Evidence for the activation of 6-phosphofructo-1-kinase by cAMP-dependent protein kinase in Aspergillus niger.

The change from pentose phosphate pathway to glycolysis plays a significant role in the physiology of Aspergillus niger during the induction of citric acid accumulation. Evidence is shown for the importance of 6-phosphofructo-1-kinase in this process since it is activated by phosphorylation. By incubating a purified active form of the enzyme together with commercially available alkaline phosphatase, 6-phosphofructo-1-kinase activity was lost after a certain time suggesting that the enzyme was dephosphorylated. Inactive 6-phosphofructo-1-kinase could be isolated from the cells in the early stage of growth in a high citric acid yielding medium. The enzyme was "in vitro" activated by isolated protein kinase in the presence of cAMP, ATP and Mg2+ ions. Additional evidence for covalent phosphorylation of inactive 6-phosphofructo-1-kinase was obtained by incubating both enzymes together with labelled [gamma-32P]ATP. The activating enzyme was partially purified from A. niger mycelium.