Phosphofructokinase (PFK) is an important enzyme in virtually all living cells. It performs the committed step in the glycolytic pathway, namely, the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. Glycolysis is a pathway that uses glucose to maintain a steady amount of ATP, the major energy carrier in living cells. Phosphofructokinase is a multisubunit protein. In such proteins, the subunits may behave cooperatively; that is, the activity of one subunit influences the activity of all the other subunits. Proteins that exhibit this behavior are known as allosteric proteins.
What is a 'Variable Cost'. A variable cost is a corporate expense that varies with production output. Variable costs are those costs that vary depending on a company's production volume; they rise as production increases and fall as production decreases. Variable costs differ from fixed costs such as rent, advertising, insurance and office supplies, which tend to remain the same regardless of production output.
Variable costs are expenses that fluctuate proportionally with the quantity of output. Variable costs are directly tied to the activities of producing volume, which rises when those activities increase and falls when activities decrease. This effect can be related to materials, labor, and sales commissions.efinition of Variable Cost. Variable costs are expenses that fluctuate proportionally with the quantity of output. Variable costs are directly tied to the activities of producing volume, which rises when these activities increase and falls when activities decrease.