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M Guerin

Publications and source records attributed to M Guerin.

At least 37 records · Page 2Linked to original sources
PubMed1988

Modifications of oxidative phosphorylations in mitochondria isolated from a mutant of Saccharomyces cerevisiae. Possible alterations of the phosphate transport.

Mutants of Saccharomyces cerevisiae were isolated which supported two unlinked nuclear mutations conferring thermosensitivity and cold sensitivity respectively, and a mitochondrial one conferring paromomycin sensitivity. Mitochondria isolated from such a mutant exhibited modifications of several phosphate-requiring functions: (a) kinetic parameters of the phosphate dependence of ATP synthesis were modified; (b) in the absence of phosphate the inner mitochondrial membrane exhibited a high proton leakage; (c) mutant mitochondria always exhibited a poor respiratory control and required tenfold more phosphate to reach a maximal state 3 of respiration; (d) phosphate transport, as measured by swelling experiments, was mersalyl-insensitive and, consequently, state 3 of the respiration and ATP synthesis remained less mersalyl-sensitive than in wild-type mitochondria. Analysis of the mitochondrial metabolism of diploid and segregant strains indicates that these modifications are related to the cryosensitive phenotype; however, at present, a cooperative effect of the mitochondrial mutation cannot be eliminated. It is proposed that the phosphate carrier itself or a regulatory element was modified.

Adenosine Triphosphate↗
PubMed1988

Comparative studies on the glycolytic and hexose monophosphate pathways in Candida parapsilosis and Saccharomyces cerevisiae.

Some enzymatic activities of the glycolytic and hexose monophosphate pathways of Candida parapsilosis, a yeast lacking alcohol dehydrogenase but able to grow on high glucose concentrations, were compared to those of Saccharomyces cerevisiae. Cells were grown either on 8% glucose or on 2% glycerol and activities measured under optimal conditions. Results were as follows: glycolytic enzymes of C. parapsilosis, except glyceraldehyde 3-phosphate dehydrogenase, exhibited an activity weaker than that of S. cerevisiae, especially when yeasts were grown on glycerol. Fructose-1,6 bisphosphatase, an enzyme implicated in gluconeogenesis and in the hexose monophosphate pathway, and known to be very sensitive to catabolite repression in S. cerevisiae, was always active in C. parapsilosis even when cells were grown on 8% glucose. However, the allosteric properties towards AMP and fructose-2,6-bisphosphate were the same in both strains. Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, two other enzymes of the hexose monophosphate pathway, exhibited a higher activity in C. parapsilosis than in S. cerevisiae. Regulation of two important control points of the glycolytic flux, phosphofructokinase and pyruvate kinase, was investigated. In C. parapsilosis phosphofructokinase was poorly sensitive to ATP but fructose-2,6-bisphosphate completely relieved the light ATP inhibition. Pyruvate kinase did not require fructose-1,6-bisphosphate for its activity, and by this way, did not regulate the glycolytic flux.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1988

c-Ha-ras-1 polymorphism in human breast carcinomas: evidence for a normal distribution of alleles.

Analysis of the c-Ha-ras-1 locus for restriction fragment length polymorphism was determined by Southern blot hybridization in 112 specimens of primary breast carcinoma. Normal cell samples were lymphocytes obtained from 61 of these breast cancer patients and from 62 healthy donors. Our data indicate that the distribution of c-Ha-ras-1 alleles in breast carcinoma patients did not significantly differ from that found in normal individuals. In addition the loss of one allele detected in 5 tumor samples was not correlated to the aggressiveness of breast cancer. Consequently our data imply that hereditary predisposition to breast cancer is not associated with the c-Ha-ras-1 polymorphism as previously reported.

Alleles↗
PubMed1988

[The expression of c-myb is strongly associated with the presence of estrogen and progesterone receptors in breast cancer].

The c-myb gene was studied in 112 breast cancers. c-myb and estrogen receptor (ER) transcripts were found in 78 (70%) and 71 (63%) cancers respectively. Of these 71 ER positive cancers, 64 (90%) contained c-myb transcripts and of the 41 ER negative cancers, 27 (66%) did not contain c-myb mRNA. Our data show that c-myb transcripts are strongly associated with ER and progesterone receptors (p less than 10(-4) status in breast cancer. Thus the c-myb expression could be associated with breast cancers of better prognosis and its analysis could allow a better characterization of new subsets of hormono-dependent cancers responding more efficiently to hormonotherapy.

