Turnover of Circulating Enzymes

The homeostasis of circulating enzymes is maintained by an equilibrium between the quantity entering the circulation and the quantity removed per unit of time. Enzymes, like most other circulating substances, are removed at a constant fractional rate with characteristic biological half-lives depending on the enzyme, the isoenzyme, and the species involved. Plasma enzyme activities above normal values may result from increased entry, diminished removal, or both. The composition of a mixture of enzymes or isoenzymes may alter after its entry into circulation because of different removal rates for the various components. These factors should be carefully considered before an "enzyme profile" is regarded as indicative of a disease in a particular organ.