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Biomedical subjects

B Geiger

Publications and source records attributed to B Geiger.

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

Localization of acetylcholine receptor in excitable membrane from the electric organ of Torpedo: Evidence for exposure of receptor antigenic sites on both sides of the membrane.

Nicotinic acetylcholine receptor was localized in a receptor-rich membrane preparation from the electric organ of Torpedo californica by applying an immunoferritin technique. The membrane preparation was incubated with (Fab')2 fragments derived from specific rabbit antibodies against the purified acetylcholine receptor and subsequently with ferritin-conjugated goat antiserum to rabbit immunoglobulin. More than 50% of the vesicles were found to be labeled with ferritin while the rest remained unlabeled. Ferritin labeling on both sides of the membrane was evident in open membrane vesicles, whereas in closed vescles the labeling was confined to the outer surface due to the inability of the tracer to penetrate the membrane. These data suggest that antigenic sites of the receptor molecule are exposed on both sides of the excitable membrane, and that acetylcholine receptor may be a transmembrane protein.

Animals↗
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↗
PubMed1978

Hexosaminidase A in amniotic fluid of Tay-Sachs fetuses.

Hexosaminidase A is present in relatively low concentrations in cell-free amniotic fluids from pregnancies with Tay-Sachs fetuses. This isoenzyme was determined by an immunological procedure, radial immunodiffusion, by which hexosaminidase A can be directly and specifically detected, even in the presence of excess amounts of hexosaminidase B. No hexosaminidase A could be detected by the same procedure in Tay-Sachs fetal tissues, implying that this isoenzyme in the amniotic fluid originates from the mother.

Amniotic Fluid↗
PubMed1978

The mode of interaction with macrophages of two ordered synthetic polypeptides which differ in their thymus dependency.

The mode of interaction with macrophages of two ordered synthetic polypeptides (Tyr-Tyr-Glu-Glu)-poly(DLAla)--poly(Lys), (T-T-G-G)-A--L, and (Tyr-Glu-Tyr-Glu)-poly(DLAla)--poly(Lys), (T-G-T-G)-A--L, which differ in their requirements for T-B cell co-operation in the process of antibody production, was compared. The binding of the two radiolabelled antigens to the surface of peritoneal adherent cells, their uptake by the cells and the rate of their degradation were investigated. Macrophages were found to be capable of degrading both poly-peptides with the same efficiency. (T-G-T-G)-A--L, the antigen which is less T-dependent, was bound to macrophage surfaces more readily than (T-T-G-G)-A--L, the T-dependent antigen, however, its uptake by the cells was found to be lower. Thus, (T-G-T-G)-A--L remains for a longer period in the form of a membrane bound polyvalent antigen.

Animals↗
PubMed1977

Stabilization of human beta-D-N-acetylhexosaminidase A towards proteolytic inactivation by coupling it to poly(N-vinylpyrrolidone).

Human hexosaminidase A was covalently bound to soluble poly(N-vinylpyrrolidone), and the effect of this binding on the enzyme inactivation by various procedures was investigated. Whereas the polymer-bound hexosaminidase underwent inactivation to the same extent as the free enzyme, when exposed to heat or acidic pH, the conjugation to polymer appeared to protect the enzyme towards proteolysis. Thus, the polymer-bound enzyme exhibited considerably higher resistance to treatment of both pronase and macrophage cathepsins. The clearance rate from rabbit blood, of the polymer-bound enzyme (expressed as enzyme activity), was shown to be significantly slower than that of the free enzyme.

Drug Stability↗
PubMed1977

Immunochemical determination of ganglioside GM2, by inhibition of complement-dependent liposome lysis.

Immunochemical quantitative determination of a lipid antigen, ganglioside GM2, has been developed, based on the inhibition of the immune lysis of liposomes containing the antigen in their lipid bilayer. It has been shown that the full expression of the antigenicity of the competing lipid requires its dispersion in accessory lipids. The assay of inhibition of liposome lysis can be used also for the establishment of the antigenic similarity of structurally related lipid antigens.

Animals↗
PubMed1977

Immunochemical and biochemical investigation of hexosaminidase S.

