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Biomedical subjects

C R Stewart

Publications and source records attributed to C R Stewart.

At least 91 records · Page 5Linked to original sources
PubMed1973

Proline Uptake and Utilization by Chlorella pyrenoidosa.

Conditions for proline uptake and utilization by Chlorella pyrenoidosa Chick are described. Proline is taken up by growing cultures during late log phase growth after depletion of glucose from the medium. However, proline uptake by stationary phase cultures requires the presence of glucose in the medium. The results are consistent with the interpretation that some carbohydrate is required for proline uptake but proline uptake is inhibited by the accumulation of intracellular carbohydrates.Metabolism of proline was by incorporation into protein and oxidation to CO(2) by conversion to glutamic acid and subsequent metabolism of the carbon by the Krebs cycle.

Journal Article↗
PubMed1972

Effects of proline and carbohydrates on the metabolism of exogenous proline by excised bean leaves in the dark.

Proline was metabolized when vacuum infiltrated into starved bean (Phaseolus vulgaris L.) leaves from plants previously in the dark for 48 hours, but an equivalent increase in protein proline was not observed. When (14)C-proline was infiltrated into starved leaves, a large percentage of the (14)C was recovered in other amino acids, organic acids, and CO(2), in addition to that recovered as protein proline. However, extensive oxidation of proline was observed only if enough proline was added to increase substantially the endogenous concentration of proline. Increasing the endogenous concentration did not affect the amount of proline that was incorporated into protein.When added to leaves from plants previously in the light of near saturating intensity for more than 16 hr, very little (14)C-proline was oxidized, even when a sufficient amount of proline was added to increase the endogenous concentration. Adding sucrose to starved leaves along with the proline slowed down the oxidation of proline. Thus, it appears that some carbohydrate or intermediate of carbohydrate metabolism may inhibit the oxidation of proline in leaves.Based on kinetics of labeling, the pathway of proline oxidation was by conversion to glutamic acid and subsequent metabolism to intermediates in the Krebs cycle and to CO(2).

Journal Article↗
PubMed1972

Proline Content and Metabolism during Rehydration of Wilted Excised Leaves in the Dark.

Excised bean (Phaseolus vulgaris) leaves were used to measure changes in proline content and proline metabolism during rehydration in the dark after the leaves had been incubated in the dark 24 hours in a wilted condition.The increase in nonprotein proline which occurs in wilted leaves stopped immediately upon rehydration, and thereafter levels of proline declined. The rate of decline and the fate of the metabolized proline depended on the amount of carbohydrate present. When the level of carbohydrate was relatively high, the rate of decline in proline content was slow, and the proline was converted mainly to protein proline. When the level of carbohydrate was relatively low, the rate of proline decline was rapid and a large percentage of the proline was oxidized to CO(2) and other amino acids in addition to conversion to protein proline.The results indicate that nonprotein proline can be oxidized when the level is increased by endogenous synthesis. Proline oxidation has been observed when the levels are increased by adding exogenous proline. Oxidation of endogenous proline is inhibited by carbohydrates in the leaf, as is true of oxidation of exogenous proline.

Journal Article↗
PubMed1971

Some characteristics of the uptake of glutamine by corn scutellum.

Slices of corn scutellum were used to study amino acid uptake, a natural function of this tissue. The uptake of glutamine was found to be inhibited by several monovalent cations. The accompanying anion did not affect the inhibition. Divalent cations stimulated glutamine uptake, particularly at high glutamine concentrations. The inhibition by monovalent cations was reversed by divalent cations.There was a broad pH optimum (4.3-5.2), and a wide range of pH values over which substantial rates of glutamine uptake were observed (3-7).Seventeen protein amino acids were tested for their effects on glutamine uptake. l-Alanine, l-cysteine, l-glutamic acid, glycine, l-serine, and l-methionine were the only inhibitory amino acids. The inhibition by alanine and methionine was overcome at high glutamine concentrations whereas the inhibition by monovalent cations was not. The inhibition by amino acids was not reversed by divalent cations. d-Alanine and d-methionine had no effect on glutamine uptake.High concentrations of sucrose (0.5 m) did not affect glutamine uptake. Thus, osmotic shock did not cause a dissociation of a transport protein from a membrane. Mannose inhibited glutamine uptake but glucose, galactose, and fructose did not. In addition to respiratory inhibitors, N-ethylmaleimide inhibited glutamine uptake. Ouabain did not affect glutamine uptake.

Journal Article↗
PubMed1971

Effect of Wilting on Carbohydrates during Incubation of Excised Bean Leaves in the Dark.

Excised bean (Phaseolus vulgaris) leaves were used to compare the changes in various carbohydrates during dark incubation in a wilted and turgid condition. After a rapid (less than 1 hour) wilt, leaves were incubated at a constant water content (75% of original fresh weight).The starch content of the wilted leaves decreased faster than it did in the turgid leaves. This accelerated starch loss was accompanied by an increase in free (alcohol-soluble) sugars, while no similar increase was observed in the turgid leaves. The increase in free sugars in the wilted leaves during accelerated starch loss was sufficient to account for the decreased starch content in wilted leaves compared to turgid leaves. Thus, total carbohydrate decreased at the same rate in both wilted and turgid leaves during dark incubation.The free sugar which accumulated in the wilted leaves was mainly sucrose. There was no increase in sucrose content of turgid leaves during incubation, although there was a rapid loss of starch. Glucose and fructose also increased during incubation, but there was no difference between the wilted and turgid leaves. These results suggest that wilting of detached leaves caused a conversion of starch to sucrose in the dark.

Journal Article↗
PubMed1970

Increase in lytic activity in competent cells of Bacillus subtilis after uptake of deoxyribonucleic acid.

Extractable lytic activity in competent cells of Bacillus subtilis 168 was markedly increased after treatment with homologous or heterologous deoxyribonucleic acid (DNA). This increase was prevented by deoxyribonuclease, and did not occur with B. subtilis W23 or with noncompetent B. subtilis 168 cells, neither of which take up DNA. Although the deoxyribonuclease-sensitive step in DNA uptake was completed within 10 min, the increase in lytic activity did not begin until more than 30 min after the addition of DNA. The increase was prevented by any of several antibiotics. These results are discussed in relation to the mechanisms for the uptake of transforming DNA and the lysis of transfected cells.

Anti-Bacterial Agents↗
PubMed1969

Physical heterogeneity among Bacillus subtilis deoxyribonucleic acid molecules carrying particular genetic markers.

In a Bacillus subtilis deoxyribonucleic acid (DNA) preparation, extracted and purified by the Marmur procedure, the DNA molecules carrying a particular marker are heterogeneous with respect to molecular weight, buoyant density, and thermal stability. This finding constitutes evidence against unique points of breakage during DNA isolation. The variation in buoyant density suggests a local compositional heterogeneity in the chromosomal region of certain markers. The variation in molecular weight provides an explanation for the results of certain transformation experiments that are otherwise poorly understood. An example of such a result is the observation that acridine orange increases the efficiency of differential thermal inactivation of markers. An explanation of this phenomenon is suggested by the demonstration that acridine orange can decrease the natural intramarker heterogeneity in melting behavior.

Acridines↗