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Biomedical subjects

G Gottschalk

Publications and source records attributed to G Gottschalk.

At least 127 records · Page 7Linked to original sources
PubMed1977

Citrate, a specific substrate for the isolation of Clostridium sphenoides.

With a medium containing citrate as the carbon and energy source, 10 clostridial strains were isolated from various mud samples. Characterization of these strains revealed that they all belonged to the same species, Clostridium sphenoides. Strains of this organism obtained from culture collections were also able to grow citrate, whereas 15 other clostridial species tested were not. Citrate was fermented by C. sphenoides to acetate, ethanol, carbon dioxide, and hydrogen. Experiments with stereospecifically 14C-labeled citrate indicated that citrate lyase was involved in citrate degradation.

Acetates↗
PubMed1977

Energy-dependent inactivation of citrate lyase in Enterobacter aerogenes.

Enterobacter aerogenes was grown in continous culture with ammonia as the growth-limiting substrate, and changes in citrate lyase and citrate synthase activities were monitored after growth shifts from anaerobic growth on citrate to aerobic growth on citrate, aerobic growth on glucose, anaerobic growth on glucose, and anaerobic growth on glucose plus nitrate. Citrate lyase was inactivated during aerobic growth on glucose and during anaerobic growth with glucose plus nitrate. Inactivation did not occur during anaerobic growth on glucose, and as a result of the simultaneous presence of citrate lyase and citrate synthase, growth difficulties were observed. Citrate lyase inactivation consisted of deacetylation of the enzyme. The corresponding deacetylase could not be demonstrated in cell extracts, and it is concluded that, as in a number of other inactivations, electron transport to oxygen or nitrate was required for inactivation.

Aerobiosis↗
PubMed1976

Acetate metabolism in Rhodopseudomonas gelatinosa and several other Rhodospirillaceae.

When Rhodopseudomonas gelatinosa was grown on acetate aerobically in the dark both enzymes of the glyoxylate bypass, isocitrate lyase and malate synthase, could be detected. However, under anaerobic conditions in the light only isocitrate lyase, but not malate synthase, could be found. The reactions, which bypass the malate synthase reaction are those catalyzed by alanine glyoxylate aminotransferase and the enzymes of the serine pathway. Other Rhodospirillaceae were tested for isocitrate lyase and malate synthase activity after growth with acetate; they could be divided into three groups: 1. organisms possessing both enzymes; 2. organisms containing malate synthase only; 3. R. gelatinosa containing only isocitrate lyase when grown anaerobically in the light.

Acetates↗
PubMed1975

Citrate lyase from Streptococcus diacetilactis. Association with its acetylating enzyme.

Citrate lyase (EC 4.1.3.6) was purified 38-fold from cell-free extracts of Streptococcus diacetilactis. The enzyme was homogeneous in analytical ultracentrifugation and polyacrylamide gel electrophoresis. The final enzyme preparation contained acetate: HS-citrate lyase ligase--an acetylating enzyme which converts inactive HS-citrate lyase into enzymatically active acetyl-S-citrate lyase. This enzyme activity was purified 25-fold over the crude extract and seemed to be associated with citrate lyase. Partially purified citrate lyase from Leuconostoc citrovorum contained also its acetylating enzyme. Purified citrate lyases from Klebsiella aerogenes and Rhodopseudomonas gelatinosa were devoid of acetylating enzyme activity. The HS-form of citrate lyase from S. diacetilactis was completely acetylated and hence activated by incubation with ATP and acetate for 25 min at 25 degrees C. The enzyme did not acetylate the HS-lyases from R. gelatinosa and K. aerogenes. In contrast to the citrate lyases from R. gelatinosa and K. aerogenes the enzymes from S. diacetilactis and L. citrovorum showed only a very weak reaction inactivation. It is assumed that this is due to the association of the acetylating enzymes with these lyases.

Acetates↗
PubMed1975

Evidence for cytochrome involvement in fumarate reduction and adenosine 5'-triphosphate synthesis by Bacteroides fragilis grown in the presence of hemin.

Growth of Bacteroides fragilis subsp. fragilis on glucose was very much stimulated by the addition of hemin (2 mg/liter) to the medium. The generation time decreased from 8 to 2 h, and the molar growth yield increased from YM = 17.9 to YM = 47 g (dry weight) of cells per mol of glucose. In the absence of hemin, glucose was fermented to fumarate, lactate, and acetate. The cells did not contain detectable amounts of cytochromes or fumarate reductase. In the presence of hemin, the major products of fermentation were succinate, propionate, and acetate. A b-type cytochrome, possibly a c-type cytochrome, and a very active fumarate reductase were present in the cells. It is concluded from these results that hemin is required by B. fragilis to synthesize a functional fumarate reductase and that the hemin-dependent, enormous increase of the growth yield may be due to adenosine 5'-triphosphate production during reduction of fumarate to succinate.

Acetates↗
PubMed1975

Effect of growth conditions on the activation and inactivation of citrate lyase of Rhodopseudomonas gelatinosa.

Cells of Rhodopseudomonas gelatinosa growing with citrate anaerobically in the light contained citrate lyase only in the acetylated, enzymatically active form of this enzyme. After exhaustion of citrate in the culture medium citrate lyase was deacetylated to yield the inactive sulfhydryl (HS) enzyme. Acetylation of HS-citrate lyase required light, anaerobic conditions and the availability of citrate as substrate. The acetylation reaction already in progress stopped immediately when the culture was placed in the dark. Deacetylation of citrate lyase occurred anaerobically in the light when citrate was exhausted and under aerobic conditions in the presence or absence of citrate. In cells of R. gelatinosa fermenting citrate in the dark neither the acetylating enzyme nor the deacetylating enzyme was active.

Acetylation↗
PubMed1975

Inactivation of citrate lyase from Rhodopseudomonas gelatinosa by a specific deacetylase and inhibition of this inactivation by L-(+1-glutamate.

A previously unrecognized enzyme, citrate lyase deacetylase, has been purified about 140-fold from cell extracts of Rhodopseudomonas gelatinosa. It catalyzed the conversion of enzymatically active acetyl-S-citrate lyase into the inactive HS-form and acetate. The enzyme exhibited an optimal rate of inactivation at pH 8.1. Because of the instability of acetyl-S-citrate lyase at acidic and alkaline pH values, all assays were carried out at pH 7.2, where the spontaneous hydrolysis of the acetyl-S-citrate lyase was negligible and deacetylase showed 70% of the activity at pH 8.1. The apparent Km value for citrate lyase was 10(-7) M at pH 7.2 and 30 C. The activity of the deacetylase was restricted to the citrate lyase from R. gelatinosa. The corresponding lyases from Enterobacter aerogenes (formerly Klebsiella aerogenes) and Streptococcus diacetilactis were not deacetylated; likewise, thioesters such as acetyl-S coenzyme A, acetoacetyl-S coenzyme A, and N-acetyl-S-acetyl-cysteamine were also not hydrolyzed. Citrate lyase deacetylase was present in very small amounts in cells of R. gelatinosa grown with acetate or succinate; it was induced by citrate along with the citrate lyase. L-(+)-Glutamate strongly inhibited the deacetylase. Fifty percent inhibition was obtained at a concentration of 1.4 X 10(-4) L-(+)-glutamate. D-(-)-Glutamate, alpha-ketoglutarate, L-alpha-hydroxyglutarate, L-(-)-proline, and other metabolites were less effective.

Acetates↗