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Biomedical subjects

C R Stewart

Publications and source records attributed to C R Stewart.

At least 55 records · Page 3Linked to original sources
PubMed1982

Effects of aminoacetonitrile on net photosynthesis, ribulose-1,5-bisphosphate levels, and glycolate pathway intermediates.

The effects of aminoacetonitrile (a competitive inhibitor of glycine oxidation) on net photosynthesis, glycolate pathway intermediates, and ribulose-1,5-bisphosphate (RuBP) levels have been investigated at different O(2) and CO(2) concentrations with soybean (Glycine max)[L] Merr. cv Pioneer 1677) leaf discs floated on 25 millimolar aminoacetonitrile (AAN) for 50 minutes prior to assay.At 2% O(2) and 200 or 330 microliters per liter CO(2), the inhibitor had no effect on the rate of net photosynthesis and RuBP levels when compared with the control levels. At 11% to 60% O(2), AAN caused a decrease in net photosynthesis in addition to the inhibition by O(2). This extra inhibition ranged from 22% to 59% depending on the O(2) and CO(2) concentrations. The levels of RuBP, however, were 1.3 to 2.7 times higher than in the control plants at the same O(2) concentrations. At 40% O(2) and 200 microliters per liter CO(2), the inhibitor caused a 6-fold increase in glycine and more than 2-fold increase in glyoxylate levels, whereas those of glycolate decreased by approximately one-half.The decrease in net photosynthesis observed with AAN is not the result of the depletion of the RuBP pool due to the lack of recycling of carbon from the glycolate pathway to the Calvin cycle. The higher levels of RuBP caused by AAN in photorespiratory conditions, suggest that RuBP carboxylase was inhibited. Glyoxylate could be a possible candidate for the inhibition of the enzyme but what is known so far about its inhibitory properties in vitro may not fit the existing in vivo conditions. An alternative explanation for the inhibition is proposed.

Journal Article↗
PubMed1981

Submitochondrial location and electron transport characteristics of enzymes involved in proline oxidation.

Isolated corn mitochondria (Zea mays cv. B73 x Mo17) were fractionated and the fragments were separated on a 20-45% (weight/weight) continuous sucrose gradient. Soluble enzymes remained at the top of the gradient overlapping with the outer membranes, while inner membrane vesicles and intact inner membranes were distributed farther down the gradient. Proline oxidase and Delta(1)-pyrroline-5-carboxylic acid dehydrogenase activities were associated only with the inner mitochondrial membrane. Glutamate dehydrogenase was confirmed as a matrix enzyme.Both proline and Delta(1)-pyrroline-5-carboxylic acid supported oxygen uptake in isolated mitochondria. Proline dependent oxygen uptake was relatively independent of pH with a maximum rate at pH 7.2. In contrast, Delta(1)-pyrroline-5-carboxylic acid-dependent oxygen uptake was sensitive to pH with an optimum at pH 6.1. The oxidation of proline and Delta(1)-pyrroline-5-carboxylic acid was inhibited by 10 micromolar rotenone. This indicates that electrons from these substrates enter the respiratory chain prior to at least one of the rotenone sensitive iron-sulfur proteins. Both substrates yielded ADP:O ratios of around 1.9 as compared to malate plus pyruvate (2.1), succinate (1.3), and exogenous NADH (1.2).

Journal Article↗
PubMed1981

Predominance of bacteriophage SP82 over bacteriophage SP01 in mixed infections of Bacillus subtilis.

In mixed infections with Bacillus subtilis phages SP82 and SP01, the SP82 genotype is predominant among the progeny. This predominance is determined by a specific region of the genome, the pos region, which apparently is located near genes 29 to 32 (by the SP01 numbering system). Recombination between SP82 and SP01 yields phage which have both the SP82 pos region and an SP01 mutation. This mutation then behaves in mixed infection as if it were part of an SP82 genome.

Bacillus subtilis↗
PubMed1980

Oxygen and Carbon Dioxide Effects on the Pool Size of Some Photosynthetic and Photorespiratory Intermediates in Soybean (Glycine max [L.] Merr.).

The levels of ribulose 1,5-bisphosphate (RuBP), 3-phosphoglyceric acid (PGA), glycolate, glycine, and serine were measured in soybean leaflets during photosynthesis in atmospheres ranging from 1 to 60% O(2) and from 0 to 500 microliters per liter CO(2.)The RuBP level remained constant as CO(2) concentration was decreased in atmospheres containing 20 or 60% O(2), but increased as CO(2) concentration was decreased in atmospheres containing 1% O(2.) PGA levels decreased at CO(2) concentrations near or below the CO(2) compensation point under all O(2) concentrations. The glycolate pool at 300 microliters per liter CO(2) increased slightly with increasing O(2) concentration, but remained nearly constant at very low CO(2). The serine pool showed no measurable change over the range of CO(2) or O(2) concentrations tested. The glycine pool did not change significantly with varying CO(2) concentration but increased linearly with increasing O(2) concentration.Measured RuBP levels indicate an RuBP concentration less than the estimated concentration of RuBP carboxylase/oxygenase active sites. The constant RuBP pool size in 20% O(2), however, indicates that RuBP level does not limit photosynthesis or photorespiration any more at 50 microliters per liter CO(2) than at 450 microliters per liter.

Journal Article↗
PubMed1980

The Mechanism of Abscisic Acid-induced Proline Accumulation in Barley Leaves.

