Stable acid phosphatase: II. Effects of pH and inhibitors

Microdensitometry demonstrated that stable acid phosphatase (SAPhase) in rat and hamster osteoclasts, chondroclasts, and chondrocytes has very similar properties. The differences that were observed suggest that conformational alterations in the enzymes may be responsible for inhibition by some agents such as tartrate. These differences in response to inhibitors depend on the method of embedding as well as on species differences. SAPhase appears to correspond to acid nitrophenyl posphatase, as shown by its pH dependent re-activation, resistance to fluoride inhibition at near-neutral pH, and the inverse effect of pH on inhibition by zinc versus aluminium ions. That proportion of SAPhase resistant to fluoride is an acid phosphatase with activity at near-neutral pH rather than a strict neutral phosphatase. The difference between fluoride sensitive and fluoride resistant SAPhase may relate to the varying association of a single enzyme with cell or lysosomal membranes. The close similarity of acid and neutral SAPhase suggests that both may represent a single enzyme in two forms rather than two distinct enzymes.