Biosynthesis of acid alpha-glucosidase in late-onset forms of glycogenosis type II (Pompe's disease)

Cultured human skin fibroblasts from control persons and from patients with the generalized and late-onset forms of Pompe's disease were labelled with radioactive leucine and the incorporation of radioactivity into acid alpha-glucosidase and cathepsin D was analysed by immunoprecipitation, gel electrophoresis and fluorography. When the labelling was carried out for 6-12 h in the presence of NH4Cl, the labelling of secreted alpha-glucosidase relative to that of secreted cathepsin D in fibroblasts from patients with the late-onset form of Pompe's disease was less than 15% of that in fibroblasts from control persons. However, when the fibroblasts were labelled for less than 1 h, the relative rate of incorporation of radioactivity into acid alpha-glucosidase was rather similar in the two types of fibroblasts. In fibroblasts from patients with the generalized form of Pompe's disease no incorporation of radioactivity into acid alpha-glucosidase could be detected.     

Subcellular distribution of acid alpha-glucosidase in fibroblasts and of antigenically cross-reactive material in Pompe's disease fibroblasts

From fibroblasts of two cases of Pompe's disease (acid alpha-glucosidase deficiency), one of the childhood type (RH-SF-1) and one of the adult type (RH-SF-2), and normal fibroblasts, antigenically cross-reactive material and acid alpha-glucosidase were immunoprecipitated and analysed by immunoelectrotransfer blotting. The acid alpha-glucosidase and antigenically cross-reactive material (which reacts with antibody raised against normal acid alpha-glucosidase) revealed a precursor form of molecular weight 97,000 and two major components of 79,000 and 76,000. When monensin was added to the fibroblast culture, the two major components of normal acid alpha-glucosidase were decreased, whereas the large molecular weight precursor was increased. On the other hand, the 97,000 molecular weight component of cross-reactive material in the Pompe's fibroblasts (RH-SF-1 and RH-SF-2) was only slightly increased on monensin treatment. The fibroblasts were pulse-chase labelled with [2-H3] mannose and 32Pi. The cross-reactive material and acid alpha-glucosidase were precipitated with anti acid alpha-glucosidase antibody, and after sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), fluorography was performed. The radiolabel of 3H in the cross-reactive material of RH-SF-1 and -2 was weak, and 32P in the cross-reactive material of both fibroblasts was very weak when compared with those of the acid alpha-glucosidase. The radiolabel of 32P in the cross-reactive material of RH-SF-1 was extremely weak. Immunofluorescence histochemistry revealed a granular localization of acid alpha-glucosidase in the normal fibroblast cytoplasm, and a diffuse distribution of cross-reactive material in the cytoplasm of RH-SF-1 and -2. Immuno-electron microscopic examinations showed a normal acid alpha-glucosidase localization on the inner side of the lysosomal membrane and also diffusely in the lysosome; when treated with monensin, it was present on the trans part of the Golgi apparatus. Antigenically cross-reactive material, however, was found in the cytoplasm and endoplasmic reticulum. Some lysosomal localization was observed sporadically. Even after monensin treatment, it was not demonstrated on the Golgi apparatus.     

Species-specific antibodies of Tetrahymena acid alpha-glucosidase.

1. Tetrahymena acid alpha-glucosidases A and B were purified from T. pyriformis W and T. thermophila 399, respectively. The acid alpha-glucosidases A and B were different in immunological properties and thermostability. 2. The acid alpha-glucosidases A and B reflected specific distribution between T. pyriformis and T. thermophila. 3. Type A and B of taurolipid showed a species-specific distribution pattern between T. pyriformis and T. thermophila.     

Use of different hapten-protein conjugates immobilized on nitrocellulose to screen monoclonal antibodies to abscisic acid

The dot-immunobinding method for screening antibodies to proteins on sheets of nitrocellulose has been modified to allow monoclonal antibodies (McAb) to the hapten abscisic acid (ABA) to be screened. Several methods for conjugating ABA to proteins using new bifunctional coupling reagents, specific for hapten keto groups, are described. Hybridomas secreting McAb with a defined specificity for the hapten can be identified by screening supernatants against the carrier protein and other hapten-protein conjugates with different conjugation bridges or modified hapten structure. Inhibition of binding to conjugates by free hapten is used to determine the relative avidity of the McAb for free and bound hapten. All of these tests could be done with no more than about 50 microliter of antibody solution. Dot immunobinding is a useful alternative to radioimmunoassay for screening McAb to haptens.     

