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Biomedical subjects

J A Barnett

Publications and source records attributed to J A Barnett.

At least 19 recordsLinked to original sources
PubMed1992

Some controls on oligosaccharide utilization by yeasts: the physiological basis of the Kluyver effect.

Many yeasts can aerobically catabolize exogenously supplied glycosides that are hydrolysed in the cytosol, but few do so anaerobically. This is so, even for yeasts that use one or more of the component hexoses anaerobically. The phenomenon, called the Kluyver effect, appears to be brought about by a combination of the following four factors: (i) fast transport of the glycosides into the cells involves proton symport and seems to require aerobiosis, so, under anaerobic conditions, the glycosides enter the cells much more slowly. This is probably because there is less ATP produced anaerobically than aerobically and, consequently, insufficient to supply the proton pump optimally, which is necessary to maintain proton symport; (ii) in addition, anaerobically, the transport carrier may have a lower substrate affinity; (iii) glycosidases generally have low substrate affinities; and (iv) the consequence of (i), (ii) and (iii) is a lowering of glycolytic flux and this deactivates pyruvate decarboxylase.

Aerobiosis↗
PubMed1992

Regulation of sugar utilization by Saccharomyces cerevisiae.

There are several kinds of regulation that enable microbes to cope with rapidly changing supplies of nutrients. This is exemplified by sugar metabolism in Saccharomyces cerevisiae. Some readily reversible controls affect the activity of enzymes, either by allosteric activation and deactivation, which often occur within seconds, or by covalent modification, within minutes. Other controls regulate the amount of enzyme present in the cells, either by irreversible proteolytic inactivation of the enzyme, or by influencing enzymic synthesis. The nomenclature of these processes is often confused.

Gene Expression Regulation, Enzymologic↗
PubMed1991

Levels of activity of enzymes involved in anaerobic utilization of sugars by six yeast species: observations towards understanding the Kluyver effect.

The activities of pyruvate decarboxylase, alcohol dehydrogenase and certain glycosidases were measured for six species of yeast. Five of these yeasts could utilize one or more disaccharides aerobically, but not anaerobically, although all could use D-glucose anaerobically. That is, each of the five showed the Kluyver effect; but the sixth yeast, Saccharomyces cerevisiae, did not do so. When grown on a glycoside with which it gave the Kluyver effect, each yeast had much less pyruvate decarboxylase activity than when grown on D-glucose or another glycoside. There was no consistent corresponding lowering of activity of either alcohol dehydrogenase, or of the appropriate glycosidase. Hence, pyruvate decarboxylase may have a role in producing the Kluyver effect.

Alcohol Dehydrogenase↗
PubMed1991

Lipopolysaccharide and opioids activate distinct populations of Mytilus edulis immunocytes.

Studies in Mytilus edulis have indicated that immunoregulatory activities comparable to those in vertebrates also exist in invertebrates. Mytilus immunocytes resemble cells of the vertebrate monocyte/macrophage lineage and are activated by similar substances. We searched for differential effects of opioids on these cells in comparison with those of lipopolysaccharide (LPS), in order to determine if different subpopulations of immunoactive hemocytes are involved. We showed that Mytilus immunocytes respond to LPS in a fashion similar to that in vertebrate granulocytes by flattening, and increasing in cellular perimeter and mobility, that LPS administered in vivo results in a lowering of the number of free hemocytes that can be obtained from the animal, and that distinct immunoactive cell populations seem to exist since apparently different subsets of cells react when exposed to LPS or opioids and the opioid antagonist naloxone.

Animals↗
PubMed1991

LPS stimulated invertebrate hemocytes: a role for immunoreactive TNF and IL-1.

Mytilus edulis hemocytes have similarities with vertebrate monocyte/macrophages. We have recently shown that they respond to human TNF and IL-1. We tested the possibility that Mytilus hemocytes produce similar substances in response to LPS. We show that Mytilus hemocytes respond to LPS in a fashion similar to vertebrate monocytes and macrophages and that these responses are inhibited by antibodies to TNF and/or IL-1. These findings are demonstrated both in vitro and in vivo.

Animals↗
PubMed1989

Lack of effect of treatment with human recombinant-tumour necrosis factor (HrTNF) on the binding of quinidine to alpha 1-acid glycoprotein (AGP).

