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At least 379 records · Page 21Linked to original sources
PubMed1984

Partial deficiency of hypoxanthine-guanine phosphoribosyltransferase with reduced affinity for PP-ribose-P in four related males with gout.

A family is described in which four affected males, spanning two generations, have hyperuricemia and gout accompanied by hematuria but are without severe neurologic involvement. The affected males were found to have markedly reduced levels of erythrocytic hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity; these were 5-12% with hypoxanthine and 0.5-3% with guanine as compared to controls. Erythrocytic adenine phosphoribosyltransferase (APRT) was approximately three-fold elevated in the affected individuals. The residual HGPRT activity in affected males enabled characterization of some of the properties of this mutation. The apparent Michaelis constants (km) for both hypoxanthine and guanine were essentially unchanged, whereas the km for PP-ribose-P was approximately 10-20-fold elevated for all four affected males. The enzyme was more sensitive to product inhibition by IMP and GMP than controls, and exhibited greater thermal lability at 65 degrees C than found with control lysates.

Adult↗
PubMed1982

Pentose phosphate pathway mutants of yeast.

A glucose-negative mutant of Saccharomyces cerevisiae lacking 6-phosphogluconate dehydrogenase, the second enzyme of the pentose phosphate pathway, has been obtained by inositol starvation. Suppression of this mutant for growth on glucose takes place by the loss of glucose 6-phosphate dehydrogenase. A lesion in the latter enzyme alone leaves growth practically unaffected. The mutations define the respective structural genes.

Genes↗
PubMed1982

Growth characteristics of Aspergillus nidulans mutans defective in carbohydrate metabolism.

Several mutants aspergillus nidulans defective in carbohydrate metabolism were tested for growth on different carbon sources. D-Galacturonate was found to be a substrate, useful to discriminate between mutants in pyruvate kinase, pyruvate dehydrogenase complex or pyruvate carboxylase. The results of these tests indicate how particular classes of mutants can be obtained and which substrates can be used preferentially for a rapid phenotypical screening of unknown mutants.

Aspergillus nidulans↗
PubMed1983

Regulation of the oxidative phase of the pentose phosphate cycle in Aspergillus oryzae (Ahlburg). I. Induction of glucose-6-phosphate dehydrogenase.

The activity of glucose-6-phosphate dehydrogenase changes when the mycelium is grown on different carbon sources. In the presence of ribose, the activity of the enzyme is approximately 3 times higher than when the mycelium is grow in a medium containing glucose. This increase in the enzyme activity is developed progressively when the concentration of ribose increases from 1% to 6% and it is blocked if cycloheximide is added to the medium. This results suggest an increase in "de novo" synthesis of the enzyme rather than an specific activation of the latent enzyme. Three isoenzymes of glucose-6-phosphate dehydrogenase are isolated from mycelium grown on ribose, whereas only two isoenzymes are isolated from mycelium grown on glucose.

Aspergillus↗
PubMed1976

Ribulose 1,5-diphosphate carboxylase and Cholorobium thiosulfatophilum.

1. Cell-free extracts of the photosynthetic bacterium Cholorobium thiosulfatophilum, strains 8327 and Tassajara, were assayed for ribulose 1,5-diphosphate (RuDP) carboxylase and phosphoribulokinase--the two enzymes peculiar to the reductive pentose phosphate cycle. 2. RuDP carboxylase was consistently absent in strain 8327. The Tassajara strain showed a low RuDP-dependent CO2 fixation activity that was somewhat higher in cells following transatlantic air shipment than in freshly grown cells. The stability and behaviour of this activity in sucrose density gradients were similar to those described by other workers. 3. The radioactive carboxylation products formed in the presence of RuDP by enzyme preparations from the Tassajara strain did not include 3-phosphoglycerate--the known product of the RuDP carboxylase reaction, but instead consisted of the unrelated acids glutamate, aspartate and malate. 4. Phosphoribulokinase was absent in all preparations of the two Chlorobium strains tested. By contrast, phosphoribulokinase as well as RuDP carboxylase were readily demonstrated in preparations from pea chloroplasts and the photosynthetic bacterium Rhodospirillum rubrum. 5. It is concluded that C. thiosulfatophilum appears to lack RuDP carboxylase, phosphoribulokinase, and hence, the reductive pentose phosphate cycle.

Carbon Dioxide↗
PubMed1975

CO2 fixation and its regulation in Anacystis nidulans (Synechococcus).

Anacystis nidulans (Synechococcus) had a minimal doubling time of 5 hrs at 30 degrees C at saturating light intensity and carbon dioxide concentration. Half maximal growth rates in saturating CO2 occured at a light intensity of 0.54 mW per cm2, and there was an apparent threshold intensity of 0.13 mW per cm2 below which no growth occurred. Growth rate in saturating light was dependent on the concentration of CO2+H2CO3 in the medium, rather than on total dissolved CO2; half maximal rates were estimated at 0.1 mM CO2+H2CO3. Under saturating conditions of light and CO2, 14CO2 was fixed primarily into 3-PGA, and subsequently moved into sugar phosphates and amino acids. Incorporation into aspartate was relatively slow. CO2 fixation was strictly light-dependent. The changes in adenylate and pyridine nucleotide pools were followed in light/dark and dark/light transitions. Whereas adenylates relaxed slowly over 15-20 min to the concentrations characteristic of illuminated cells following the abrupt changes induced by darkening, the sharp drop in intracellular NADPH showed little dark recovery although rapid restoration occurred on reillumination. Other pyridine nucleotides showed no changes during these transitions. The nucleotide specificity and Km of partially purfied GAP dehydrogenase suggest a role for this enzyme in the regulation of CO2 fixation.

Adenosine Monophosphate↗
PubMed1976

The capacity of phototrophic sulfur bacterium Thiocapsa roseopersicina for chemosynthesis.

Purple sulfur bacterium Thiocapsa roseopersicina strain BBS requiring vitamin B12 may grow in the dark in media containing no other organic compounds. Under such conditions the cells oxidize sulfide and thiosulfate with the use of O2 and assimilate carbon dioxide. After 10--30s assimilation of NaH14CO3 about 60% of radioactivity is found in phosphorylated compounds characteristic for the reductive pentose phosphate cycle. The possibility of the function of this cycle in the dark in the presence of O2 is confirmed by the capacity of cells grown under such conditions to synthesize ribulose-1,5-diphosphate carboxylase. All this evidence suggests the ability of T. roseopersicina to change from phototrophy to aerobic chemolithoautotrophy.

Aerobiosis↗