One of the metabolic enzymes in a cell is phosphofructokinase (PFK-1). In which pathways is it active? (See the Kyoto Encyclopedia of Genes and Genomes.) Phosphorylation controls PFK-1. How does phosphorylated PFK-1 activate and deactivate metabolic pathways? How does this relate to the energy state of the cell? What other molecules regulate PFK-1 activity and how?