Breast Neoplasms↗
PubMed1987

The energetic growth yields of the yeast Candida parapsilosis.

The energetic growth yields of Candida parapsilosis were compared with those of Saccharomyces cerevisiae as a function of the energy source in the presence or absence of antimycin A, an inhibitor of the second phosphorylation site. When glycerol was used as energy source, the energetic growth yields were quite similar in C. parapsilosis and S. cerevisiae. On the other hand, when experiments were carried out with glucose as energy source, although three phosphorylation sites were available, glucose was found to be a poor energy source for C. parapsilosis. When C. parapsilosis was grown in the presence of antimycin A, on glucose: YGluS = 3YGlu + AS and on glycerol: YGlyS = 2 YGly + AS. It was concluded that growth in the presence of antimycin A could occur due to the functioning of the third phosphorylation site. This result agrees with previous works indicating that in C. parapsilosis the alternative pathway merges into the main respiratory chain at the cytochrome c level. Although the doubling time of C. parapsilosis was much less temperature-sensitive than that of S. cerevisiae, the energetic growth yield was the same at 13 degrees C and 28 degrees C, and consequently, the secondary pathway did not seem to be thermogenic.

Antimycin A↗
PubMed1987

For calculating osmolality, the simplest formula is the best.

Plasma osmolalities were measured in 100 normal, 100 general hospital and 100 intensive care patients, and compared with the osmolalities calculated from the plasma concentrations of sodium, potassium, glucose and urea, using five different published formulae. The mean osmolar gaps in the 100 consecutive intensive care patients and the 100 general hospital patients were not significantly different from the mean osmolar gap in the 100 normal individuals. The formula which gave the least difference between the measured and calculated osmolality was 2 X Na + urea + glucose, where the concentrations of sodium, urea and glucose were measured in mmol/l.

Adult↗
PubMed1986

Resistance of Candida parapsilosis to drugs.

Several strains of Candida parapsilosis, isolated independently in our laboratory, had their resistance compared to a series of inhibitors which act either at the level of mitochondrial ribosomes (chloramphenicol, erythromycin, paromomycin) or at the level of mitochondrial respiration and oxidative phosphorylation (oligomycin, antimycin A, diuron, carbonylcyanide m-chlorophenylhydrazone). Cells were grown on glycerol media supplemented with one of these inhibitors, and it was demonstrated that the resistance of these yeasts to a large spectrum of antibiotics was due to several features: a resistance to oligomycin was found at the permeation level; the resistance to the other drugs was correlated to the relative insensitivity of cytochrome biosynthesis to the drugs; the cells developed, at the same time, two types of alternative pathways: the one branched at the ubiquinone level which drove electrons from Krebs cycle substrates to oxygen, and the other, antimycin A-insensitive but inhibited by amytal, salicylhydroxamic acid and high cyanide concentrations. This secondary mitochondrial pathway, driving reducing equivalents from cytoplasmic NADH to cytochrome c and then to cytochrome aa3 or to alternate oxidase, allowed the growth of Candida parapsilosis on a non fermentescible medium, supplemented with these drugs.

Antimycin A↗
PubMed1982

New mutants resistant to glucose repression affected in the regulation of the NADH reoxidation.

Spontaneous mutants resistant to vanadate, arsenate or thiophosphate were isolated from a haploid strain of Saccharomyces cerevisiae. These three anions have an inhibitory effect on some mitochondrial functions and at the level of glyceraldehyde 3-phosphate dehydrogenase, a glycolysis enzyme. All the selected mutants had the same phenotype: they were deficient in alcohol dehydrogenase I, the terminal enzyme of the glycolysis, and possessed a high content of cytochrome c oxidase, the terminal enzyme of the respiratory chain. Moreover, cytochrome c oxidase biosynthesis had become insensitive to the catabolite repression, while the biosynthesis of the other enzymes sensitive to this phenomenon were always inhibited by glucose. Metabolic effects of this pleiotropic mutation manifested themselves in the following ways. 1. Growth rate and final cell mass were enhanced, compared to the wild type, when cells were grown on glucose or on glycerol, but not on lactate or ethanol. 2. Growth under anaerobiosis was nil and mutants did not ferment. 3. Mitochondrial respiration of the mutant strains was identical to the wild type with succinate or 2-oxo-glutarate as substrate, and weak with ethanol. But with added NADH, respiration rate of the mutants was higher than that of the wild type and partially insensitive to antimycin, even when cells were grown in repression conditions. It is postulated that in mutants strains, NADH produced at the level of glyceraldehyde 3-phosphate dehydrogenase, failing to be reoxidized via alcohol dehydrogenase, could be reoxidized with a high turnover owing to the enhancement of the amount of cytochrome c oxidase. Since NADH reoxidation is partially insensitive to antimycin, a secondary pathway going from external NADH dehydrogenase to cytochrome c oxidase is suggested.

