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Biomedical subjects

E C Lin

Publications and source records attributed to E C Lin.

At least 163 records · Page 9Linked to original sources
PubMed1971

Anaerobic L- -glycerophosphate dehydrogenase of Escherichia coli: its genetic locus and its physiological role.

In mutant cells of Escherichia coli missing the particulate l-alpha-glycerophosphate (l-alpha-GP) dehydrogenase necessary for aerobic growth on glycerol or l-alphaGP, a soluble, flavine-dependent l-alpha-GP dehydrogenase supports normal anaerobic growth rates on either of the two substrates with fumarate or nitrate as exogenous hydrogen acceptor. In an experiment in which glycerol served as the carbon source and nitrate as the acceptor, the growth of such a mutant was arrested upon the admission of air, whereas the growth of wild-type cells continued smoothly. Mutant cells lacking the soluble l-alpha-GP dehydrogenase, but possessing the particulate enzyme, can grow at normal rates aerobically on glycerol and l-alpha-GP or anaerobically on these compounds with nitrate, but not fumarate, as the hydrogen acceptor. Double mutants lacking both of the dehydrogenases fail to show significant growth on either glycerol or l-alpha-GP under any condition. Mutations affecting the anaerobic dehydrogenase (glpA locus) are situated at about minute 43 of the Taylor map, just clockwise beyond glpT, and show cotransduction with purF (1.5%), glpT (91%), and nalA (50%). The anaerobic dehydrogenase is a member of the glp regulon as judged by its inducibility by l-alpha-GP and by its constitutive formation in strains of glpR(c) genotype. The level of the anaerobic dehydrogenase is about the same in cells grown either aerobically or anaerobically with nitrate serving as a terminal hydrogen acceptor. With fumarate as terminal acceptor, the level is elevated several fold.

Aerobiosis↗
PubMed1970

Glycerol kinase, the pacemaker for the dissimilation of glycerol in Escherichia coli.

The activity of glycerol kinase is rate-limiting in the metabolism of glycerol by cells of Escherichia coli. A mutant strain producing a glycerol kinase resistant to inhibition by fructose-1,6-diphosphate grows faster than its wild-type parent on glycerol as the sole source of carbon and energy. The amount of intracellular fructose-1,6-diphosphate was determined for wild-type cells growing exponentially on glycerol. The water content of such cells was also determined, allowing calculation of the intracellular concentration of fructose-1,6-diphosphate. This value, 1.7 mm, is adequate to exert substantial inhibition on the wild-type glycerol kinase. The desensitization of glycerol kinase to feedback inhibition also enhances the power of glycerol to exert catabolite repression, both on the enzymes of the glycerol system itself and on those of the lactose system. However, desensitization of glycerol kinase alone does not eliminate the phenomenon of diauxic growth in a glucose-glycerol medium. Biphasic growth in such a medium is abolished if the altered enzyme is produced constitutively. The constitutive production of the mutant kinase at high levels, however, renders the cells vulnerable to glycerol. Thus, when the cells have been grown on a carbon source with a low power for catabolite repression, e.g., succinate, sudden exposure to glycerol leads to overconsumption of the nutrient and cell death.

Carbon Isotopes↗
PubMed1969

Ferrous-activated nicotinamide adenine dinucleotide-linked dehydrogenase from a mutant of Escherichia coli capable of growth on 1, 2-propanediol.

A nicotinamide adenine dinucleotide-linked dehydrogenase has been partially purified from a mutant of Escherichia coli K-12 able to grow on l-1,2-propanediol as carbon and energy source. This enzyme catalyzes the dehydrogenation at carbon 1 of l-1,2-propanediol, glycerol, 1,3-propanediol, ethylene glycol, and ethyl alcohol. The purified protein requires added ferrous or managanous ions. The V(max) and the apparent K(m) for a given substrate vary with the particular metal used.

Centrifugation, Density Gradient↗
PubMed1968

Mutants of Aerobacter aerogenes capable of utilizing xylitol as a novel carbon.

