Biomedical subjects
Publications and source records attributed to J A Barnett.
Through the discovery of Buchner, Biology was relieved of another fragment of mysticism. The splitting up of sugar into CO2 and alcohol is no more the effect of a "vital principle" than the splitting up of cane sugar by invertase. (Jacques Loeb 1906 [138] p.22.)
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Doubling times were measured during exponential growth of 19 strains belonging to 10 of the 17 species of the yeast genus Kluyveromyces. Growth was in shaken aerobic batch culture at 25 degrees C, in a chemically defined medium with D-glucose as sole carbon source. Doubling times were strikingly uniform, being mainly between 2 and 3.5 h.
We propose a pair of population genetic models for a modifier-of-imprinting locus for which different genotypes imprint different proportions of an imprintable target locus in their gametes. The two models examine the situations in which imprinting is advantageous, and we discuss three cases for which the modifier is respectively partially dominant, dominant, or recessive. The models predict the stable equilibrium frequencies of the mutant modifier and functionally diploid individuals in a large population in terms of up to four parameters: the mutation rate at the modifier locus, nu; the selection coefficient against the disadvantageous phenotype, sigma; the proportion of unimprinted eggs produced by homozygotes for the mutant modifier, theta, and, in the partially dominant models, the dominance parameter, kappa. The equilibrium frequency of the mutant phenotypes is shown to be approximately twice that of standard Mendelian models: 2 nu/sigma or 4nu/sigma when the modifier is recessive or dominant, respectively. Mathematical equivalences between these and nonimprinting models are noted.
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.
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.
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.
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.
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.
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.
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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.
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.
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.