Tumour necrosis factor (TNF) is known to be a key mediator in the acute phase response and its administration has been shown to cause a five fold increase in serum alpha 1-acid glycoprotein (AGP) concentration in the rat. Since, in man, plasma AGP level determines the protein binding of many important drugs (e.g. narcotic analgesics, phenothiazines, antiarrhythmics, calcium channel blockers) likely to be given to patients who will be treated with TNF, it is important to determine if TNF treatment of humans causes a similar increase in AGP concentration and drug binding. Therefore, the plasma protein binding of quinidine and the serum level of AGP were studied over a 4 day period in each of five cancer patients who were treated with human recombinant-tumour necrosis factor (HrTNF) using a dosage schedule of 6-8 x 10(+5) units/m2 daily for 5 days. It was observed that the quinidine binding ratio (the quotient of bound and free concentration in plasma) was highly correlated with the plasma concentration of AGP (r = 0.818) and that the mean pretreatment AGP concentration in the patients was about three times that found in normal subjects. However, no effects of the TNF treatment regime used in the present study could be demonstrated on either plasma AGP concentration or quinidine free fraction. These observations allow the tentative conclusion that HrTNF does not cause a significant increase in serum AGP level in cancer patients whose baseline AGP concentration is high. However, further study of the relationship between TNF treatment and serum AGP level is needed.

Adult↗
PubMed1982

The construction by computer of a diagnostic key to the genera of yeasts and other such groups of taxa.

Groups of taxa such as genera, or groups derived from some forms of cluster analysis, may have insufficient test results that are constant within the groups to allow diagnostic keys and tables to be constructed in the usual way. This paper describes how the usual methods can be adapted to allow construction based on information about the individual group members, instead of on the overall group information. A new key to the genera of yeasts is constructed by these modified methods.

Computers↗
PubMed1976

Some physiological observations on the uptake of D-glucose and 2-deoxy-D-glucose by starving and exponentially-growing yeasts.

Some methods for measuring the uptake of sugars by yeasts were investigated critically. A study was made of the effects of starvation of Pichia pinus, Candida utilis, Saccharomyces cerevisiae and Rhodosporidium toruloides on their uptake of D-glucose and 2-deoxy-D-glucose. Marked changes in the rates of uptake of these sugars occured during 10 h of starvation, including (a) an immediate increase of up to 75% above that for growing cells and (b) a continuous decline to as little as 4%. Each yeast behaved differently. The rates did not remain constant during the periods of starvation often used for studies on the transport of sugars into yeasts. For Pichia pinus, there were striking differences, associated with starvation, between the transport of 2-deoxy-D-glucose and D-glucose, despite evidence that the two sugars enter this yeast by means of the same carrier. Some physiological explanations for these findings are discussed.

Biological Transport↗
PubMed1976

A note on the kinetics of uptake of D-glucose by the food yeast, Candida utilis.

Unlike other yeasts so far investigated, the D-glucose carrier of Candida utilis (strain NCYC 737) appears to change affinity for D-glucose according to its exogenous concentration. When the concentration of D-glucose was less than 0.4 mM, the apparent Km approximately 0.2 mM; at greater than 0.4 mM, the Km approximately 10 mM.

Biological Transport↗
PubMed1976

Evaluation of antibiotic efficacy using electron microscopy: morphological effects of guanylureido cephalosporin, BL-P1654, and carbenicillin on Escherichia coli.

Early response of Escherichia coli to minimal inhibitory concentrations of 112883, BL-P1654, and carbenicillin was determined by [(14)C]leucine uptake and scanning electron microscopy morphology studies. [(14)C]leucine uptake was inhibited later by carbenicillin than by BL-P1654 or 112883. Cellular swelling at 30 min, septal region swelling, and lysis were the progressive morphological changes with BL-P1654 and 112883. Carbenicillin-treated cells showed septal region swelling, beaded chains, and lysis.

Carbenicillin↗
PubMed1975

The entry of D-ribose into some yeasts of the genus Pichia.

The utilization of D-ribose by yeasts of the genus Pichia was examined with respect to aerobic growth, respiration and entry of ribose into the cells. Pichia etchellsii (CBS2011) could respire D-ribose, but not use it for aerobic growth. Pichia fermentans (CBS187) neither respired nor grew on D-ribose, though it entered the cells of this yeast either by simple diffusion, or possibly, by the D-glucose carrier, this having a very low affinity for D-ribose. Pichia pinus (CBS5097) respired and grew on D-ribose; kinetic evidence is given for this yeast having two ribose carriers, one inducible and the other constitutive.

Aerobiosis↗