Genetic heterogeneity in acid alpha-glucosidase deficiency.

Several clinical forms of acid alpha-glucosidase deficiency have been described. Our study was planned to identify differences at the molecular level in acid alpha-glucosidase deficiency. Of nine fibroblast strains derived from patients with the infantile form of the disease, eight were crossreacting material (CRM)-negative and one CRM-positive. This was demonstrated by both agar immunodiffusion and immunotitration. No difference in apparent enzymatic activity was observed between CRM-negative and CRM-positive infantile acid alpha-glucosidase deficiency fibroblasts. In two fibroblast strains with the adult form of acid alpha-glucosidase deficiency, rocket immunoelectrophoresis demonstrated a reduction in the amount of enzyme protein, which was directly proportional to the reduction in enzyme activity. In another fibroblast strain obtained from a patient with the adult form of the disease, the activity was within the range of the infantile form and no CRM could be identified. Fibroblasts with phenotype 2 of acid alpha-glucosidase, considered a normal variant, showed a reduction both in the amount of enzyme protein and in the ability of the enzyme to cleave glycogen. However, the catalytic activity for maltose was normal. The findings demonstrate extensive genetic heterogeneity in acid alpha-glucosidase deficiency. Molecular differences were identified both between the clinical forms of the disease and within the infantile and the adult forms of acid alpha-glucosidase deficiency. It remains unknown whether or not the enzyme deficiency in homozygotes for isozyme 2 of acid alpha-glucosidase will be sufficient to cause glycogen accumulation and lead to the development of muscular dystrophy-like disease later in life.     

On the origin of alpha-glucosidase in human urine

The recent findings that alpha-glucosidase from human kidney was identical with one component (F1) of the alpha-glucosidases found in human urine suggested the idea that this enzyme might originate in the kidneys. The present study was performed to test this idea by immunological methods. Urine alpha-glucosidase F1 was isolated in the electrophoretically homogeneous state, and the antibody prepared in rabbits was purified by affinity chromatography after the antisera were fractionally precipitated with ammonium sulfate and chromatographed on diethylamino ethyl (DEAE)-cellulose. The staining of human kidney tissue sections was performed by the indirect method, using alpha-glucosidase F1 antibody and fluorescein-conjugated anti-rabbit immunoglobulin goat sera. The proximal convoluted portion (proximal tubules) with brush border and Henle's loops (late proximal) were stained clearly. Preincubation of intact antibody with purified antigen prevented specific staining of the proximal convoluted portion and Henle's loops. In contrast, all other tissues of kidney were stained less positively or negatively. These results indicate that alpha-glucosidase F1 originates in the kidney, and that glucosidase is specifically localized in the proximal convoluted portion and Henle's loops.     

Hematopoietic contribution to skeletal muscle regeneration in acid alpha-glucosidase knockout mice.

Recent studies have shown that cells from bone marrow (BM) can give rise to differentiated skeletal muscle fibers. However, the mechanisms and identities of the cell types involved remain unknown. We performed BM transplantation in acid alpha-glucosidase (GAA) knockout mice, a model of glycogen storage disease type II, and our observations suggested that the BM cells contribute to skeletal muscle fiber formation. Furthermore, we showed that most CD45+:Sca1+ cells have a donor character in regenerating muscle of recipient mice. Based on these findings, CD45+:Sca1+ cells were sorted from regenerating muscles. The cell number was increased with granulocyte colony-stimulating factor after cardiotoxin injury, and the cells were transplanted directly into the tibialis anterior (TA) muscles of GAA knockout mice. Sections of the TA muscles stained with anti-laminin-alpha2 antibody showed that the number of CD45+:Sca1+ cells contributing to muscle fiber formation and glycogen levels were decreased in transplanted muscles. Our results indicated that hematopoietic stem cells, such as CD45+:Sca1+ cells, are involved in skeletal muscle regeneration.     

