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E Conzelmann

Publications and source records attributed to E Conzelmann.

53 records · Page 3Linked to original sources
PubMed1984

Enzyme-linked immunosorbent assay for the ganglioside GM2-activator protein. Screening of normal human tissues and body fluids, of tissues of GM2 gangliosidosis, and for its subcellular localization.

An enzyme-linked immunosorbent assay was developed for the quantitation of the human activator protein for ganglioside GM2 degradation by beta-N-acetyl-D-hexosaminidase A. With this assay, various tissues and body fluids of normal subjects and of patients with variant forms of GM2 gangliosidosis were screened for their GM2-activator content. The highest content of this protein was found in kidney. Tissues from patients with variant AB of infantile GM2 gangliosidosis contained only low levels (up to 5% of that of normal controls) of cross-reacting material. On subcellular fractionation of normal human skin fibroblasts, the activator was found to co-distribute with the lysosomal marker enzyme beta-hexosaminidase.

Body Fluids↗
PubMed1983

Activator protein for the degradation of globotriaosylceramide by human alpha-galactosidase.

An activator protein which stimulates the degradation of globotriaosylceramide by human hepatic alpha-galactosidase (alpha-D-galactoside galactohydrolase, EC 3.2.1.22) was isolated from human liver and purified some 1300-fold. The purified activator was heat stable up to 95 degrees C, its molecular weight was estimated at 20,000 by gel filtration. Ampholyte displacement chromatography resolved the activating factor into two fractions with isoelectric points at pH 4.6 and pH 4.8, respectively, with otherwise identical properties. The protein did not stimulate the hydrolysis of the water-soluble 4-methylumbelliferyl-alpha-galactoside.

Chymotrypsin↗
PubMed1983

Activating proteins for ganglioside GM2 degradation by beta-hexosaminidase isoenzymes in tissue extracts from different species.

The existence of activator proteins that stimulate hydrolysis of ganglioside GM2 by beta-hexosaminidase was demonstrated in kidney extracts from four species (rat, mouse, cattle and pig). The extent to which these preparations, as well as their human counterpart, promote ganglioside GM2 catabolism by autologous and heterologous hexosaminidase isoenzymes was compared. It was found that these activators can replace each other functionally, although the animal activator proteins do not cross-react immunochemically with an antiserum against the human protein. All preparations examined catalysed the transfer of ganglioside GM2 between liposomal membranes, indicating that the animal activator proteins act by a mechanism similar to the human GM2 activator.

Animals↗
PubMed1983

Ganglioside GM2 N-acetyl-beta-D-galactosaminidase activity in cultured fibroblasts of late-infantile and adult GM2 gangliosidosis patients and of healthy probands with low hexosaminidase level.

A sensitive assay was developed to assess the ability of extracts from cultured fibroblasts to catabolize ganglioside GM2, in the presence of the natural activator protein but without detergents. This method, which permitted the reliable determination of residual activities as low as 0.1% of normal controls, was then used to measure ganglioside GM2 hydrolase activities in fibroblasts from several hexosaminidase variants. The residual activities thus determined correlated well with the clinical status of the respective proband: infantile Tay-Sachs (0.1% of normal controls), late-infantile (0.5%), and adult GM2 gangliosidoses (2%-4%) and healthy probands with "low hexosaminidase" (11% and 20%). In contrast, beta-hexosaminidase A levels as measured with the synthetic substrate 4-MU-GlcNAc could not be relied on for diagnostic purposes (the late-infantile patient studied retained 80% of the activity of controls).

Cells, Cultured↗
PubMed1982

Complexing of glycolipids and their transfer between membranes by the activator protein for degradation of lysosomal ganglioside GM2.

The lysosomal degradation of ganglioside GM2 by hexosaminidase A depends on the presence of the specific activator protein which mediates the interaction between micellar or membrane-bound ganglioside and water-soluble hydrolase. The mechanism and the glycolipid specificity of this activator were studied in more detail. 1. It could be shown with three different techniques (isoelectric focusing, centrifugation and electrophoresis) that the activator protein extracts glycolipid monomers from micelles or liposomes to give water-soluble complexes with a stoichiometry of 1 mol of glycolipid/mol of activator protein. Liposome-bound ganglioside GM2 is considerably more stable against extraction and degradation than micellar ganglioside. 2. In the absence of enzyme the activator acts in vitro as glycolipid transfer protein, transporting glycolipids from donor to acceptor membranes. 3. The activator protein is rather specific for ganglioside GM2. Other glycolipids (GM3 GM1, GD1a and GA2) form less stable complexes with the activator and are transferred at a slower rate (except for ganglioside GM1) than ganglioside GM2.

Electrophoresis, Polyacrylamide Gel↗
PubMed1982

Lysosomal enzyme precursors in human fibroblasts. Activation of cathepsin D precursor in vitro and activity of beta-hexosaminidase A precursor towards ganglioside GM2.

