title: Kinetic of adjustment of enzyme catalytic concentrations in the extracellular space of the man, the dog and the rat. Approach to a quantitative diagnostic enzymology, V. Communication.
abstract: The high degree of constancy of enzyme catalytic activity in the plasma of a given individual is regulated by a complex system of flux equilibria consisting of eight basic processes. Some of these processes are of primarily theoretic importance. Enzymes from all tissues of the body, including the liver, are released via a continuous physiological process into the interstitial space and get into the intravascular space by way of lymphatic transport. The release of enzymes from tissues directly into the intravascular space is of secondary importance as is the exchange of enzyme molecules across capillary membranes from the intravascular to the interstitial space and vice versa. In contrast, enzymes from circulating blood cells are transported directly into the intravascular space. Enzymes are removed from the intravascular space at rates which vary greatly between both enzymes and species. In a review of the literature, half-lives of diagnostically important enzymes in plasma of man, dogs and rats were given and the striking differences in the results for a given enzyme are discussed from a methodological point of view. In a mathematical analysis, data for lymphatic transport of enzymes from dogs and rats (Lindena et al. (1986) this J. 24, 19-33) and of enzyme efflux from in vivo ageing erythrocytes (Lindena et al. (1986) this J. 24, 49-59) into the plasma are related to the elimination rate constants of enzymes from the plasma. The contribution of lymphatically transported enzymes to the basal catalytic activity in plasma (Lindena & Trautschold (1986) this J. 24, 11-18) amounts to 55-80% for lactate dehydrogenase and malate dehydrogenase, 80-90% for adenylate kinase and phosphohexose isomerase, 90-95% for aspartate aminotransferase and aldolase and 99% for creatine kinase. A model of Ca2+ -mediated vesicular transport of enzymes out of ageing erythrocytes is proposed. The importance of lymphatically transported enzymes to total plasma catalytic activity in dogs and rats argues for a similar contribution of lymph transport in man.
mesh_terms: D000818:Animals; D001769:Blood / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D002199:Capillary Permeability; D004796:Clinical Enzyme Tests; D004285:Dogs; D004798:Enzymes / Q000097:blood*; D004905:Erythrocyte Aging; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000201:enzymology / Q000378:metabolism; D005110:Extracellular Space / Q000201:enzymology* / Q000378:metabolism; D006801:Humans; D007424:Intracellular Fluid / Q000201:enzymology / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007527:Isoenzymes / Q000097:blood; D007700:Kinetics; D008208:Lymphatic System / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D011188:Potassium / Q000502:physiology; D051381:Rats
chemical_list: D004798:Enzymes; D007527:Isoenzymes; D011188:Potassium; D002118:Calcium