Separation and Characterization of Alkaline Phosphatase Isoenzymes from Blood and Other Tissues

Alkaline phosphatases may be contributed to the blood by a number of organs; thus the serum alkaline phosphatase may consist of a mixture of phosphatase isoenzymes. Whether or not these isoenzymes differ other than in their tissues of origin has long been debated, some evidence indicating that they are identical, some that they are different. Attempts to characterize alkaline phosphatase by a study of its properties as it occurs in serum have yielded inconclusive results, because of uncontrolled factors introduced into the experiments by the presence of indeterminate amounts of inhibitors (e.g. amino-acids, bile acids or albumin) and activators (metal cations, amino-acids in low concentrations) in the serum itself. Therefore, if characteristics of tissue phosphatases, such as their Michaelis constants, are to be compared with the corresponding characteristics of the serum enzyme, at least some purification of the latter is necessary. This paper gives a comparison of the Michaelis constants of certain tissue alkaline phosphatases with those of serum alkaline phosphatase from a number of pathological states, the enzymes from both tissues and pathological sera being partially purified by starch-gel electrophoresis. From these comparisons, certain conclusions have been drawn concerning the tissues of origin of serum phosphatase in these diseases.