Regulation of Carbon Metabolism in Filamentous Fungi

McCullough, W.; Roberts, C. F.; Osmani, Stephen A.; Scrutton, Michael C.

doi:10.1007/978-1-4684-7679-8_9

Cited by 15 publications

(7 citation statements)

References 258 publications

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“…The effect of an increase in demand for NADPH imposed by growth on NO, appears therefore to be confined to three of the NADP-linked dehydrogenases studied here suggesting that these enzymes are responsible for meeting this demand. Our data provide no support for the postulates that either the mannitol cycle (Huh & Gatenbeck, 1978) or a pyruvate-malate cycle (McCullough et al, 1986) might provide a mechanism for generation of NADPH by indirect transfer of reducing equivalents from NADH.…”

Section: Discussioncontrasting

confidence: 93%

“…The presence of the enzymes of the mannitol cycle has been shown in a number of Deuteromycetes (Hult et al, 1980) and evidence suggesting its operation as a mechanism for NADPH generation has been obtained in studies using Alternaria alternata (Hult & Gatenbeck, 1978). However, doubts have been expressed about the operation of this cyclic pathway (McCullough et al, 1986) based on the very unfavourable K , of mannitol dehydrogenase for mannitol (Niehaus & Dilts, 1982) and on the lack of a coordinated (Hult & Gatenbeck, 1978). The enzymes are hexokinase (l), mannitol-1-phosphate dehydrogenase (2), mannitol-l -phosphate phosphatase (3) and NADP-mannitol dehydrogenase (4).…”

Section: Introductionmentioning

confidence: 99%

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NADPH Generation in Aspergillus nidulans: Is the Mannitol Cycle Involved?

Singh

Scrutton²,

Scrutton³

1988

Microbiology

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A cyclic pathway of NADPH generation involving interconversion of mannitol and fructose has been proposed to occur in fungi. In Aspergillus nidulans three enzymes of this proposed mannitol cycle (hexokinase, NADP-mannitol dehydrogenase and mannitol-1-phosphate phosphatase) were shown to be localized exclusively in the cytosol. Two isoenzymes of the fourth enzyme (mannitol-1-phosphate dehydrogenase) were detected and shown to be localized respectively in the mitochondrion and the cytosol. The mitochondrial isoenzyme appeared to be present on the outer face of the inner mitochondrial membrane. No evidence was found for a coordinated change in the maximal activities of the enzymes of the proposed mannitol cycle in extracts prepared from mycelia grown on six different carbon, and three different nitrogen sources nor for any increase in these activities induced by growth on NO;. Studies of this type in which other NADP-linked dehydrogenases were measured showed that for most carbon sources tested growth on NO: increased the maximal activity of NADP-isocitrate dehydrogenase as well as that of glucose-6-phosphate and 6-phosphogluconate dehydrogenases but had little effect on the maximal activity of NADP-malate dehydrogenase (decarboxylating). Our studies provide no support for the operation of the mannitol cycle, or for the proposed role of this cycle in NADPH generation in A . nidulans. INTRODUCTIONProvision of NADPH is a crucial requirement for the continued operation of anabolic pathways such as fatty acid synthesis (Walker & Woodbine, 1976), sterol synthesis (McCorkindale, 1976) and purine synthesis, which utilize this coenzyme as a source of reducing equivalents. NADPH is also used in fungi and other micro-organisms to make oxidized nitrogen sources, e.g. NO;, available for amino acid, purine and pyrimidine synthesis (Lehninger, 1975). In non-photosynthetic micro-organisms it is usually considered that NADPH is generated primarily by the oxidation of glucose 6-phosphate to ri bulose 5-phosphate using glucose-6-phosphate and 6-phosphogluconate dehydrogenases. However, oxidation of isocitrate by NADP-isocitrate dehydrogenase and of malate by NADP-malate dehydrogenase can also contribute to NADPH generation. More recently, Hult & Gatenbeck (1978) proposed a cyclic pathway (Fig. 1) in which interconversion of fructose and mannitol is linked to transfer of reducing equivalents from NADH to NADPH. The presence of the enzymes of the mannitol cycle has been shown in a number of Deuteromycetes (Hult et al., 1980) and evidence suggesting its operation as a mechanism for NADPH generation has been obtained in studies using Alternaria alternata (Hult & Gatenbeck, 1978). However, doubts have been expressed about the operation of this cyclic pathway (McCullough et al., 1986) based on the very unfavourable K , of mannitol dehydrogenase for mannitol (Niehaus & Dilts, 1982) and on the lack of a coordinated ~~~~ ~~~~ t Present address :

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Section: Discussioncontrasting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

NADPH Generation in Aspergillus nidulans: Is the Mannitol Cycle Involved?

Singh

Scrutton²,

Scrutton³

1988

Microbiology

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“…The lack of evidence for the existence of malic enzyme in this organism also supports a completely fermentative mode of lactate formation. Although it has been suggested (McCullough et al, 1986), there is at this time no conclusive evidence for a mitochondrial malate transport system in Rhizopus; therefore, that exchange was not included in this model.…”

Section: Computer Simulation Using Tfluxmentioning

confidence: 85%

Flux Analysis of Glucose Metabolism inRhizopus oryzaefor the Purpose of Increasing Lactate Yields

Longacre

Reimers

Gannon

et al. 1997

Fungal Genetics and Biology

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“…In spite of the extensive reports on enzyme activities in fungi, questions concerning the importance of the mannitol cycle and whether or not it acts as a cycle have never been deWnitively answered (McCullough et al, 1986;Solomon et al, 2005). Since the initial report in 1978, the genes encoding the A. alternata MtDH and MPDH enzymes have not been reported.…”

Section: Introductionmentioning

confidence: 96%