Some properties of human liver acid alpha-glucosidase.

1. Albumin activates human liver acid alpha-glucosidase (alpha-D-glucoside hydrolase, EC 3.2.1.20). From the Arrhenius plot, pH-dependence and Lineweaver-Burk plots it can be concluded that this activation is not only due to stabilisation of the enzyme, but also influences the enzymatic activity. It is proposed that for optimal functioning human liver acid alpha-glucosidase needs a protein environment. 2. Glycogen has a competitive inhibitory effect on the hydrolysis of 4-methylumbelliferyl-alpha-D-glucopyranoside, in contrast to maltose which exhibits a non-competitive type of inhibition. It is concluded that two catalytic sites exist, one for glycogen and one for maltose, while both sites influence each other. With glycogen as substrate a break in the Arrhenius plot is found. This is not the case when maltose is used as substrate. 3. The effect of antibody raised against human liver acid alpha-glucosidase on the activity of human liver acid alpha-glucosidase is studied. No corss-reacting material could be demonstrated in the liver of a patient with glycogen storage disease Type II (M. Pompe, acid alpha-glucosidase deficiency).     

Affinity chromatography of yeast alpha-glucosidase using ligand-mediated chromatography on immobilized phenylboronic acids.

The synthesis of 3-nitro-4-(6-aminohexylamido)phenylboronic acid is described. The properties of two novel forms of immobilized phenylboronate agarose adsorbents [m-aminophenylboronic acid-Matrex Gel and 3-nitro-4-(6-aminohexylamido)phenylboronic acid-Sepharose CL-6B] were investigated. Both gels bind and selectively retard the glycoprotein alpha-glucosidase from yeast. The retardation is affected by following parameters: (i) pH, (ii) presence of sugar, (iii) concentration of sugar and (iv) buffer species (especially triethanolamine). Five sugars were studied, namely sorbitol, fructose, ribose, glucose and maltose. The concentration of sugar required to produce significant retardation increased in the above order, whereas the ability of sugar to form a complex with boron decreases in the same order. These effects were observed with crude as well as pure enzyme. Since alpha-glucosidase is a glycoprotein, it is proposed that this protein is mainly bound to these immobilized phenylboronates via sugar (glyco) residues. Displacement of the enzyme from the column is effected by the sugar in the buffer (or in a preincubation mixture). However, the marked pH-dependence (this retardation effect could only be observed at pH 7.4) suggests that these results are not due solely to hydrophobic or ionic mechanisms and are more complex than simple sugar-phenylboronic acid interactions.     

Use of monoclonal antibodies to separate the enantiomers of abscisic acid

The resolution of racemates often requires difficult and time consuming purification procedures. McAb technology allows the production of specific antibodies in quantities suitable for the preparation of matrices for large scale affinity purification. Here we report the rapid separation of abscisic acid (ABA) enantiomers by affinity chromatography using McAb. This method appears to be far superior to previously published separations based on crystallization, chromatography, and affinity purification with conventional antisera. The approach here described will be particularly attractive in a wide variety of similar situations.     

Temporal relation of antigenaemia and loss of antibodies to core antigens to development of clinical disease in HIV infection.

A total of 276 sequential serum samples from 34 men with antibodies to the human immunodeficiency virus (HIV) followed up for two to seven years were analysed for HIV antigen and antibodies to the viral core and envelope proteins. Results were correlated with clinical outcome and CD4 T lymphocyte count. Both antigenaemia and the disappearance of antibodies to the core protein were associated with development of the acquired immune deficiency syndrome (AIDS) or AIDS related complex and depletion of CD4 cells. Thus AIDS or AIDS related complex developed in eight out of 16 patients with antigenaemia compared with one out of 18 patients without antigenaemia. Low counts of CD4 cells (less than 0.5 X 10(9)/l) were found in 14 of the 16 patients with antigenaemia and five of the 18 without antigenaemia. Nine patients seroconverted to HIV during the study; two of these developed antigenaemia 14 and 16 months after the estimated time of seroconversion. These results show that the late stages of HIV infection are characterised by increased production of antigen and a decrease in antibodies directed against the core protein. Antigenaemia indicates a poor prognosis; and as the antigen test is simple to do and interpret, it may therefore be useful for selecting patients for antiviral treatment.     

