Acid hydrolase deficiencies and abnormal glycoproteins in mucolipidosis. 3 (pseudo-Hurler polydystrophy)

Effect of acidotropic amines on the accumulation of newly synthesized membrane and luminal proteins in Chinese-hamster ovary (CHO) cell lysosomes

Lysosomes were isolated by sequential gradient centrifugation [Madden, Wirt & Storrie (1987) Arch. Biochem. Biophys. 257, 27-38] from control or acidotropic-amine-treated Chinese-hamster ovary (CHO) cells. By marker-enzyme analysis, the preparation from chloroquine or NH4Cl-treated cells was about 25-fold enriched for lysosomes compared with the postnuclear supernatant and contained little or no marker activities for the plasma membrane, rough endoplasmic reticulum, Golgi apparatus, mitochondria, cytosol and peroxisomes. The yield of amine-treated lysosomes was about 60% relative to the postnuclear supernatant. Electron microscopy and cytochemistry demonstrated that the amine-treated preparation was highly purified. Cytochemical analyses after a short-term pulse of horseradish peroxidase revealed that endosomal contamination of the lysosomal preparation was less than 1%. Lysosomal polypeptides were biosynthetically labelled with [35S]methionine and identified by SDS/polyacrylamide-gel electrophoresis. As expected, the bulk accumulation of luminal proteins into lysosomes was decreased. The bulk accumulation of membrane proteins was increased by acidotropic amine treatment. There were also several qualitative differences in each lysosomal compartment, with new species observed and other species absent. These data suggest that a low pH is not necessary for the normal accumulation of the bulk of membrane proteins in lysosomes and that membrane trafficking from Golgi apparatus to lysosomes occurs at a high rate in acidotropic-amine-treated CHO cells.

beta-Glucosidase and beta-galactosidase in primary cultures of rat astrocytes: comparison to the brain enzymes

In primary astrocyte cultures beta-glucosidase (EC 3.2.1.21) and beta-galactosidase (EC 3.2.1.23) showed pH optima and Km values identical to rat brain enzymes, using methylumbelliferyl glycosides and labeled gluco- and galactocerebrosides as substrates. The activities of both glycosidases increased in culture up to 3-4 weeks. In rat brain only galactosidase increased; glucosidase activity declined between 12-20 days after birth. The specific activities were two- to sixfold higher in astrocyte cultures than in rat brain. These activities were not due to uptake of enzymes from the growth medium. Secretion of beta-galactosidase, but not beta-glucosidase nor acid phosphatase could be demonstrated. These results support the suggestion of a degradative function for astrocytes in the brain.

Multiple acid phosphatases in avian pectoral muscle--the postmicrosomal supernatant acid phosphatase is elevated in avian dystrophic muscle

There are at least three forms of acid phosphatase in avian pectoralis muscle differing in molecular weight, subcellular location, and response to various substrates and inhibitors. These enzymes are separated by differential sedimentation into postmicrosomal supernatant, lysosomal, and microsomal activities with apparent molecular weights in Triton X-100 of 68,000, 198,000, and 365,000, respectively. All of the enzymes show acid pH optima (pH approximately 5), but the postmicrosomal supernatant form is distinctly different from the other two forms in its resistance to most common phosphatase inhibitors and in its reduced activity against several organic phosphates. Quantitation of these three forms of acid phosphatase in normal and dystrophic avian pectoralis muscle shows that the postmicrosomal supernatant form is significantly elevated in dystrophic muscle; at 33 days ex ovo, 84% of the increased acid phosphatase activity in dystrophic muscle can be attributed to the postmicrosomal supernatant form. The microsomal form is only slightly elevated; the level of the lysosomal form is not altered.

