Antibody against purified human hexosaminidase B cross-reacting with human hexosaminidase A

[Nephrotoxicity of aminoglycosides and cephalosporins. Value of examining the isoenzyme profile of N-acetyl-beta-D-glucosaminidase]

It is a well known fact that aminoglycosides increase urinary action of N-acetyl-beta-D-glucosaminidase (NAG) but the significance of this fact remains, as yet, nuclear. The aim of this study is firstly to attempt to form an explanation of the enzymatic effects of aminoglycosides by studying the excretion of A, B, I isoenzymes and by calculating the ratio A/B + I during gentamicin, tobramycin and amikacin therapy and secondly, by using this method, to try to propose a marker for evaluating nephrotoxicity. Our results indicate that all three antibiotics induce an increase in the excretion of the A-form, which is present freely in the lysosomes and in physiological urines, but that only gentamicin and tobramycin bring about an increase in the B-form associated with the lysosomal membrane. Since excretion of the B-form is associated with renal failure, it can be proposed as a good marker for evaluating nephrotoxicity. These observations allow us to advance the hypothesis that aminoglycosides determine an enzymatic inducing effect on the NAG synthesis with urinary excretion of the A-form by exocytosis whilst the excretion of the B-form, associated with the lysosomal membrane, would result from a rupture of this membrane. This lesion would bring about an excretion of toxic aminoside into the cytoplasm, causing damage to the mitochondrial apparatus. On the other hand isoenzymatic profiles, observed during cephalosporin treatment suggest a process of cellular necrosis.

Urinary N-acetyl-beta-D-glucosaminidase (NAG) isoenzyme profiles: a tool for evaluating nephrotoxicity of aminoglycosides and cephalosporins

The study of urinary NAG isoenzymes in different nephrotoxic states shows that each antibiotic is characterised by a specific isoenzyme profile which probably reflects the very nature of its toxic mechanism. Those aminoglycosides which are responsible for important elimination of B- and I-forms would directly induce the synthesis of these isoenzymes in the endoplasmic reticulum. Cephalosporins, which are less nephrotoxic, present profiles which are closer to those obtained for normal urine. A combination aminoglycoside plus cephalosporin, though globally more nephrotoxic than aminoglycosides alone, is characterised by relatively poorer profiles of B- and I-forms. This could be linked to the reciprocal interaction of one antibiotic with the toxic mechanisms of the other.

Inactivation of bovine kidney beta-N-acetyl-D-glucosaminidase by nonenzymatic glucosylation

Evidence is presented that the incubation of beta-N-acetyl-D-glucosaminidase from bovine kidney with glucose leads to the covalent incorporation of the sugar into the enzyme protein. Concomitantly, the enzyme activity becomes markedly reduced depending on the time of incubation and the concentration of glucose employed. The separate investigation of the isoenzymes A and B, as obtained after DEAE-cellulose chromatography of the preparation, revealed that isoenzyme A had lost some 80% of its initial activity after 15 days at 37 degrees C at 44.4mM glucose, whereas isoenzyme B activity remained unchanged. The inactivation of A was associated (1) with a marked decrease in protein stain intensity after polyacrylamide gel and Cellogel electrophoresis and (2) with the formation of a small amount of apparent isoenzyme B, as indicated by the following observations: (a) appearance of enzyme activity at the position of isoenzyme B after DEAE-cellulose chromatography, (b) appearance of protein with enzyme activity in the region of authentic isoenzyme B after Cellogel electrophoresis, (c) increase in molecular mass from 130 kDa to 205 kDa, (d) similarity in heat-stability and Km for p-nitrophenyl N-acetyl-beta-glucosaminide between glucose-treated isoenzyme A and authentic isoenzyme B. As in diabetes mellitus the activity of beta-N-acetyl-D-glucosaminidase has been reported to be decreased in kidney and other tissues, the possibility that nonenzymatic glucosylation of the enzyme might occur in vivo is considered.

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.

Purification and properties of human kidney-cortex hexosaminidases A and B

Hexosaminidases (EC 3.2.1.30) A and B from human kidney cortex were purified to homogeneity by using concanavalin A affinity chromatography, ion-exchange chromatography and gel filtration. The yield of homogeneous isoenzymes improved approx. 20-fold, giving preparations of hexosaminidases A and B with specific activities of about 200 and 325 units/mg of protein respectively. The kinetic and structural properties of kidney hexosaminidase isoenzymes were studied and compared with the hexosaminidase isoenzymes from human placenta. The amino acid composition of hexosaminidase A was significantly different from that of hexosaminidase B. In the event of success in developing enzyme-replacement therapy for Tay-Sachs and Sandhoff's diseases, this modified procedure can furnish larger amounts of homogeneous isoenzymes.

