[The economy of protein maintenance in the living cell]

On the economy of proteins in living cells Each synthesized protein of a cell is of certain metabolic advantage, but at the same time also a load on the energy and material metabolism. "Costs" as well as "profit" vary with the amount of protein formed, and the optimal amount would maximize the profitability, i.e. profit minus cost. The paper deals with the special case of an enzyme necessary for substrate uptake, which is therefore of advantage for the energy budget of the cell, whose biosynthesis, however, drains this budget at the same time. This example allows a mathematical formulation of the concept of profitability and shows, with the help of a basic kinetic model that indeed an optimum exists. Its existence follows from the rather general fact that the advantage of an enzyme reaches a saturation value, if its amount increases, while the "cost factor" continues to increase in a linear manner.