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 signif icant 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 phos phorylation. By incubating a purified active form of the enzyme togeth er with commercially available alkaline phosphatase, 6-phosphofructo-1 -kinase activity was lost after a certain time suggesting that the enz yme was dephosphorylated. Inactive 6-phosphofructo-1-kinase could be i solated from the cells in the early stage of growth in a high citric a cid yielding medium. The enzyme was 'in vitro' activated by isolated p rotein kinase in the presence of cAMP, ATP and Mg2+ ions. Additional e vidence for covalent phosphorylation of inactive 6-phosphofructo-1-kin ase was obtained by incubating both enzymes together with labelled [ga mma-P-32]ATP. The activating enzyme was partially purified from A. nig er mycelium.