Interrelationship of hexosaminidases A and B: conformation of the common and the unique subunit theory

Human kidney hexosaminidase A (beta-N-acetylglucosaminidase; 2-acetamido-2-deoxy-beta-D-glucoside acetamidodeoxyglucohydrolase; EC 3.2.1.30) is a heteropolymer of two immunologically distinct subunits designated as alpha and beta. Hexosaminidase B, however, is a homopolymer comprised entirely of beta subunits. When human kidney hexosaminidase A was dissociated into its subunits by p-hydroxymercuribenzoate, three distinct proteins having isoelectric points of pH 7.2.5.4, and 4.3 were isolated. The fraction having an isoelectric point of pH 7.2, designated as beta fraction, was electrophoretically and immunologically identical to hexosaminidase B and was enzymatically active. The proteins having isoelectric points of pH 5.4 and 4.3, designated as hexosaminidase Ai and alpha fractions, respectively, were enzymatically inactive and crossreacted with antiserum against hexosaminidase A and not with antiserum against hexosaminidase B. Upon incubation of p-hydroxymercuribenzoate-treated hexosaminidase A with dithiothreitol,, hexosaminidase A activity, as well as antigenicity, was regenerated, indicating that alpha and beta subunits hybridize to form hexosaminidase A. Antibodies raised in rabbits against beta fractions reacted with both hexosaminidase A and B, whereas the antibodies against alpha and hexosaminidase Ai fractions reacted only against hexosaminidase A. This would indicate that both fractions are composed only of subunits unique to hexosaminidase A. The molecular weights of alpha,beta, and hexosaminidase Ai fractions were estimated to be 47,000, 120,000, and 180,000 respectively, by Sephadex gel filtration. Upon urea-sodium dodecyl sulfate polyacrylamide electrophoresis, each of the three fractions dissociated into a single polypeptide having a molecular weight of approximately 18,000. It is concluded that p-hydroxymercuribenzoate dissociates hexosaminidase A, (alphabeta)3, into its subunits, and the beta subunits can reassociate to form relatively stable hexosaminidase B, (betabeta)3, while the alpha subunits reassociate in both the dimeric state, alpha2, and a polymeric state, alpha8.

Characterization and tissue distribution of N-acetyl hexosaminidase C: suggestive evidence for a separate hexosaminidase locus

1. An electrophoretic system in which N-acetyl hexosaminidase C (HEX(C)) MIGRATES LESS ANODALLY THAN N-acetyl hexosaminidase A (HEX(A)) is described. 2. HEX(C) is shown to differ from HEX(A) and HEX(B) in substrate specificity, molecular size and affinity for Concanavalin-A. 3. HEX(C) is present in a wide range of adult and foetal tissues and in tissues from patients with Tay-Sachs and Sandhoff's diseases. It is particularly prominent in brain, testis, thymus and lymphoblastoid cell extracts and in several foetal tissues. 4. It is suggested that HEX(C) is coded at a separate gene locus from HEX(A) and HEX(B).

Immunological characterization of human liver alpha-D-mannosidase

Antiserum was raised against purified human liver alpha-D-mannosidase B. It precipitated alpha-mannosidases A and B from solution, demonstrating the close structural resemblance of these 2 forms of acidic alpha-mannosidase activity. A continuous enzymically active precipitin line with no spurs was obtained when alpha-mannosidase A and B were placed in adjacent wells on Ouchterlony double-diffusion plates. The antiserum precipitated acidic but not neutral alpha-mannosidase from an extract of human liver, confirming that the acidic and neutral activities are not closely related. Acidic activity was also precipitated from extracts of human brain, kidney and leucocytes by the antiserum. However, it did not cross-react with bovine acidic alpha-mannosidase activity or with the activity in human plasma that has an optimum pH of 5.5. The two acidic forms of human liver alpha-mannosidase, A and B, are immunologically identical but distinct from neutral alpha-mannosidase and that activity with an optimum pH of 5.5.

