AN increasing number of enzymes of intermediary metabolism have been found in serum, and changes in their activities have been correlated with disease processes. We shall discuss some of the factors which appear to regulate enzyme activities and indicate the relatively simple biochemical techniques which are currently employed to enhance the specificity and, thereby, the clinical usefulness of serum-enzyme determinations. We shall confine ourselves to enzymes with a well-defined place in intermediary metabolism and omit others, such as the alkaline phosphatase, which have a long and established record in clinical practice.
Perhaps the most striking property of living matter is its ability to establish and maintain difference in concentration between the cell, extracellular fluid, and subcellular compartments. A comparison of enzyme activities between liver and plasma, illustrated in Table 1, shows the magnitude of this difference. Changes in plasma concentrations of substrates such as glucose, of electrolytes such as sodium
Henley KS, Schmidt E, Schmidt FW. Serum Enzymes. JAMA. 1960;174(8):977-981. doi:10.1001/jama.1960.63030080006007