Precursors of cathepsin D and beta-hexosaminidase were isolated from secretions of human fibroblasts and their activity was studied with natural substrates. The immunoprecipitated precursor of cathepsin D, Mr 53000, was inactive with radioactive hemoglobin as substrate. At pH 3.8-4.2 an activation of the precursor took place, which was correlated by a reduction in size to Mr 51500. The observed cleavage of cathepsin D precursor in vitro resembles the autocatalytic activation of pepsinogen. The precursor of beta-hexosaminidase A is able to cleave the natural substrate GM2 ganglioside. This reaction, like that of the mature enzyme, depends on the presence of a protein activator, which interacts with the substrate and the enzyme.

Cathepsin D↗
PubMed1982

Model for the interaction of membrane-bound substrates and enzymes. Hydrolysis of ganglioside GD1a by sialidase of neuronal membranes isolated from calf brain.

Microsomes and synaptosomes isolated from calf brain contain a sialidase which cleaves ganglioside substrates. The hydrolysis of [3H]ganglioside GD1a by the membrane-bound enzyme has been studied under various conditions. The reaction rate decreased with increasing ionic strength in the incubation mixture, and was progressively enhanced by increasing concentrations of the primary alcohols n-pentanol to n-octanol. This stimulation correlates quantitatively with an increase in membrane 'fluidity' caused by these alcohols as measured by fluorescence depolarization employing 1,6-diphenyl-1,3,5-hexatriene as probe. The dependence of the reaction rate on the amount of enzyme in the incubation mixture was linear only with water-soluble substrates but not with the lipophilic ganglioside substrate. Evidence is presented that lipophilic substrate and enzyme interact mainly within the plane of the membrane presumably by lateral diffusion. Taking this into consideration Michaelis-Menten theory was modified accordingly. As predicted, apparent Km values increased linearly with the amount of membrane-bound enzyme added and decreased with the concentration of n-hexanol in the incubation mixture. In the presence of varying n-hexanol concentrations the apparent Km-value decreased with increasing membrane 'fluidity', as measured by fluorescence depolarization of 1,6-diphenyl-1,3,5-hexatriene. On the other hand, as expected, V values were not affected by membrane 'fluidity' and increased linearly with the amount of membrane protein.

Alcohols↗
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↗
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

AB variant of infantile GM2 gangliosidosis: deficiency of a factor necessary for stimulation of hexosaminidase A-catalyzed degradation of ganglioside GM2 and glycolipid GA2.

Human kidney extracts heated to 60 degrees and devoid of hexosaminidase activity (2-acetamido-2-deoxy-beta-D-glucoside acetamidodeoxyglucohydrolase EC 3.2.1.30) stimulate more than 20-fold the hexosaminidase A-catalyzed degradation of ganglioside GM2 and of glycolipid GA2, the neuronal storage compounds of GM2 gangliosidosis. The stimulating factor of this extract, which is labile at temperatures above 60 degrees, is also present in kidney extracts from patients with infantile GM2 gangliosidosis having a deficiency of hexosaminidase A (Tay-Sachs disease, variant B) and a deficiency of hexosaminidases A and B (variant 0). Evidence is presented that this factor is defective in the AB-variant of infantile GM2 gangliosidosis which is characterized by an accumulation of glycolipids GM2 and GA2 despite the fact that the degrading enzymes, hexosaminidases A and B, retain normal activity levels. Thus, variant AB is an example of a fatal lipid storage disease that is caused not by a defect of a degrading enzyme but rather by a defective factor necessary for the interaction of lipid substrates and the water-soluble hydrolase.

Enzyme Activation↗
PubMed1978

Purification, biochemical and immunological characterisation of hexosaminidase A from variant AB of infantile GM2 gangliosidosis.

Variant AB of infantile GM2 gangliosidosis is a fatal disease leading invariably to death within the first few years of life, due to the excessive storage of the glycolipids GM2 and GA2 which occurs in the nervous tissue of the patient. Unlike other variants of this hereditary disease, where a deficiency of hexosaminidase A, the ganglioside-GM2-degrading enzyme, could be demonstrated, the variant AB is characterized by a normal or even elevated level of this enzyme. To examine the possibility of a mutant hexosaminidase A, well capable of hydrolyzing the fluorogenic synthetic substrates but unable to attack the ganglioside, the enzyme was isolated from a patients tissue and characterized biochemically and immunologically in comparison with an enzyme preparation from normal control tissue. No differences between hexosaminidase A from normal and variant AB tissue could be detected indicating that the defect involved in this disease is not at the genetic level of production of either alpha or beta chains of hexosaminidase A.

Child, Preschool↗
PubMedDate not supplied

[Adrenoleukodystrophy in a pair of siblings].

The diagnosis of adrenoleukodystrophy (ALD) in two brothers was confirmed by the analysis of long-chain fatty acids in cultured skin fibroblasts. The 23 year old brother was treated for Addison's disease at the age of 7 years. His first symptoms of ALD developed at the age of 22. These were lack of concentration and compulsive disorder. The younger brother was noted to show behavioural changes and a decreased performance at school at age 9. The disease then progressed rapidly. Variability and diagnostic procedures are discussed in this report.

Addison Disease↗