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K Sandhoff

Publications and source records attributed to K Sandhoff.

At least 235 records · Page 13Linked to original sources
PubMed1981

Cerebroside sulfatase activator deficiency induced metachromatic leukodystrophy.

Two siblings of consanguineous parents had presented with a variety of findings indicative of juvenile metachromatic leukodystrophy (MLD). However, instead of the expected profound deficiency of arylsulfatase A (ARS A), their enzyme levels were about half-normal, and enzyme from fibroblasts had properties identical with the properties of enzyme from normal fibroblasts. Nevertheless, the hydrolysis of cerebroside sulfate by growing fibroblasts was markedly attenuated. Supplementation of the fibroblasts with cerebroside sulfatase activator normalized the response in the loading test. These results imply that the fibroblasts, and by extension the patients, are deficient in activator. Although the defective catabolism of cerebroside sulfate and the clinical manifestations in these patients mimic MLD, the molecular basis is distinct from the classical forms of the disorder.

Cerebroside-Sulfatase↗
PubMed1980

Assay of ganglioside GM2-N-acetyl-beta-D-galactosaminidase activity in human fibroblasts employing the natural activator protein--diagnosis of variant forms of GM2 gangliosidosis.

The physiological activator protein for the degradation of ganglioside GM2 by hexosaminidase A has been employed to assess the capability of cultured human fibroblast extracts to catalyze this ganglioside. This method permits a more reliable diagnosis of the different variants of GM2 gangliosidoses than the methods hitherto used. These either rely on artificial substrates or, when natural substrates are used, on detergents. Our method avoids a number of possible sources of error introduced by the unphysiological detergents, such as alteration of the isoenzymes' substrate specificity or inactivation of the enzymes. The range of application of the new method is discussed.

Cells, Cultured↗
PubMed1980

The specificity of human N-acetyl-beta-D-hexosaminidases towards glycosphincolipids is determined by an activator protein.

It has been very difficult to correlate, on the basis of in vitro measurements of substrate specificities, the glycosphingolipid storage patterns observed in different variants of infantile GM2 gangliosidosis with the hexosaminidase (hex) isoenzyme deficiencies underlying these diseases. However, the in vitro enzyme assays included detergents, which greatly enhanced the enzymic degradation of lipids by breaking down the large lipid micelles that cannot otherwise be attacked by the hydrolases. In vivo, the role of detergent is taken over by water-soluble, low molecular weight proteins, so-called activators, which bind the lipid monomers, thus solubilizing them. It can be shown that the activator protein for the enzymic degradation of ganglioside GM2 has a very strong preference for hex A over hex B; it also acts on glycolipid GA2 and, to a lesser extent, on kidney globoside. This isoenzyme specificity is much less prominent or even reversed when detergents are used to solubilize the substrates. The substrate specificities of hex A and hex B measured in the presence of sufficient amounts of the activator protein most probably reflect the conditions occurring in vivo. They can explain the lipid storage patterns observed in different variants of infantile GM2 gangliosidosis, especially the accumulation of ganglioside GM2 in variant B (where hex B is still present) and the reduced storage of GA2 in the same variant as compared to variants O and AB. The physiological significance of the activator protein is demonstrated in variant AB in which the activator is deficient, resulting in an accumulation of glycolipids GM2 and GA2.

Enzyme Activation↗
PubMed1980

[Lipid-protein interactions: mechanisms of enzymatic glycolipid catabolism and their genetic restrictive escapes].

Investigations of the genetic basis of ganglioside catabolism have led to the characterisation of two types of lipid-enzyme interaction: a) Breakdown of membrane-bound glycolipids as far as catalysed by membrane-bound enzymes is regulated by the membrane itself. b) The degradation of micelle-forming glycolipids by water-soluble lysosomal enzymes is facilitated by cofactors known as activator proteins. A genetic defect in an activator protein can be just as fatal as the lack of the enzyme itself.

Animals↗
PubMed1980

Wolman's disease: clinical, biochemical and ultrastructural studies in an unusual case without striking adrenal calcification.

A case of Wolman's disease is described in a German infant who died at the age of 4 months. Hepatosplenomegaly, abdominal distention, gastrointestinal symptoms, dyserythropoietic changes in the bone marrow, but not adrenal calcification on X-ray were present. Stored lipid material could be demonstrated in liver, spleen, intestine, adrenals, thymus, kidneys, blood cells, but not in the central nervous system. Cholesterylesters and triglycerides were markedly increased in liver and spleen. Lysosomal acid lipase was found to be decreased in leucocytes and liver to less than 10% of normal, when measured with synthetic and natural substrates.

Adrenal Glands↗
PubMed1979

Biochemistry and genetics of gangliosidoses.

