Reliability of elements and systems in enzymology.

The applications of the elements of reliability to the description of the stability and aging processes of enzymes and polyenzyme systems have been considered. The inactivation of individual enzymes or polyenzyme systems whose activity varies on the molecular level according to the "all-or-nothing" principle is described by an exponential reliability law. Systems of enzymes which are inactivated according to an exponential law have been considered. It has been shown that in the case of enzymes functioning in parallel, the value of the mean time of continuous operation is determined by the most stable enzyme, while in the case of sequentially functioning enzymes, this value is determined by the most labile. Systems whose aging process is related to the accumulation of "latent errors" and whose inactivation is characterized by gradual breakdowns are described by a normal reliability law. Systems with a combination of exponential and normal reliability laws have been considered. The use of a series of rigid quantitative criteria, such as the mean time for continuous functioning has been proposed for characterizing the stability of enzymes and polyenzyme systems. The theoretical points have been illustrated by experimental data on the stability of enzymes with hydrogenase activities, isolated chloroplasts, and cells of microscopic blue-green algae.