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Biomedical subjects

J S O'Brien

Publications and source records attributed to J S O'Brien.

At least 145 records · Page 8Linked to original sources
PubMed1978

Characterization of unusual hexosaminidase A (HEX A) deficient human mutants.

Two families with unusual hexosaminidase A (HEX A) mutations are described. In one, the proband had the Tay-Sachs disease phenotype with considerable HEX A activity. In the second, the proband was phenotypically normal with absent HEX A activity. Activities using ganglioside GM2 as substrate demonstrate markedly reduced activities in the first case and half-normal activities in the second. Pedigree analyses indicate the presence of two different mutations. In the first, the proband appears to be an allelic compound HEX A 2-4 where mutation HEX A 4 leads to a diminution of HEX A activity against GM2 but not for the synthetic substrate, 4MU-beta-D-N-acetyl-glucosaminide, with HEX A 2 being the Tay-Sachs disease (or similar) mutation. In the second family, the proband is an allelic compound HEX A 2-5 where mutation HEX A 5 leads to a diminution of HEX A activity against the synthetic substrate, 4MU-beta-D-N-acetyl-glucosaminide, but not for GM2. The presence of either mutation will lead to false-negative (HEX A 4) or false-positive (HEX A 5) assignments of heterozygosity or homozygosity for GM2 gangliosidosis when synthetic substrates are employed. In both families, DM2 N-acetyl-beta-D-galactosaminidase activity in fibroblasts was an accurate determinant of phenotype.

Adult↗
PubMed1978

Feline GM1 gangliosidosis: characterization of the residual liver acid beta-galactosidase.

The residual liver acid beta-galactosidase (beta-gal) activity from a case of feline GM1 gangliosidosis was partially purified and characterized with respect to its pH optimum, kinetic properties, thermostability, isoelectric point, molecular weight, and antigenicity. In comparison to the normal enzyme, the mutant enzyme had the same pH optima for the three substrates tested, a reduced Km for 4-methylumbelliferyl-beta-gal, elevated Km's for GM1 and asialofetuin (ASF), and increased thermolability. In addition, the mutant beta-gal had a higher isoelectric point, a reduced molecular weight, and appeared to be antigenically different from normal. The results suggest that the mutation in the Birmingham GM1 cat is structural and that the residual enzyme activity is a structurally altered acid beta-gal. The apparent lack of antigenic identity between the mutant and normal enzymes, in contrast to the situation in many human GM1 patients, is most unusual.

Animals↗
PubMed1977

Glycosphingolipid hydrolases: properties and molecular genetics.

This is a review of the properties and molecular genetics of six lysosomal hydrolases: beta-galactosidase, hexosaminidases A and B, alpha-galactosidase, beta-glucosidase and alpha-fucosidase. Each enzyme is discussed with regards to isoenzymes and substrate specificity, subunit structure, genetic relationship of isoenzymes and genetic variants. The molecular genetics of human diseases caused by deficiencies of each enzyme are discussed.

Animals↗
PubMed1977

Purified human liver acid beta-D-galactosidases possessing activity towards G(M1)-ganglioside and lactosylceramide.

Our studies with purified human liver acid beta-D-galactosidases (EC 3.2.1.23) indicate that 4-methylumbelliferyl beta-D-galactosidase and G(M1)-ganglioside beta-D-galactosidase activities are identical with lactosylceramidase II activity. Evidence for this includes co-purification of all enzyme activities by affinity chromatography to yield a single band on polyacrylamide-gel electrophoresis and coincident elution from Sepharose 6B of all three enzyme activities.

Cerebrosides↗
PubMed1977

Ganglioside GM2 N-acetyl-beta-D-galactosaminidase and asialo GM2 (GA2) N-acetyl-beta-D-galactosaminidase; studies in human skin fibroblasts.

