A review of enzyme catabolism
Kane, K.K.
Annals of Clinical and Laboratory Science 7(4): 318-324
1977
ISSN/ISBN: 0091-7370 PMID: 900860 Document Number: 115827
Enzyme catabolism is a special category of protein degradation. Protein molecules, once synthesized, appear to break down randomly and not by senescence of individual molecules. Circulating enzymes behave like solutes dissolved in a pool for which input and output rates may vary independently. Enzyme concentrations decline exponentially after transient elevations above steady-state levels. Enzymes are not lost in significant quantities into the urine, feces, bile or saliva. Amylase, which passes freely into the urine, is an exception to this rule. The details of inactivation, degradation and removal of enzymes from circulation are not well understood. Studies on lactate dehydrogenase (LDH) showed that the activity of the enzyme is lost from the circulation more rapidly than the enzyme protein or its fragments are removed. Similar experiments on aspartate transaminase (GOT), alanine transaminase (GPT) and creatine phosphokinase (CK) show these processes to be simultaneous. The RES participates in the clearance process, at least for certain enzymes. Some of the enzyme protein fragments pass into the intestinal tract. Most of this material is further degraded, resorbed and ultimately lost in the urine. Half-life approximations are cited for some enzymes of clinical interest. A clinical study is described in which analysis of the release and clearance of CK after myocardial infarction is used to estimate infarct size.