Catalytically defective ganglioside neuraminidase in mucolipidosis IV

Cultured skin fibroblasts from patients with mucolipidosis IV were found to be deficient in neuraminidase activity toward GD1a and GD1b gangliosides radiolabelled in C8 and C7 analogs of their sialic acid residues. Neuraminidase activities toward 4-methylumbelliferyl-N-acetyl-neuraminic acid, neuraminlactose, and radiolabelled neuraminlactitol, fetuin and alpha 1-acid glycoprotein were within the range of normal controls. Fibroblasts from parents of patients with mucolipidosis IV demonstrated intermediate levels of ganglioside neuraminidase activity and normal levels of glycoprotein neuraminidase activity. The residual acidic neuraminidase activity toward GD1a ganglioside in the patients' fibroblasts did not differ from that of controls in its pH optimum and thermostability, but had an abnormal apparent Km which was about 18 times higher than that of the normal enzyme. These findings suggest that mucolipidosis IV is a ganglioside sialidosis due to a catalytically defective ganglioside neuraminidase.

Urinary oligosaccharide excretion in disorders of glycolipid, glycoprotein and glycogen metabolism. A review of screening for differential diagnosis

In recent years great interest has centered around metabolic disorders in which excessive oligosacchariduria is a prominent feature. This review describes the methods of both structural and diagnostic investigations of oligosaccharides in a number of these diseases. Special emphasis has been laid upon simple screening methods which would avail themselves to the clinical chemistry laboratory

Sialidosis type 2 (acid neuraminidase deficiency): clinical and biochemical features of a further case

A further patient with a presumed primary deficiency of sialidase N-acetylneuraminic acid hydrolase EC 3.2.1.18) is described. Clinically the patient falls into the sialidosis type 2 category of the recent classification of Lowden & O'Brien (1979), i.e. he manifests coarse facies, mental retardation and skeletal changes of dysostosis multiplex as well as myoclonus and a cherry-red spot at the macula. Sialidase activity in fibroblasts was 4% of control values using a methylumbelliferone substrate. The father of the patient was found to have 50% activity. Abnormal amounts of sialyloligosaccharides were found in the urine. The electrophoretic mobility of known glycosylated enzymes and proteins was found to be altered (more anodal than usual), but could be corrected by incubation of the cell extracts with bacterial neuraminidase. The relationship of the present patient to the Lowden & O'Brien classification is discussed.

A new variant mucolipidosis: biochemical investigations on two siblings

Biochemical studies are presented on two siblings with some features of Mucolipidosis III, but with distinctive clinical findings. Levels of beta-galatosidase, alpha-mannosidase, beta-glucuronidase, N-acetyl-beta-glucosaminidase and alpha-fucosidase found in serum from these patients ranged from 10 to 10 times higher than normal. The ratio of heat stable to heat labile serum isoenzymes of N-acetyl-beta-glucosaminidase is considerably greater than normal. An extremely low activity of beta-galactosidase was found in fibroblasts cultured from one patient. Levels of the remaining enzymes were in the low normal range. Similarly, beta-galactosidase levels were low in heart, kidney, liver, spleen and lung of one patient who died during the course of the study. Activities of the remaining enzymes were close to normal. No excessive excretion of mucopolysaccharide was noted, however, changes in distribution of several fractions were found. Mucopolysaccharide labeled with radioactive sulfate was degraded by cultured fibroblasts at a normal rate. In addition to clinical differences, the biochemical studies further demonstrate the uniqueness of these patients.

Lysosomal enzymes in medium from cultured skin fibroblasts from normal individuals and patients with lysosomal diseases

The release of acid hydrolases from cultured skin fibroblasts into the cell culture medium was studied in several lysosomal storage disorders (GM1-gangliosidosis, Fabry's disease, Hurler's disease, mannosidosis, and mucolipidosis). The levels of different activities were proportional to time (up to 44 h after medium change) and cell density with the exception of beta-glucosidase, which was not released. Culture medium from the fibroblasts of mucolipidosis patients exhibited higher activity of acid hydrolases than medium from cells of patients with GM1-gangliosidosis, Fabry's disease, Hurler's disease, and mannosidosis. These cells, however, exhibited somewhat higher levels of enzyme activity in their culture medium than control fibroblasts. The total production of acid hydrolases was yet rather similar in fibroblasts from controls and patients. Differential centrifugation showed that the highest specific activity of acid hydrolases was seen, as expected, in the lysosomal fraction, except in fibroblasts from patients with mucolipidosis, where the supernatant exhibited most activity. beta-Glucosidase, however, showed a normal differential centrifugation pattern also in fibroblasts from these patients.