Ganglioside GM2 and its asialo-derivative, GA2 were radiolabeled in their N-acetyl-D-galactosaminyl moieties by oxidation with galactose oxidase and reduction with tritiated sodium borohydride. Specific activities of 6 X 10(4) dpm/nmol (GM2) and 1.8 X 10(6) dpm/nmol (GA2) were achieved. About 98% of the label was in N-acetyl-D-galactosamine. Using these substrates, an assay was developed for GM2-N-acetyl-beta-D-galactosaminidase (E.C.3.2.1.30) and GA2-N-acetyl-beta-D-galactosaminidase (E.C.3.2.1.30) activities in human cultured skin fibroblasts. The products of the GM2 cleaving reaction were identified as N-acetylgalactosamine and ganglioside GM3. Both GM2 and GA2 cleaving activities were stimulated about 5-fold by purified sodium taurocholate, and this stimulation was inhibited by neutral detergents, lipids and albumin at low concentrations. Addition of various salts, reducing agents and a protein activator factor from human liver of Li et al. (1973) did not stimulate GM2-N-acetyl-beta-D-galactosaminidase activity beyond that found with sodium taurocholate. Under optimal conditions, control fibroblast supernates cleaved ganglioside GM2 at a rate of 3.7 nmol/mg protein/h compared to 1100 for GA2-N-acetyl-beta-D-galactosaminidase and 4700 for 4-methylumbelliferyl-N-acetyl-beta-D-glucosaminidase. Supernates from two patients with Tay-Sachs disease had markedly reduced activity levels for GM2-N-acetyl-beta-D-galactosaminidase but not for the other two substrates. Supernates from two patients with Sandhoff's disease had reduced activities for all three substrates. A supernate from one patient with juvenile GM2 gangliosidosis cleaved GM2 at a somewhat faster rate than those from Tay-Sachs or Sandhoff's patients. Two healthy adult women with markedly reduced hexosaminidase A activities using 4MU-N-acetyl-beta-D-glucosaminide as substrate had approximately half-normal activities using GM2 as substrate. A patient with the Tay-Sachs phenotype but with a partial deficiency of hexosaminidase A using the 4-MU substrate had a profound deficiency using GM2 as substrate. In such unusual hexosaminidase mutants, assays using GM2 as substrate are better indicators of phenotype than those using synthetic substrates.

Adult↗
PubMed1976

Generalized gangliosidosis: acid beta-galactosidase deficiency with early onset, rapid mental deterioration and minimal bone dysplasia.

This report concerns a 3-month-old girl with rapidly progressive psychomotor retardation, hepatomegaly, vacuolated lymphocytes, minimal bone dysplasia and normal excretion of acid mucopolysaccharides. A deficiency of acid beta-galactosidase was demonstrated in isolated leucocytes and in a liver biopsy. The diagnosis of generalized gangliosidosis due to deficiency of beta-galactosidase was also based on the absence of the enzyme activity from cultured fibroblasts. The diagnosis was confirmed on autopsy at 16 months by typical histology, electron microscopy and biochemistry of the organs. beta-galactosidase deficiency has been demonstrated in various clinical conditions ranging from generalized gangliosidosis with severe mental retardation to clinical pictures resembling Morquio's disease and normal intelligence. The heterogeneity of the clinical manifestations in beta-galactosidase deficiency could be explained by different residual activities of a structurally mutated enzyme towards its various substrates.

Bone Diseases, Developmental↗
PubMed1976

Human leukocyte peroxidase: activity of a soluble and membrane-bound enzyme form in normal persons and patients with neuronal ceroid-lipofuscinosis.

Human leukocytes contain a peroxidase fraction soluble in 0.1 M phosphate buffer and an insoluble peroxidase component with 10--15 times higher specific activity which can be extracted by 0.1 M phosphate buffer + 0.2% Triton X-100 + 0.2% sodium taurocholate and sonication. Both enzyme components have been estimated spectrophotometrically with the substrate hydrogen peroxide (final concentration 1 mM) and the hydrogen donor p-phenylenediamine (final concentration 28-55 mM) within the first 60 sec. The pH-optimum of the soluble and membrane-bound leukocyte peroxidase is at pH 7.0 with a second smaller peak at pH 5.5. Using 0.2 M boric acid/0.05 M sodium borate buffer (pH 7.6) instead of phosphate buffer a 40%-50% increase of enzyme activity can be achieved. In two patients with the juvenile form of neuronal ceroid-lipofuscinosis (type Spielmeyer-Vogt) the activity of soluble leukocyte peroxidase was considerably reduced, in one patient with the late infantile form (type Jansky-Bielschowsky) the activity was just below the normal range, and in two patients with the adult form (type Kuf) activity was normal. In all patients the activity of membrane-bound leukocyte peroxidase was not significantly altered. Only one of four heterozygotes for the juvenile type had deficient values of the soluble enzyme. The variability of the peroxidase findings in patients and carriers with neuronal ceroid-lipofuscinosis make it uncertain whether this represents the primary enzymic defect.

