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.
A variable cost is a cost that changes in relation to variations in an activity. In a business, the activity is frequently production volume, with sales volume being another likely triggering event.Thus, the materials used as the components in a product are considered variable costs, because they vary directly with the number of units of product produced.n a business, the activity is frequently production volume, with sales volume being another likely triggering event. Thus, the materials used as the components in a product are considered variable costs, because they vary directly with the number of units of product produced.