Studies on pyrophosphate diesterase activity in cultured human fibroblasts: a deficiency in Niemann-Pick disease.

Fibroblast phosphodiesterase activity was studied using 4-methylumbelliferyl pyrophosphate diester as substrate. Release of the fluorogen, 4-methylumbelliferone, was found to be dependent on acid phosphatase activity, normally present in excess in crude cell extracts. Phosphodiesterase activity had an acid pH optimum, was deficient in Niemann-Pick disease fibroblasts, and, when assayed in the presence of exogenous acid phosphatase, had an identical electrofocusing profile to that of sphingomyelinase. These findings suggest that 4-methylumbelliferyl pyrophosphate diesterase and acid sphingomyelinase activities are dependent on the same enzyme.