Alkaline phosphatase activity in fetal hind limbs of the mouse mutation brachypodism

A reduction in alkaline phosphatase activity was demonstrated histochemically and biochemically in the hind limbs of brachypod fetal mice. Seventeen‐day brachypod tibias had a 2–3‐fold lower alkaline phosphatase activity than controls of a similar age. In mutant femurs of this age the decrease in activity was as much as 3–4‐fold. Brachypod fibulas never demonstrated enzyme activity in the stages studied. The enzyme from mutant limb tissues showed the same kinetics, thermal stability, and electrophoretic mobility as that from non‐mutant tissues. Embryo extract from 13‐day brachypod mice, reported to inhibit the growth of normal rudiments in vitro, had no effect on the activity of the normal enzyme. It is proposed that the reduction in enzyme activity is a secondary effect related to the disruption and retardation of limb development in the mutant.