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Appl. Environ. Microbiol., Jul 1997, 2844-2849, Vol 63, No. 7
M Gradisnik-Grapulin and M Legisa
A spontaneous rise in intracellular cyclic AMP (cAMP) levels was observed
in the early stages of Aspergillus niger growth under conditions yielding
large amounts of citric acid. The amount of cAMP formed was found to depend
on the initial concentration of sucrose in the medium. Under higher-sucrose
conditions, the cAMP peak appeared earlier and was higher, while in
lower-sucrose media a flattened peak was observed later in fermentation.
Since in media with higher concentrations of sucrose intracellular citric
acid starts to accumulate earlier and more rapidly, cAMP synthesis may be
triggered by intracellular acidification, which is caused by the
dissociation of citric acid. No spontaneous increase in cAMP concentrations
could be detected when the cells were grown in continuously illuminated
cultures, suggesting that A. niger phosphodiesterase (PDE) is
photoregulated. More evidence for the activation of PDE by light was
obtained from morphological studies under light and dark conditions in the
presence of cAMP or N6,O2'-dibutyryl cAMP, and this idea was additionally
supported by experiments in which PDE inhibitors were tested.
Copyright © 1997, American Society for Microbiology
A spontaneous change in the intracellular cyclic AMP level in Aspergillus niger is influenced by the sucrose concentration in the medium and by light
National Institute of Chemistry, Ljubljana, Slovenia.
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