Immobilization of alpha-glucosidase in chitosan coated polygalacturonic acid

Crude alpha-glucosidase from Baker's yeast was immobilized in polygalacturonic acid beads and coated with chitosan. Chemical and physical characterization were performed by using p-nitrophenyl-alpha-D-glucopyranoside (pNPG) as an artificial substrate. Operation, thermal, pH, and strorage stabilities of the free and immobilized enzyme were also examined. The stabilities of immobilized enzyme were found to be better than that of the free enzyme. Furthermore, the hydrolysis rate of the chitosan coated alpha-glucosidase polygalacturonic acid beads were studied. In conclusion, the enzyme beads appear to have good characteristics and offer the prospect that this system may find application in enzyme immobilization, in addition to controlled drug release studies.     

Use of enzyme-labeled antibodies to detect Salmonella in foods.

An indirect enzyme-labeled antibody technique (ELAT), in which Salmonella typhimurium was used as a model, was developed as a method to detect Salmonella in food samples. A cellulose-acetate membrane filter, the matrix for detection, was placed on a membrane-filter base and overlaid with a multiwelled lucite template. Mixed broth enrichment cultures were dispensed in the template wells, and cells were spotted onto the membrane via suction. After fixation, the membranes were immersed in rabbit anti-S. typhimurium flagella antibody, washed, immersed in goat anti-rabbit antibody conjugated to peroxidase, and washed. Exposure of membranes to the substrates 3,3'-diaminobenzidine or benzidine resulted in development of brown or blue macroscopic reaction products, respectively, on spots containing S. typhimurium. ELAT results agreed with those of enrichment serology and cultural procedures on three food products containing known levels of S. typhimurium. Because of the magnification effect of the enzyme-substrate reaction, fewer cells were needed for detection than with enrichment serology, thereby reducing the total analysis time. The ability to test 14 or more samples simultaneously on a 47-mm membrane filter would facilitate screening large number of samples. Pending the development of a pure H antisera pool for the common Salmonella serotypes free from O antibodies, the ELAT demonstrated potential as a Salmonella detection methodology.     

Use of enzyme-labeled antibodies to detect Salmonella in foods.

An indirect enzyme-labeled antibody technique (ELAT), in which Salmonella typhimurium was used as a model, was developed as a method to detect Salmonella in food samples. A cellulose-acetate membrane filter, the matrix for detection, was placed on a membrane-filter base and overlaid with a multiwelled lucite template. Mixed broth enrichment cultures were dispensed in the template wells, and cells were spotted onto the membrane via suction. After fixation, the membranes were immersed in rabbit anti-S. typhimurium flagella antibody, washed, immersed in goat anti-rabbit antibody conjugated to peroxidase, and washed. Exposure of membranes to the substrates 3,3'-diaminobenzidine or benzidine resulted in development of brown or blue macroscopic reaction products, respectively, on spots containing S. typhimurium. ELAT results agreed with those of enrichment serology and cultural procedures on three food products containing known levels of S. typhimurium. Because of the magnification effect of the enzyme-substrate reaction, fewer cells were needed for detection than with enrichment serology, thereby reducing the total analysis time. The ability to test 14 or more samples simultaneously on a 47-mm membrane filter would facilitate screening large number of samples. Pending the development of a pure H antisera pool for the common Salmonella serotypes free from O antibodies, the ELAT demonstrated potential as a Salmonella detection methodology.     

alpha-Hydroxy-beta-keto-gamma-aminobutyric acid in human urine.

A new amino acid has been isolated from the normal human urine. The chemical structure of the amino acid was determined to be alpha-hydroxy-beta-keto-gamma-aminobutyric acid based on its physical properties involving NMR, infrared and mass spectra, as well as chemical degradation and synthesis. In six healthy adults the urinary contents of the new amino acid were 3.2--4.5 mumol/24 h.