Adolescent↗
PubMed1976

Human saliva peroxidase: microanalytical isoelectric fractionation and properties in normal persons and in cases with neuronal ceroid-lipofuscinosis.

Human saliva contains a high peroxidase activity that can be estimated spectrophotometrically with the hydrogen donor p-phenylenediamine and the substrate hydrogen peroxide from 20 mul of material. The pH optimum of the enzyme with citrate-phosphate buffer is 5.5. After microanalytical isoelectric fractionation 3 main isoenzyme components at pI 8.6, 6.5 and 4.3, and a number of isoenzyme subfractions at pI 9.5, 7.3 and 3.8 are detectable. In 3 patients with the juvenile form of neuronal ceroid-lipofuscinosis (type Spielmeyer-Vogt), in which a deficiency of leukocyte peroxidase had been reported by other authors, both the total activity of saliva peroxidase and the activity of individual isoenzymes were found to be within normal limits. These findings are not consistent with a generalized peroxidase deficiency in this disease.

Ceroid↗
PubMed1976

Isoelectric enzyme patterns of leukocyte peroxidase in normal controls and patients with neuronal ceroid-lipofuscinoses.

Using macro- and microanalytical isoelectric focussing techniques for separation of the soluble leukocytic peroxidase (hydrogen donor: p-phenylenediamine) we found 4 main isoenzyme components with pI at 9.6 (9.0), 7.6 (7.5), 6.2 (6.2) and 4.2 (4.7), which exhibited additional heterogeneities. The isoenzymes of the membrane-bound peroxidase displayed a similar pattern. The isoelectric subfractions of peroxidase in controls and patients with late-infantile (Jansky-Bielschowsky), juvenile (Spielmeyer-Sjögren) and adult (Kufs) types of neuronal ceroid-lipofuscinosis did not reveal any significant differences. Based on these findings, a deficiency of an isoenzyme component cannot be held responsible for producing neuronal ceroid-lipofuscinoses, neither in patients with normal nor in patients with reduced total activity of leukocyte peroxidase.

Adolescent↗
PubMed1976

Spondyloepiphyseal dysplasia, corneal clouding, normal intelligence and acid beta-galactosidase deficiency.

A 14-year-old girl with a unique type of progressive spondyloepiphyseal dysplasia, corneal clouding, and no evidence of neurological abnormality, was found to have a remarkable deficiency of acid beta-galactosidase activity in cultured skin fibroblasts and in leucocyte preparations. In fibroblasts, ganglioside GM1 beta-galactosidase activity averaged 7% of the normal mean while asialofetuin beta-galactosidase and 4-methylumbe lifery-beta-galactosidase averaged 1.4% and 3.5%, respectively. Activities for all three substrates in leucocytes from both her parents were close to 50% of the normal mean indicating that the patient is homozygous for a mutation (or mutations) affecting GM1 beta-galactosidase.

Adolescent↗
PubMed1976

Mucolipidosis II and III: different residual activity of beta-galactosidase in cultured fibroblasts.

A biochemical difference is found between the mucolipidoses II and III which may be correlated with their clinical phenotypes. In homogenates of mass-cultured I-cells from patients with MLII (I-cell disease), the residual specific activity of beta-galactosidase is between 3 and 5 times lower than that in the I-cells from patients with MLIII (pseudopolydystrophy). This difference is confirmed in several coverslip culture experiments where conditions of inoculation, propagation, harvest and enzyme assays are rigidly controlled. MLIII cells also hydrolyse the natural substrates asialofetuin-(H)3-galactoside and GM1- (H)3-galactoside more easily. This observation offers support to the hypothesis that beta-galactosidase may play a role in the physiopathology of these mucolipidoses.

Cytoplasmic Granules↗
PubMed1976

Segregation within a family of two mutant alleles for hexosaminidase A.

A healthy adult female was found to have low levels of hexosaminidase A in serum, leukocytes and fibroblasts when these were assayed with artificial substrates. Fibroblast assay with GM2 ganglioside gave values consistent with a Tay-Sachs heterozygote. Studies of this non-Jewish family revealed evidence for segregation of two mutant alleles for hexosaminidase A.

Adult↗