Hexosaminidase S (HEX S), the residual isozyme found in tissues and body fluids of children with the O variant of GM2 gangliosidosis, was purified from tissues of variant individuals and biochemically and immunochemically characterized. This enzyme has an apparent molecular weight of 103,000 with an isoelectric point of 4.2, is heat labile to the same extent as HEX A, and loses most of its activity following heating for 30 min at 50 degrees C. HEX S reacts immunologically with the antisera against either HEX A or B, but the reaction is considerably stronger with the anti-A serum or with antibody preparations which react exclusively with the A isozyme. Results obtained by a radioimmunoassay using the various antisera indicated that there is no antigenically cross reacting material which lacks enzymatic activity in the variant tissues. These findings are in accord with a suggested molecular structure of two subunits, each composed of two alpha chains (alpha2 alpha2) for HEX S; it also implies that alpha and beta chains have some structural similarity which is manifested in antigenic cross-reactivity.

Antibodies↗
PubMed1976

Chemical characterization and subunit structure of human N-acetylhexosaminidases A and B.

Human hexosaminidases A and B were purified from placentae, using two stages of affinity chromatography, to a high degree of purity. Each enzyme was purified 5000-6000-fold, and isolated in 25-40% yield. Enzyme preparations appeared homogeneous in the analytical ultracentrifuge and by acrylamide gel electrophoresis. Hexosaminidase A contained 1.65 residues of sialic acid per molecule, whereas no sialic acid was present in hexosaminidase B. The molecular weights of the A and B isozymes as determined by gel filtration and sedimentation equilibrium are 100 000 and 108 000, respectively. In 5 M guanidine-HCl each of the enzymes yielded a 50 000-dalton species, which can further be dissociated into 25 000-dalton polypeptide chains by reduction and alkylation. The hexosaminidase B yielded one type of polypeptide chain, denoted beta, whereas the product from hexosaminidase A could be separated by ion-exchange chromatography into two species of chains, denoted alpha and beta, in equal amounts. The amino acid compositions of the separated alpha and beta chains were determined, and were found to correlate well with those of the intact enzymes. These findings enable the construction of a plausible model for the molecular structure of both enzymes. According to this model hexosaminidase A is composed of two subunits alpha2 and beta2, in which the two polypeptide chains are linked by a disulfide bridge. The structure of hexosaminidase B is, in parallel, beta2beta2. The suggested model is discussed in view of the accumulated information about the interrelationships between hexosaminidase A and B and the genetic metabolic disorders with which they are involved.

Amino Acids↗
PubMed1976

Low levels of beta hexosaminidase A in healthy individuals with apparent deficiency of this enzyme.

Appreciable beta hexosaminidase A (hex A) activity has been detected in cultured skin fibroblasts and melanoma tissue from healthy individuals previously reported as having deficiency of hex A activity indistinguishable from that of patients with Tay-Sachs disease (TSD). Identification and quantitation of hex A, amounting to 3.5%-6.9% of total beta hexosaminidase activity, has been obtained by cellulose acetate gel electrophoresis, DEAE-cellulose ion-exchange chromatography, radial immunodiffusion, and radioimmunoassay. Previous family studies suggested that these individuals may be compound heterozygotes for the common mutant TSD gene and a rare (allelic) mutant gene. Thus, the postulated rate mutant gene appears to code for the expression of low amounts of hex A. Heterozygotes for the rare mutant may be indistinguishable from heterozygotes for the common TSD mutant. However, direct visualization and quantitation of hex A by the methods described may prevent false-positive prenatal diagnosis of TSD in fetuses having the incomplete hex A deficiency of the type described in the four healthy individuals.

Cells, Cultured↗
PubMed1975

Specific determination of N-acetyl-beta-D-hexosaminidase isozymes A and B by radioimmunoassay and radial immunodiffusion.

The two major isozymes of N-acetylhexosaminidase, namely hexosaminidases A and B were quantitatively determined in tissues and biological fluids of both normal individuals and Tay-Sachs patients. The determination was carried out by two sensitive immunoassays:radial immunodiffusion, using chromogenic substrate, and radioimmunoassay, which were developed in this study. For this purpose [corrected] we used either a cross-reactive antiserum which reacts to a similar extent with both isozymes, or an antiserum reacting exclusively with hexosaminidase A (obtained by selective immunoadsorption). This enabled the quantitisation of the two isozymes separately, or in the presence of each other, in purified enzyme preparations or in tissue homogenates, affording a direct positive determination of hexosaminidase A. The results demonstrated that normal tissues contain the two isozymes in comparable amounts, whereas tissues of Tay-Sachs patients lack hexosaminidase A or any material which carries the A-specific antigenic determinants. The possible applications of these assays and their potential use in diagnosis are discussed.

Acetylglucosaminidase↗