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M Mitchell

Publications and source records attributed to M Mitchell.

At least 253 records · Page 14Linked to original sources
PubMed1973

Levels of glycogen and trehalose in Mycobacterium smegmatis and the purification and properties of the glycogen synthetase.

The levels of glycogen, free trehalose, and lipid-bound trehalose were compared in Mycobacterium smegmatis grown under various conditions of nitrogen limitation. In a mineral salts medium supplemented with yeast extract and containing fructose as the carbon source, the accumulation of glycogen increased dramatically as the NH(4)Cl content of the medium was lowered. However, levels of free trehalose remained relatively constant. Cells were grown in low nitrogen medium and were then shifted to medium containing high nitrogen. Under these conditions, there was a rapid accumulation of glycogen in low nitrogen, and this glycogen was rapidly depleted when cells were placed in high nitrogen medium. Again the concentration of free trehalose remained fairly constant. However, when cells were grown in low nitrogen medium with [(14)C]fructose and then transferred to high nitrogen medium with unlabeled fructose, the specific radioactivity (counts per minute per micromole) of the free trehalose fell immediately, indicating that it was being synthesized and turned over continually. On the other hand, the specific radioactivity of the glycogen and bound trehalose declined much more slowly, suggesting that these two compounds were not turning over as rapidly or were being synthesized at a much slower rate. Experiments on the incorporation of [(14)C]fructose into glycogen and trehalose indicated that cells in high nitrogen medium synthesized much less glycogen than those in low nitrogen. However, synthesis of both free trehalose and bound trehalose was the same in both cases. The specific enzymatic activities of the glycogen synthetase and the trehalose phosphate synthetase varied somewhat from one growth condition to another, but there was no correlation between enzymatic activity and the amount of glycogen or trehalose, suggesting that changes in glycogen levels were not due to increased synthetic capacity. The glycogen synthetase was purified about 35-fold and its properties were examined. This enzyme was specific for adenosine diphosphate glucose as the glucosyl donor.

Ammonium Sulfate↗
PubMed1973

Trehalose metabolism in germinating spores of Streptomyces hygroscopicus.

Evidence is presented which indicates that utilization of trehalose is an early event in spore germination in Streptomyces hygroscopicus. Early in spore germination and before any increase in cell mass, the activity of trehalase increased more than 15-fold, while the intracellular content of trehalose fell to very low levels. On the other hand, increased activity of the trehalose phosphate synthetase or disappearance of glycogen did not occur until later in germination, during which time cell mass was also increasing.

Disaccharides↗
PubMed1971

Studies on the translocation of noradrenaline-containing vesicles in post-ganglionic sympathetic neurones in vitro. Inhibition of movement by colchicine and vinblastine and evidence for the involvement of axonal microtubules.

1. Methods are presented for studying axonal transport mechanisms in preparations of constricted hypogastric nerve/inferior mesenteric ganglia maintained in vitro for periods up to 48 hr. Under these conditions the ultrastructure of the tissue is excellently preserved.2. The proximo-distal movement of noradrenaline and noradrenaline storage vesicles in the non-myelinated axons of these preparations is inhibited by both colchicine (10 mug/ml.) and vinblastine sulphate (1 mug/ml.) whilst the movement of mitochondria appears to be unaffected.3. Neither colchicine nor vinblastine sulphate depletes accumulated dense-cored vesicles of their stores of noradrenaline.4. These drugs reduce the accumulation of noradrenaline and densecored vesicles against a constriction when they are in contact with the nerve trunks only, and are denied direct access to the nerve cell bodies in the ganglion.5. The only other morphological change that can be attributed to the action of colchicine and vinblastine is a marked reduction in the number of axonal microtubules.6. The experiments provide strong support for the view that the axonal system of microtubules is closely involved in the proximo-distal movement of noradrenaline storage vesicles within noradrenergic neurones. The microtubular system does not appear to be involved in mitochondrial movement.

Animals↗
PubMed1971

Partial purification and properties of a highly specific trehalose phosphate phosphatase from Mycobacterium smegmatis.

A specific trehalose phosphate phosphatase was purified approximately 50-fold from Mycobacterium smegmatis. The enzyme had a pH optimum of about 7.0 and was stimulated by Mg(2+). The optimum concentration of Mg(2+) was about 1.5 x 10(-3)m. Of other divalent cations tested, only Co(2+) showed some activity. The K(m) for trehalose phosphate was found to be about 1.5 x 10(-3)m. The enzyme showed slight activity toward mannose-6-P and fructose-6-P but was inactive on a large number of other phosphorylated compounds. Citrate was a competitive inhibitor of the enzyme both with respect to trehalose phosphate concentration and Mg(2+) concentration. This inhibition appears to be due to chelation of Mg(2+) by this compound. Ethylenediaminetetraacetic acid and NaF were also inhibitors of the enzyme, but these inhibitions were noncompetitive.

Calcium Phosphates↗
PubMed1969

Restoration by Chloramphenicol of Bacteriophage Production in Escherichia coli B Infected with a Ligase-Deficient Amber Mutant.

The addition of chloramphenicol (CM) 5 min after infection of the nonpermissive host Escherichia coli B with the ligase-negative T4 amber, T4 AmH39X, allowed replication of parental deoxyribonucleic acid (DNA) and the production of high-molecular-weight progeny DNA, composed mostly of subunits with a D(2)/D(1) of 0.6. When CM was removed after the accumulation of a large pool of this DNA, most of the infected bacteria were able to produce viable progeny phage, with an average yield of approximately 15 bacteriophage per bacterium. This phenomenon is called CM rescue of the ligase-negative T4 Am. CsCl and sucrose gradient analyses showed both the resulting phage and DNA extracted from them to be similar to the phage and DNA produced on the permissive host. The total transfer of the parental label to progeny phages was as high as 20%. In contrast, in bacteria not treated with CM or in bacteria to which CM was added after phage-coded nucleases had already been synthesized, both parental and progeny (newly synthesized) DNA was composed of very short fragments. Phage which are produced under conditions other than those of CM rescue are dead, light in CsCl, and contain only very short fragments of DNA. Parent-to-progeny transfer in this case is below 1%. When light radio-active parental DNA was used to infect heavy bacteria, DNA replicating in the CM rescue conditions assumed only a hybrid density. After removal of CM and maturation, the parental DNA was incorporated into progeny molecules in fragments constituting approximately 7 to 10% of its mass. This pattern of distribution is essentially what is observed in similar experiments in the permissive host. The role of ligase as an enzyme which compensates for the lethal action of phage-coded nuclease and which is stringently required for the repair of single-stranded nicks is emphasized. The possibility of specific sites for a unique cutting enzyme is discussed in connection with the hypothesis of a circularly permuted assembly of sets.

Journal Article↗