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G LESTER

Publications and source records attributed to G LESTER.

15 recordsLinked to original sources
PubMed1963

Regulation of early reactions in the biosynthesis of tryptophan in Neurospora crassa.

Lester, Gabriel (Reed College, Portland, Ore.). Regulation of early reactions in the biosynthesis of tryptophan in Neurospora crassa. J. Bacteriol. 85:468-475. 1963.-The regulation of the biosynthesis of tryptophan was examined in Neurospora crassa, strain ylo-tryp-la, which accumulates anthranil compounds. The block in this strain appeared to be in the conversion of 1-(o-carboxyphenylamino)-1-deoxyribulose-5-phosphate to indole-3-glycerol phosphate, since the dephosphorylated form of the former compound, the anthranilic ribonucleoside, and the anthranilic acid were found. Cells cultured on levels of l-tryptophan greater than 0.1 mumole per ml were almost devoid of anthranilate-synthesizing activity, whereas cells cultured on low levels of tryptophan (e.g., 0.025 mumole/ml) could produce anthranilate at a rate of 125 mmumoles per mg (dry wt) per hr. A repressive effect was also caused by d-, 5-methyl-dl-, and 6-methyl-dl-tryptophan, but none of these compounds was as effective a repressor as l-tryptophan. Neither 4-methyl-dl-tryptophan, tryptamine, nor indole-3-acetic acid repressed the formation of anthranilate-synthesizing activity. Preformed activity was strongly inhibited by l-tryptophan, and to a lesser extent by 4-, 5-, and 6-methyl-dl-tryptophan; d-tryptophan, tryptamine, or indole-3-acetic acid did not inhibit preformed anthranilate-synthesizing activity. These results are indicative of the operation of repression and feedback-inhibition mechanisms early in the biosynthetic sequence leading to tryptophan. The relation of these results to those concerned with other aspects of tryptophan biosynthesis is discussed.

Glycerophosphates↗
PubMed1962

Permeability and metabolism of lactose in Neurospora crassa.

Lester, G. (Worcester Foundation for Experimental Biology, Shrewsbury, Mass.), D. Azzena, and O. Hechter. Permeability and metabolism of lactose in Neurospora crassa. J. Bacteriol. 84:217-227. 1962.-Germinated conidia of Neurospora crassa suspended in buffer take up lactose, and this uptake can be attributed to the intracellular accumulation and to the metabolism of lactose. The former process predominates initially, and the latter after a few hours of incubation. The accumulation of lactose appears to be mediated by a very specific transport system, which can bring about intracellular concentrations that greatly exceed the external concentration of lactose. Both the influx and efflux of lactose appear to be dependent on metabolic energy, since azide and low temperature inhibit these events. The steroid hormone 11-deoxycorticosterone also reduces the uptake and prevents the accumulation of lactose. The metabolism of lactose was clearly demonstrated, but the pathway(s) of metabolism was not defined. The amount of beta-galactosidase activity extractable from the cells was insufficient to be solely responsible for the initial step in lactose metabolism. The present studies are discussed in relationship to ion permeability and lactose metabolism in N. crassa, and to galactoside permeability in Escherichia coli.

Biological Transport↗
PubMed1961

Repression and inhibition of indole-synthesizing activity in Neurospora crassa.

Lester, Gabriel (Worcester Foundation for Experimental Biology, Shrewsbury, Mass.). Repression and inhibition of indole-synthesizing activity in Neurospora crassa. J. Bacteriol. 82:215-223. 1961.-The possibility of repression and feedback inhibition as regulating mechanisms for the synthesis of tryptophan by Neurospora crassa has been examined in a tryptophan auxotroph which accumulates indole (and indole-glycerol). Indole-synthesizing activity was determined with germinated conidia suspended in medium lacking tryptophan. This activity was almost absent from cells cultured on germination medium containing more than 1.0 mumole l-tryptophan per ml, and increased with decreasing concentrations of l-tryptophan. A similar depression of the formation of indole synthesizing activity was caused by 6-methyl- and d-tryptophan, and less effectively by 5-methyltryptophan; 4-methyltryptophan was slightly stimulatory. Preformed indole synthesizing activity was inhibited by l-tryptophan, 4- and 6-methyltryptophan, and to a lesser extent by 5-methyltryptophan; d-tryptophan had no effect in this respect. The inhibition of preformed activity was partially reversed by anthranilic acid, which is a precursor of indole. However, anthranilic acid did not increase indole synthesis by cells wherein the formation of indole-synthesizing activity had been depressed by culture in the presence of high concentrations of l- or d-tryptophan. These observations indicate that regulation of tryptophan synthesis in N. crassa might result from the action of tryptophan as a repressor and as a feedback inhibitor. The relation of these results to other regulatory systems is discussed.

Indoles↗
PubMed1959

Action of insulin on sugar permeability in rat diaphragm muscle.

Insulin action upon sugar permeability has been examined in rat diaphragm muscle prepared so that the fibers are either intact or cut. In intact preparations, sucrose and mannitol are largely excluded from the intracellular water while D-galactose, D-xylose, and L-xylose equilibrate in a small fraction of the total cell water; the availability of cell water for D-galactose, D-xylose, and L-xylose is increased by insulin. In cut preparations, in which the cell membrane is not intact, all the sugars studied penetrate into the cell, but intracellular water is not uniformly available for subsequent permeation. Sucrose distributes in a volume of about 40 to 45 per cent of the available cell water; D-xylose, D-galactose, L-xylose, and mannitol are distributed in all or most of the cell water, but these sugars diffuse at different rates. In cut preparations insulin increases the rate of equilibration of D-galactose and D-xylose without significant effect on the other sugars studied; insulin also exerts a "directive" influence on glycogen synthesis from glucose, which cannot be explained solely in terms of accelerated sugar penetration. The significance of these observations in elucidating the locus of insulin action is discussed.

Abscess↗