation of inhibition of sterol synthesis with growth-inhibitory action of imidazole antimycotics in Candida albicans.

The effect of tioconazole and other imidazole antimycotics on both growth and sterol biosynthesis by Candida albicans and C. pseudotropicalis in tube culture was investigated. Trailing endpoints were only seen in statically incubated cultures, but the final MIC, i.e. that giving complete inhibition of growth, was similar in both static and shaken cultures. Desmethylsterol biosynthesis was equally sensitive to the inhibitory action of tioconazole in both shaken and static cultures and the trailing endpoints in the latter coincided with this inhibition. Poor inhibitors of ergosterol biosynthesis did not show the trailing phenomenon but did show a conventional MIC. The inhibition of sterol biosynthesis, unlike that of growth, was not subject to an inoculum effect. As others have found, ergosterol was unable to antagonize the effects of tioconazole on C. albicans and this was probably due to lack of uptake of this sterol. In contrast to C. albicans, the Gram-positive bacterium, Staphylococcus aureus H, which lacks membrane sterols, showed no trailing endpoints with tioconazole after either shaken or static incubation.

Antifungal Agents↗
PubMed1988

Correlation between the sterol composition of membranes and morphology in Candida albicans.

The opportunistic pathogenic fungus Candida albicans was examined in three distinct morphological forms: yeast, mycelia, and stunted mycelia obtained by growing cells under mycelial-inducing conditions in the presence of ketoconazole at concentrations below the MIC. Comparison of the sterols of the parental strain with those from a mutant unable to produce mycelia, by TLC and GLC, showed no significant differences in sterol composition between the yeast and mycelial morphological forms. However, ketoconazole-treated cells possessed a lower ergosterol content and an increased amount of 14-methylated sterol precursors. The effect of ketoconazole on mycelial cells was quantitatively different from the effect on yeast cells in that the ratio of 4, 14-dimethylsterols to 4-methylsterols was significantly lower in the stunted mycelial morphological forms. A comparison of the effect of terbinafine on sterol biosynthesis and morphology suggests that the effect on ergosterol content is of greater importance than the increase in sterol precursors in determining cell shape.

Candida albicans↗
PubMed1987

Isolation of mutants of Candida glabrata resistant to miconazole.

Elucidation of the mode of action of azole antifungals would be aided by studying resistant mutants. It is difficult to obtain mutants of Candida albicans in the laboratory, and there have only been a few studies on clinical isolates which seem to be resistant because of impaired drug uptake. C. glabrata, unlike C. albicans, is haploid and more likely to give rise to resistant variants. Over 30 mutants have been isolated by selection with miconazole on solid medium and have MICs of miconazole about ten times that of the parental strain. One such mutant has a reduced growth rate and final cell yield. In intact cells, ergosterol biosynthesis is tenfold less sensitive to miconazole than in the parent. However, uptake of [3H]miconazole by cells is identical in both strains. The significance of these observations is discussed.

Amino Acids↗
PubMed1986

Drug resistance in the opportunistic pathogens Candida albicans and Candida glabrata.

There are three major classes of antifungal drug used to treat patients suffering from topical and systemic infections caused by Candida albicans. Both the polyene macrolide antibiotics and the synthetic imidazole derivatives interact with membranes of sensitive organisms causing an impairment of function and cessation of growth. It is possible to obtain mutants of C. albicans resistant to these drugs but they are not a clinical problem. This may result from the fact that the organism is diploid with no haploid stage in its life cycle and the interaction of these compounds with their target is complex involving a number of membrane constituents. In contrast the occurrence of strains of C. albicans resistant to 5-fluorocytosine is a serious clinical problem. Here partial resistance is associated with heterozygosity at the locus coding for UMP pyrophosphorylase. Mitotic segregation can give rise to homozygous resistance in strains where the enzyme is completely absent. This is analogous to acyclovir resistance in herpes simplex virus where resistance is associated with loss of the virus encoded thymidine kinase.

Antifungal Agents↗
PubMed1986

A 19F nuclear magnetic resonance study of uptake and metabolism of 5-fluorocytosine in susceptible and resistant strains of Candida albicans.

The metabolism of the antifungal drug 5-fluorocytosine (5-FC) was studied in intact viable cells of Candida albicans by 19F nuclear magnetic resonance (NMR). The uptake of the drug and its conversion to the deaminated product 5-fluorouracil (5-FU) were easily observed by NMR analysis of both the cells and the supernatants of the incubation mixture. In the 5-FC-resistant mutant D14 of C. albicans, which lacked cytosine deaminase activity, the resonance peak of 5-FU was not observed. In intact cells of all 5-FC-susceptible strains the metabolism of 5-FU progressed to the formation of other fluorinated derivatives which were visualized as a single, broad resonance band at a lower field with respect to 5-FC and 5-FU. This band was resolved into three distinct peaks in the acid extract of treated cells, one of these peaks being attributable to 5-fluoro-dUMP (5-FdUMP). In strain 72R of C. albicans, which is 5-FC resistant because of a low level of UMP-pyrophosphorylase activity, the broad, low-field resonance band was detected later and with much less intensity than in the 5-FC-sensitive strains. This suggests that, besides 5-FdUMP, this band is also contributed to by 5-FUMP and possibly other phosphorylated derivatives. 19F NMR analysis also revealed that a significant amount of 5-FU is secreted into the external medium, the rate of secretion being higher in 5-FC-resistant strain 72R than in 5-FC-sensitive strain 72S. Although not all resonances were definitely identified, this study shows that 19F NMR spectroscopy may be an important tool for noninvasive analysis of the metabolism of fluorinated drugs in yeasts.

Candida albicans↗