The gangliosidoses comprise an-ever increasing number of biochemically and phenotypically variant diseases. In most of them an autosomal recessive inherited deficiency of a lysosomal hydrolase results in the fatal accumulation of glucolipids (predominantly in the nervous tissue) and of oligosaccharides. The structure, substrate specificity, immunological properties of and genetic studies on the relevant glycosidases, ganglioside GM1 beta-galactosidase and beta-hexosaminidase isoenzymes, are reviewed in this paper. Contrary to general expectation, only a poor correlation is observed between the severity of the disease and residual activity of the defective enzyme when measured with synthetic or natural substrates in the presence of detergents. For the understanding of variant diseases and for their pre- and postnatal diagnosis, the necessity of studying the substrate specificity of normal and mutated enzymes under conditions similar to the in vivo situation, e.g., with natural substrates in the presence of appropriate activator proteins, is stressed. The possibility that detergents may have adverse affects on the substrate specificity of the enzymes is discussed for the beta-hexosaminidases. The significance of activator proteins for the proper interaction of lipid substrates and water-soluble hydrolases is illustrated by the fatal glycolipid storage resulting from an activator protein deficiency in the AB variant of GM2-gangliosidosis. Recent somatic complementation studies have revealed the existence of a presumably post-translational modification factor necessary for the expression of ganglioside GM1 beta-galactosidase activity. This factor is deficient in a group of variants of GM1-glangliosidosis. Among the possible reasons for the variability of enzyme activity levels in heterozygotes and patients, allelic mutations, formation of hybrid enzymes, and the existence of patients as compound heterozygotes are discussed. All these may result in the production of mutant enzymes with an altered specificity for a variety of natural substrates.

Adolescent↗
PubMed1979

Purification and characterization of an activator protein for the degradation of glycolipids GM2 and GA2 by hexosaminidase A.

The activator protein for the degradation of glycolipids GM2 and GA2 by hexosaminidase A was purified some 2 500-fold from normal human kidney. It has a molecular weight of approximately 25 000 is heat-stable up to 60 degrees C, possesses an isoelectric point of pH 4.8 and is digestible by proteases. Enzymic degradation of the lipid substrates in the presence of this activator proceeds optimally at pH 4.2. The mode of action of the activator was also studied: the protein most probably complexes lipid molecules and presents them to the enzyme which otherwise cannot attack the aggregates formed by the lipids in aqueous solution. The hydrolysis of water-soluble synthetic substrates is not affected by the activator protein. The activator is highly specific for hexosaminidase A: hydrolysis of glycolipids GA2 and GM2 by the hexosaminidase B isoenzyme is almost not enhanced by this protein. The isoenzymes' lipid substrate specificity measured in the presence of the activator is entirely different from that obtained with detergents and can satisfactorily account for the lipid storage pattern observed in patients with variant forms of infantile GM2- gangliosidosis.

Binding Sites↗
PubMed1978

Prenatal diagnosis of Tay-Sachs disease in cell-free amniotic fluid.

The diagnosis of 6 known Tay-Sachs cases was confirmed by isoelectric focusing of the cell-free amniotic fluid. The presence of an additional--hitherto unknown--heatstable, acid hexosaminidase X in normal and pathological amniotic fluids must be taken into account especially when the heat denaturation method of detecting Tay-Sachs disease is applied. Hexosaminidase X shows some properties similar to those of hexosaminidase B.

Amniotic Fluid↗
PubMed1978

Studies on bovine brain membrane-bound neuraminidase (sialidase).

1) Lipophilic ganglioside GD1a (IV3NeuAc, II3NeuAc-GgOse4-Cer) is taken up by the cell membranes and hydrolyzed faster by membrane-bound neuraminidase than are water soluble substrates of the enzyme. 2) The enzymic breakdown of ganglioside GD1a is enhanced by general anesthetics whereas the degradation of the hydrophilic substrate sialyllactitol is reduced by these same agents. 3) General anesthetics lower the microviscosity of membranes as indicated by studies of fluorescence depolarisation with the indicator 1,6-diphenylhexatrien. Decreased microviscosity can result in a higher lateral diffusion of ganglioside GD1a, increasing its interaction with membrane-bound neuraminidase. 4) In vitro studies indicate that the activity of membrane-bound neuraminidase on gangliosides of brain membranes is regulated by the viscosity of these membranes and their monosialoganglioside content.

Animals↗
PubMed1978

Membrane-bound neuraminidase from calf brain: regulation of oligosialoganglioside degradation by membrane fluidity and membrane components.

The degradation of lipophilic ganglioside GD1a and hydrophilic sialyllactitol by membrane-bound neuraminidase (EC 3.2.1.18) from calf brain has been studied at substrate concentrations of 0.1 mM. Ganglioside GD1a taken up by cell membranes is hydrolyzed faster membrane-bound neuraminidase than are water-soluble substrates of the enzyme, sialyllactitol and des-GD1a. Availability and enzymic breakdown of the disialoganglioside are enhanced by general anesthetics such as N2O or halothane whereas the degradation of the hydrophilic substrate silayllactitol is not affected or even is decreased by these agents. General anesthetics lower the microviscosity of membranes as indicated by studies of fluorescence depolarization with the indicator 1,6-diphenylhexatriene. Increased fluidity can result in higher lateral diffusion of ganglioside GD1a, thus increasing its chances of presentation to, and interaction with, membrane-bound neuraminidase. Lipophilic derivatives of the disialoganglioside, gangliosides GM1 and GM2 and gangliotriaosylceramide GA2, are strong inhibitors of the ganglioside degradation whereas water-soluble derivatives des-GM1, des-GM2, N-acetylneuraminic acid, and sialyllactose are not. A model is presented that suggests that the activity of membrane-bound neuraminidase on gangliosides of brain membranes is regulated by the viscosity of these membranes and their monosialoganglioside content.

Anesthesia, General↗