Wild-type Aerobacter aerogenes 1033 is unable to utilize xylitol. A succession of mutants was isolated capable of growth on this compound (0.2%) at progressively faster rates. Whereas the ability to utilize xylitol was achieved in the first-stage mutant (X1) by constitutive production of ribitol dehydrogenase (for which xylitol is a substrate but not an inducer), the basis for enhanced utilization of xylitol in the second-stage mutant (X2) was an alteration of ribitol dehydrogenase. This enzyme was purified from the various mutants. The apparent K(m) for xylitol was 0.12 m with X2 enzyme and 0.29 m with X1 enzyme. The X2 enzyme was also less heat stable and, at 0.05 m substrate concentration, had a higher ratio of activity with xylitol compared to ribitol than did the X1 enzyme. The third mutant (X3), with an even faster growth rate on xylitol, produced a ribitol dehydrogenase indistinguishable physically or kinetically from that of X2. However, X3 produced constitutively an active transport system which accepts xylitol. The usual function of this system is apparently for the transport of d-arabitol since the latter is not only a substrate but also an inducer of the transport system in parental strains of X3. The sequence of mutations described herein illustrates how genes belonging to different metabolic systems can be mobilized to serve a new biochemical pathway.

Alcohol Oxidoreductases↗
PubMed1967

Replacement of a phosphoenolpyruvate-dependent phosphotransferase by a nicotinamide adenine dinucleotide-linked dehydrogenase for the utilization of mannitol.

Mannitol is dissimilated by Aerobacter aerogenes via an inducible pathway initiated by a phosphotransferase system dependent upon phosphoenolpyruvate as the phosphoryl donor. A mutational block in this pathway can be suppressed either at the phenotypic level by induction of d-arabitol dehydrogenase, an enzyme fortuitously capable of converting mannitol to fructose, or genotypically by a constitutive mutation in the d-arabitol system.

Enterobacter↗
PubMed1966

Feedback inhibition of glycerol kinase, a catabolic enzyme in Escherichia coli.

Fructose-1 ,6-diphosphate is a feedback inhibitor of the catabolic enzyme, glycerol kinase, in Escherichia coli. A mutant was isolated which produced a desensitized enzyme. Glucose was no longer as effective in preventing the utilization of exogenous glycerol by cells which synthesized constitutively such an altered enzyme, even though the usual degree of catabolite repression still operated.

Enzymes↗
PubMed1966

Chromosomal location of the structural gene for glycerol kinase in Escherichia coli.

Cozzarelli, N. R. (Harvard Medical School, Boston, Mass.), and E. C. C. Lin. Chromosomal location of the structural gene for glycerol kinase in Escherichia coli. J. Bacteriol. 91:1763-1766. 1966.-A glycerol kinase mutant site has been mapped by transduction and sexual conjugation. Three-factor crosses with the two procedures yielded the following gene order: arginine-1-methionine-1-glycerol kinase-isoleucine, valine-16. An additional 13 independent glycerol kinase mutant sites mapped in the same region. Since some of the mutants were able to produce a protein serologically indistinguishable from the wild-type enzyme, it is concluded that the region mapped represents the structural gene for the kinase.

Chromosome Mapping↗
PubMed1965

Growth stasis by accumulated L-alpha-glycerophosphate in Escherichia coli.

Cozzarelli, N. R. (Harvard Medical School, Boston, Mass.), J. P. Koch, S. Hayashi, and E. C. C. Lin. Growth stasis by accumulated l-alpha-glycerophosphate in Escherichia coli. J. Bacteriol. 90:1325-1329.1965.-Cells of Escherichia coli K-12 can grow on either glycerol or l-alpha-glycerophosphate as the sole source of carbon and energy. The first step in the dissimilation of glycerol requires a kinase, and the initial process of utilization of l-alpha-glycerophosphate involves an active transport system. In either case, intracellular l-alpha-glycerophosphate is an intermediate whose further metabolism depends upon a dehydrogenase. When this enzyme is lost by mutation, the cells not only fail to grow on glycerol or l-alpha-glycerophosphate, but are subject to growth inhibition in the presence of either compound. Resistance to inhibition by glycerol can be achieved by the loss of glycerol kinase. Such cells are still susceptible to growth inhibition by l-alpha-glycerophosphate. Similarly, in dehydrogenase-deficient cells, immunity to exogenous l-alpha-glycerophosphate can be achieved by genetic blocking of the active transport system. Such cells are still sensitive to free glycerol in the growth medium. Reversal of inhibition by glycerol or l-alpha-glycerophosphate in cells lacking the dehydrogenase can also be brought about by the addition of glucose. Glucose achieves this effect without recourse to catabolite repression. Our results suggest that growth stasis associated with the over-accumulation of l-alpha-glycerophosphate is due to interference with other cellular processes by competition with physiological substrates rather than to depletion of cellular stores of adenosine triphosphate or inorganic phosphate.

Escherichia coli↗