The Formation of Ribulose 1:5-Diphosphate Carboxylase by Growing Cultures of Athiorhodaceae

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SUMMARYThe concentration of ribulose 1,5-diphosphate (RuDP) carboxylase, the enzyme which catalyses the conversion of ribulose 1,5-diphosphate + CO, to 3-phosphoglyceric acid, was partially repressed in some Thiorhodaceae organisms when these were grown on certain organic compounds. Transfer of thiosulphate-grown organisms possessing a high concentration of enzyme into growth medium containing pyruvate caused a rapid decline in carboxylase activity. In the reverse situation, pyruvate-grown organisms preferentially synthesized RuDP carboxylase when transferred to growth medium containing thiosulphate alone. The presence of thiosulphate prevented loss of carboxylase with pyruvate. The incorporation pattern of 14C02 into the ethanol-soluble compounds of organisms metabolizing thiosulphate alone was typical of autotrophic metabolism; most of the CO, was fixed via the reductive pentose cycle. The pattern of incorporation of 14C0, by organisms metabolizing pyruvate was strikingly different in that CO, entered the cell constituents predominantly via a carboxylation leading to a four-carbon product. However, even under the latter conditions, the RuDP carboxylase and the reductive pentose cycle appeared to operate to some extent, since phosphoglycerate was an early product of CO, fixation. Phosphoglycerate was an early product of 14C0, fixation by thiosulphate-grown organisms incubated with a variety of organic substrates, showing that the carboxylase and the reductive pentose cycle could function under these conditions. The addition of thiosulphate increased incorporation of 14C0, into phosphate esters by pyruvate-grown organisms incubated with pyruvate. It is concluded that ribulose diphosphate carboxylase and the reductive pentose cycle function in Thiorhodaceae even when grown on organic substrates ; its quantitative importance was not assessed. The synthesis of the carboxylase was influenced by the growth substrate.

Section: Discussionmentioning

confidence: 99%

“…The method used was slightly modified from that described previously (Lascelles, 1960b). Each tube contained in a final volume of 0.5 ml.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ribulose Diphosphate Carboxylase in Thiorhodaceae

Hurlbert¹,

Lascelles²

1963

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“…It was therefore concluded that this enzyme was ratelimiting for the operation of the EMP under aerobic growth conditions, resulting either in a slow growth rate on fructose or in an increased contribution of the EDP to fructose breakdown. The repression of FBP aldolase under aerobic growth conditions parallels the repression of ribulose-1,5-bisphosphate carboxylase in the same bacterium (Lascelles, 1960); both enzymes are essential for the operation of the Calvin cycle, which is not functional in R. sphaeroides during aerobic growth. In contrast to fructose, glucose was always catabolized via the EDP.…”

Section: Discussionmentioning

confidence: 99%

Influence of Aerobic and Phototrophic Growth Conditions on the Distribution of Glucose and Fructose Carbon into the Entner-Doudoroff and Embden-Meyerhof Pathways in Rhodopseudomonas sphaeroides

Conrad¹,

Schlegel²

1977

~ ~In aerobically and phototrophically growing cells of Rhodopseudomonas sphaeroides, glucose and fructose catabolism were studied by means of enzyme analysis, radiorespirometry and incorporation of specifically-labelled glucose and fructose into spheroidene fractions, into alanine and into valine. Bacteria grown on glucose or fructose possessed all the enzymes necessary for sugar catabolism via the Entner-Doudoroff pathway. Bacteria grown on fructose also contained an inducible . I -phosphofructokinase, indicating that fructose was degraded via fructose I-phosphate. Fructose was catabolized via both the Embden-Meyerhof and Entner-Doudoroff pathways. The contribution of each pathway to fructose breakdown was influenced by the growth conditions : under phototrophic conditions fructose was catabolized predominantly via the Embden-Meyerhof pathway; under aerobic conditions it was catabolized mainly via the Entner-Doudoroff pathway. This change in the major fructose catabolic pathway was paralleled by fructose-I ,6-bisphosphate aldolase activity : the activity was high in phototrophically growing cells and low in aerobically growing cells. Glucose, on the other hand, was catabolized via the Entner-Doudoroff pathway under both phototrophic and aerobic conditions.

“…The fact that added bicarbonate is necessary for growth of photosynthetic bacteria on fatty acids (van Niel, 1944) may be significant although, since only negligibly small amounts of isotope from added NaH14C03 are incorporated b y R. spheroides aerobically metabolizing acetate, CO, is unlikely to act directly as a main precursor of cellular materials under these conditions (Kornberg, to be published). Moreover, the operation of a reductive pentose cycle (Bassham & Calvin, 1957), which could provide a net synthesis of tricarboxylic acid cycle intermediates, cannot account for aerobic growth of the isocitratase-negative organisms on acetate, since ribulose 1 : 5-diphosphate carboxylase is formed only by cultures growing anaerobically in light (Lascelles, 1960).…”

Section: Discussionmentioning

confidence: 99%

The Formation of Isocitratase by the Athiorhodaceae

Kornberg

Lascelles

1960

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SUMMARYIsocitratase, which cleaves isocitrate to glyoxylate and succinate and is a key enzyme in the glyoxylate cycle, is formed by Rhodopseudomonas palustris and R. capsulatus when grown on acetate or butyrate either anaerobically in light or aerobically in the dark. Only traces of the enzyme are present in organisms grown on succinate or malate. In contrast, isocitratase is detectable in traces only in R. spheroides and Rhodospirillum rubrum grown on acetate, butyrate or other substrates. This suggests that the glyoxylate cycle cannot account for net synthesis of cell constituents from acetate or acetate precursors in these latter two organisms.