Alcohol Oxidoreductases↗
PubMed1979

Screening of newborn infants for hypothyroidism. Two years' experience in South Autralia.

Over a period of two years, 40,000 newborn infants in South Australia have been screened for congenital hypothyroidism by the measurement of thyroxine and, on selected samples, of thyroid stimulating hormone. Samples were those obtained for an established newborn screening programme in the State. Eight infants with hypothyroidism were detected; in seven, this was due to congenital agenesis of the thyroid gland and one infant had residual thyroid tissue. A further three sick infants had abnormalities of thyroid function; in two, this was transient and reverted to normal after several weeks and the third infant died. Three infants had thyroxine-binding globulin deficiency.

Congenital Hypothyroidism↗
PubMed1979

The reversible replacement of internal potassium by caesium in isolated turtle heart.

1. By perfusing the isolated turtle heart with Cs solution, most of the intracellular K can be replaced by Cs. After 3--4 hr, Cs approaches a steady-state distribution with a concentration slightly below initial K concentration. 2. During the initial stages of perfusion, the heart accumulated Cs and lost K, the exchange ratio of K for Cs was estimated to be about 0.6. Subsequently perfusion yielded an equi-ionic substitution of K by Cs. 3. In presence of DNP (2 x 10(-4) M), K efflux and Cs accumulation increased but the low initial K--Cs exchange was abolished. Then, the replacement of K by Cs took place at a ratio of K:Cs of about 0.8. Ouabain (10(-5) M) suppressed uptake of Cs whereas K loss was the same as with DNP. 4. These results confirm that permeability of the cardiac sarcolemma to Cs is low, and suggest that the movement of Cs must be mainly attributed to its active transport into cells by the ionic exchange which normally transports K+ and is coupled to the extrusion of Na. The initial low net K efflux could be explained by an accumulation process which facilitates retention of K by the heart. A mechanism of this kind would be described as active reabsorption of some K present in extracellular space and would consequently reduce the uptake of Cs. 5. After loading the heart with Cs, perfusion with K solution showed the exchange of Cs for K at a ratio of Cs:K of about 0.5. K reaccumulation is reduced by ouabain (10(-5) M) and comes back to a normal steady-state distribution after 5 hr. At this time, K concentration was slightly below normal K value, but only half Cs content was eliminated. After 15 hr of perfusion, intracellular K remained constant whereas 15% of the original Cs remained.

Animals↗
PubMed1978

Phosphate transport in yeast mitochondria: purification and characterization of a mitoribosomal synthesis dependent proteolipid showing a high affinity for phosphate.

It is possible to obtain from yeast mitochondria a proteolipid able to bind phosphate, by two different procedures. One of them, generally used for lipid extraction, leads to the preparation of a more active crude proteolipid. This crude proteolipid has been purified by various chromatographic procedures and the active fraction, in phosphate binding, is always associated with cardiolipin. Its molecular weight seems to be close to 10000. The phosphate binding shows ligand saturation behavior and is inhibited by arsenate and N-ethylmaleimide; succinate is noninhibitory. This protein seems to be dependent on the mitoribosomal synthesis since it is not present in mitochrondria of mutant "petite colonie" and its amount largely decreases in mitochondria from yeast grown in the presence of chloramphenicol. It is possible to extract a proteolipid from the oligomycin sensitive ATPase, showing the same activity and properties. The hypothesis that this proteolipid acts as a part of the Pi carrier and constitutes the oligomycin-sensitive ATPase complex is discussed.

Adenosine Triphosphatases↗