Alkaline phosphatase. II. Conditions affecting determination of total activity in serum.

Results of previous experiments on isolated purified isoenzymes of alkaline phosphatase from humans have been confirmed on sera containing relatively large activities of the different isoenzymes. The most remarkable finding is that activation by N-ethylaminoethanol is much more pronounced, in the case of the intestinal and placental isoenzymes, than is activation by diethanolamine. For several reasons, it is suggested that N-ethylaminoethanol is the buffer of choice, 0.1 mol/liter concentration for routine measurements and 1 mol/liter in those cases where the determination of the intestinal or placental isoenzymes is important. Mg2+ could be omitted because its addition increases the activity only marginally. Normal values for adults with use of 0.1 mol/liter N-ethylaminoethanol are 59 +/- 36 (2 SD) U/liter (n = 126).