Effects of temperature on measurement of alkaline phosphatase activity

We examined the effects of temperature on the activity and steady-state kinetic properties of alkaline phosphatase (EC 3.1.3.1). Purified isoenzymes from human liver, intestine, and placenta were used, as was human serum, and the enzyme from porcine kidney. Phosphatase activity was estimated by two different assay techniques. For all isoenzymes, apparent Michaelis constants for the substrate 4-nitrophenyl phosphate decreased with increased temperature; Km at 37 degrees C was typically half that determined at 25 degrees C. All enzymes of human origin exhibited similar linear Arrhenius relationships over the range examined, 20-37 degrees C (Ea of 30-36 kJ X mol-1). The porcine kidney enzyme obeyed an Arrhenius relationship that was slightly, but significantly, different from the isoenzymes of human origin. Temperature relationships based upon Arrhenius behavior and individual activity measurements are presented. For human alkaline phosphatases, they differed by no more than 10%.