Phosphodiesterases in human tissues. II. Decreased hydrolysis of synthetic substrate by tissues from patients with the Niemann-Pick syndrome

Characterization of phosphohydrolase activity in bovine spleen extracts: identification of a bis(p-nitrophenyl)phosphate-hydrolyzing activity (phosphodiesterase IV) which also acts on adenosine triphosphate

Several bovine spleen enzymes with acid pH optima, some of which hydrolyze bis(p-nitrophenyl)phosphate and therefore fit the definition of "phosphodiesterase IV," were partially separated by isoelectric focusing and ion-exchange techniques. The activities were characterized by zymogram analysis with the aid of p-nitrophenyl and 4-methylumbelliferyl phosphate and phosphonate substrates. A number of these enzymes meet the criteria for phosphodiesterase I or other phosphodiesterases. However, the predominant phosphodiesterase I hydrolyzes the bis(p-nitrophenyl)-and 4-methylumbelliferyl phosphates, p-nitrophenyl and 4-methylumbelliferyl phenylphosphonate, and ATP at the beta-gamma bond, but not p-nitrophenyl or 4-methylumbelliferyl 5'-thymidylate (the usual PDE I substrates). These properties, as well as the pH optimum, distinguish the activity from the previously described, alkaline pH optimum PDE I. A second phosphodiesterase hydrolyzes only the phenylphosphonates. Several other activities, less well described, are apparent on zymograms. None of the phosphodiesterases IV was also a phosphodiesterase II (no hydrolysis of 4-methylumbelliferyl 3'-thymidylate).

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.

Purification of sphingomyelinase to apparent homogeneity by using hydrophobic chromatography

Placental sphingomyelinase has been purified to apparent homogeneity by a procedure that makes extensive use of hydrophobic interaction chromatography on sphingosylphosphocholine-CH-, octyl-, hexyl- and Blue-Sepharoses. Enzyme purification is about 10000- 14000-fold over starting extract with excellent yield (usually greater than 28%). Purification of bis-4-methylumbelliferyl phosphate phosphodiesterase activity generally paralleled that of sphingomyelinase during the final stages of the procedure. The enzyme also hydrolysed bis-p-nitrophenyl phosphate, but at a lower rate compared with bis-4-methylumbelliferyl phosphate. A single major protein was observed under non-denaturing conditions. Sphingomyelinase, denatured by reduction and alkylation, is composed of a major polypeptide chain with an apparent molecular weight of 89 100 on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Two minor lower-molecular-weight components were consistently obtained at 47 500 and 30 700. These results were also obtained after maleoylation of the reduced and alkylated sample. The enzyme contains a blocked-N-terminal amino acid. An extensive search for contaminating enzymes revealed the presence of minor amounts of acid phosphatase, which were removed from the final enzyme sample. The highly purified enzyme is stable for several weeks when stored with Triton X-100 at 4 degrees C. The pure enzyme aggregates under denaturing and electrophoretic conditions and special care must be taken to ensure that hydrophobic bonding of the protein is decreased as much as possible. The reproducibility and large scale of this procedure should facilitate further study on the structure and kinetic properties of the enzyme.

A lysosomal enzyme involved in diphosphatidylglycerol degradation

A soluble lysosomal phosphodiesterase in rat liver that hydrolyzes monoacylglycerophosphorylglycerophosphorylglycerol (AGPGPGase) was shown to be distinct from a lysosomal acid phosphodiesterase IV (PDase IV) which catalyzes the hydrolysis of bis(p-nitrophenyl) phosphate. The criteria used to distinguish lysosomal AGPGPGase from PDase IV were: separation on ion exchange celluloses, dissimilar inhibition patterns and different rates of inactivation on concentration. The lysosomal PDase IV activity was competitively inhibited by inorganic phosphate with a Ki value of 0.33 mM phosphate and was inhibited by a number of organophosphoryl compounds including AGPGPG, phosphatidylcholine, phosphatidylinositol, ATP and 4-methylumbelliferylpyrophosphate.

Diagnosis of Niemann-Pick disease using a simple and sensitive fluorimetric assay of sphingomyelinase activity

Phosphodiesterase activity of cultured cells was determined with bis-(4-methylumbelliferyl) phosphate as substrate. In the presence of Triton X-100 an acid component was evident and results indicated that this enzyme was identical with sphingomyelinase. Acid phosphodiesterase activity was specifically inhibited by sphingomyelin. In fibroblasts from patients with Niemann-Pick diseases types A, B and C, acid phosphodiesterase activity was deficient whereas neutral activity was normal. Neutral activity could, however, be removed by acid precipitation or by binding to DEAE-cellulose. Hence a simple and sensitive fluorimetric method is described for the assay of sphingomyelinase activity in the diagnosis of Niemann-Pick disease.

Replacement therapy for inherited enzyme deficiency: liver orthotopic transplantation in Niemann-Pick disease type A

Liver homotransplantation was attempted as replacement therapy in a 2-year-old patient with near total absence of sphingomyelinase activity of Niemann-Pick disease type A. Satisfactory function of the graft was observed until the death of the recipient from respiratory complication 2 years after transplantation. The clinical stigmata of the disease became less severe during the first 6 months after transplantation, with no further improvement thereafter. Sphingomyelinase activity was restored to near normal levels in serum, was present in cerebrospinal fluid and was maintained in the graft at normal or supranormal levels. No accumulation of sphingomyelin was observed in the transplanted organ as evaluated by histopathological and chromatographic studies. These findings support the interest of organ transplantation for long-term enzyme replacement in Niemann-Pick disease type A and similar lysosomal deficiencies.

A practical chromogenic procedure for the detection of homozygotes and heterozygous carriers of Niemann-Pick disease

Niemann-Pick disease is caused by a deficiency of sphingomyelinase in organs and tissues. Determinations of sphingomyelinase activity had required the use of sphingomyelin labeled with radiocarbon or radiohydrogen. These materials are expensive, and their use is restricted to laboratories with radioactive counting facilities. An analogue of sphingomyelin, 2-hexadecanoylamino-4-nitrophenylphosphorylcholine, was synthesized. This substance is hydrolyzed by highly purified sphingomyelinase, and by sphingomyelinease in extracts of human liver tissue, cultured skin fibroblasts, cultured amniotic cells and washed leukocyte preparations. Extracts of tissues and cells from patients with Niemann-Pick disease Type A do not hydrolyze this compound, whereas heterozygotes and patients with Niemann-Pick disease Type C have an intermediate level of hydrolytic activity. Thus, the analogue is a reliable chromogenic reagent for the diagnosis of patients with Niemann-Pick disease and the detection of heterozygous carriers of the Niemann-Pick trait.