When leaf blades of fully expanded second leaves of barley (cv. Prior) were excised and incubated with the cut end in a 20 milligram per liter solution of abscisic acid, they accumulated proline at the rate of about 1 micromole per hour per gram fresh weight after a 3- to 4-hour lag. This accumulation occurred reproducibly only if leaves were pretreated by placing the cut end in a solution consisting of 50 millimolar sucrose and 1 millimolar glutamate. Treated leaves were taken from plants which had been in the light for 24 hours.Abscisic acid caused a stimulation of proline synthesis from glutamic acid. Proline oxidation rates were similar in leaves incubated in abscisic acid and in water even though the proline level in abscisic acid-treated leaves was 2.5 times the level in the water-treated controls. The incorporation of proline into protein was not affected by abscisic acid.These results are interpreted to indicate that the metabolic cause of abscisic acid-induced proline accumulation is a stimulation of proline synthesis from glutamic acid. Inhibition of the utilization of proline by oxidation and protein synthesis does not contribute to proline accumulation the way it does in drought-stressed leaves.

Journal Article↗
PubMed1980

Oestradiol in saliva during the menstrual cycle.

Sixteen women provided saliva samples throughout a menstrual cycle and the concentration of oestradiol was measured. Blood samples were taken around mid-cycle and the luteinizing hormone peak was used to diagnose the timing of ovulation. The levels of oestradiol in saliva followed the same pattern as in blood. The peak of oestradiol in saliva could be used to predict accurately the time of onset of the next menstrual period. The analysis of saliva could be useful in the investigation of women in whom serial venepunctures are not possible.

Estradiol↗
PubMed1980

Multiple entrapment neuropathies in depression.

A 72-year-old chronically depressed man developed bilateral ulnar, median, and peroneal nerve palsies. Chronic depression predisposes to pressure neuropathies because of prolonged immobility and because of postures with leg crossings, resting arms on elbows, and resting chin on hyperextended wrist.

Aged↗
PubMed1979

Prenatal diagnosis using amniocentesis: the Christchurch experience.

A service for biochemical analysis of amniotic fluid has been available since 1975. A total of 186 early pregnancy samples were received, the majority were from patients at risk for chromosome abnormalities or neural tube defects. The indications for analysis and the problems related to the results are presented and the need for an established genetic counselling system with a supra-regional assay service is discussed.

Amniocentesis↗
PubMed1978

Factors associated with planned and unplanned nuptial births.

The incidence of unplanned pregnancy in a cohort of 1038 mothers of nuptial children was examined. The major findings were: (1) about one third of the pregnancies were unplanned but there was little evidence that unplanned children were unwanted; (2) there was no evidence to suggest that unplanned birth was related to poor education, low socio-economic status or lack of knowledge of contraception; (3) 40 percent of unplanned births were the result of contraceptive failure; (4) a common denominator in 38 percent of unplanned births was failure or breakdown in the woman's usage of the contraceptive pill.

Contraception↗
PubMed1978

Metabolism of [5-h]proline by barley leaves and its use in measuring the effects of water stress on proline oxidation.

The objective of these experiments was to determine the fate of tritium from the 5 position of proline and to assess the validity of its loss to H(2)O as a measure of proline oxidation. When [5-(3)H]proline was fed to barley (Hordeum vulgare) leaves, tritium was recovered in H(2)O and metabolites such as glutamate, glutamine, organic acids, aspartate, asparagine, and gamma-aminobutyrate. Collectively these metabolites, which are oxidation products of proline, accounted for 8% of the (3)H recovered after 5 hours. In spite of the amount recovered in metabolites, the rates of proline oxidation estimated by measuring (3)H(2)O recovery from [5-(3)H]proline were only slightly lower than rates estimated by incorporation of (14)C into oxidized products and loss of (14)C from total proline. Therefore, (3)H(2)O recovery from [5-(3)H]proline is useful in assessing the effects of stress on proline metabolism.Water stress inhibited proline oxidation, as reported previously. In addition, a reconversion of proline oxidation products to proline occurred in stressed leaves. This observation probably indicates a breakdown in cellular compartmentation of proline synthesis and proline oxidation.

Journal Article↗
PubMed1978

Role of carbohydrates in proline accumulation in wilted barley leaves.

The effect of wilting on proline synthesis, proline oxidation, and protein synthesis-all of which contribute to proline accumulation-was determined in nonstarved barley (Hordeum vulgare L.) leaves. Nonstarved leaves were from plants previously in the light for 24 hours and starved leaves were from plants previously in the dark for 48 hours. Wilted leaves from nonstarved plants accumulated proline at the rate of about 1 mumole per hour per gram of fresh weight whereas wilted leaves from starved plants accumulated very little proline. Wilting caused a 40-fold stimulation of proline synthesis from glutamate in nonstarved leaves but had very little effect in starved leaves. Proline oxidation and protein synthesis, on the other hand, were inhibited by wilting in both nonstarved and starved leaves. Thus, the role of carbohydrates in proline accumulation is to supply precursors for the stimulated proline synthesis. These results further indicate that the main metabolic response causing proline to accumulate in wilted barley leaves is the stimulation of proline synthesis from glutamate. The difference between these results and those obtained with beans is discussed.Wilting caused an increased conversion of glutamate to other products. In nonstarved leaves, conversion to organic acids as well as to proline was increased. In starved leaves, wilting caused an increase in the conversion of glutamate to glutamine, aspartate, asparagine, and organic acids.

Journal Article↗