Studies on beta-D-N-acetylhexosaminidase. Various isozymes in tissues of normal subjects and Sandhoff's disease patients

Hexosaminidase (EC 3.2.1.51) activity from human liver and kidney extract was completely precipitated by anti-hexosaminidase A antiserum and 80 to 90% by anti-hexosaminidase B antiserum. Immunologically distinct hexosaminidase "C" could not be detected in these tissues. The final fractions of hexosaminidase A eluted from DE-52 chromatography were resolved into several enzymatically active components by rechromatography. Compared to hexosaminidase A and B, these minor components are more anodal in polyacrylamide disc electrophoresis. The residual activity of hexosaminidase from liver and fibroblasts of patients with Sandhoff's disease has also been resolved into similar components. The enzyme activity of these more anodal hexosaminidase components was precipitated completely by anti-hexosaminidase A anti-serum and partially by anti-hexosaminidase B antiserum. The minor, more anodal components probably represent hexosaminidase molecules having an altered ratio of subunits or the degradation products of hexosaminidase A.

A study of hexosaminadases in interspecific hybrids and in GM2 gangliosidosis with a discussion on their genetic control

1. Hexosaminidases were studied by electrophoresis with different human fibroblast extracts. We found in the same conditions of detection and culture three bands from the cathode to the anode, namely Hex B, Hex A, Hex C for the normal fibroblast, Hex B for the two different Tay-Sachs and Hex C for the two unrelated Sandhoff patients. 2. The analysis of man-rodent hybrids (hamster and mouse with normal and Sandhoff human fibroblasts) indicates a probable synteny between MPI, Hex C, "Hex A fast", and "Hex A-like". "Hex A fast" is probably a man-hamster hybrid enzyme, "Hex A-like" a man-mouse enzyme. Our data agree with the model of Ropers and Schwantes (Hex C = (alphaalpha)n; Hex A = (alphabeta)n; Hex B = (betabeta)n). Probably Hex A-fast = (alphabeta')n with hamster Hex B' = (beta'beta')n; and Hex A-like = (alphabeta1)n with mouse Hex B1 = (beta1beta1)n; and probably n = 2 according to the tetrameric structure model of Tallman et al. (1974). 3. As an explanation of the results given by Poenaru et al. (anti Hex A reacts with Hex A and Hex B but not with Hex C) we propose the existence of a compound antigen (alphabeta) for Hex A. Anti Hex A specific = anti (alphabeta); anti Hex A non-specific = anti Hex B = anti B, anti alpha being absent or negligible. 4. In our opinion, the Tay-Sachs mutation opposes the alphaB association while the alphaalpha association is possible at a low rate or unstable; it is thus possible to observe Hex C in certain conditions, e.g. in foetal brain. 5. We present a discussion about the genetic control of hexosaminidases, GM2 gangliosidosis, and the possible localization of the different mutations in the variants.

Rabbit beta-glucuronidase. Subcellular distribution and immunochemical properties

1. The subcellular distribution of beta-glucuronidase and other hydrolases in rabbit liver was investigated. beta-Glucuronidase was found in both microsomal and lysosomal fractions. 2. Multiple forms of beta-glucuronidase were present in extracts of microsomal and lysosomal fractions. All forms were common to both fractions. 3. A specific antiserum against beta-glucuronidase was raised, and characterized by immunoprecipitation and affinity-chromatography procedures. 4. The immunological identity of the multiple forms in the pure beta-glucuronidase preparation, and the immunological identity of the beta-glucuronidase complement of lysosomal extracts with that of microsomal extracts, were demonstrated by means of the antiserum. The presence of inactive enzyme in various enzyme preparations was shown.

A low-molecular-weight protein cross-reacting with human liver N-acetyl-beta-D-glucosaminidase

Antisera were raised to preparations of hexosaminidase isoenzymes A and B purified from human liver. Protein that cross-reacted with the liver hexosaminidase was detected by an antibody-consumption method. A cross-reacting protein with a low molecular weight (20000) was partially characterized and purified from control human liver. This protein is also present in the liver of patients with Tay-Sachs disease or with Sandhoff's disease. Hexosaminidases A and B gave an immunological reaction of partial identity with the low-molecular-weight protein. The possible identity of the low-molecular-weight cross-reacting protein as a subunit of hexosaminidase is discussed.

N-acetyl-beta-hexosaminidase: role in the degradation of glycosaminoglycans

Extracts of cultured normal human skin fibroblasts released radioactivity from a (14)C-labeled heptasaccharide prepared by addition of [(14)C]N-acetylgalactosamine to the nonreducing terminus of a hexasaccharide derived from chondroitin 4-sulfate whereas fibroblast extracts from patients with Tay-Sachs and Sandhoff-Jatzkewitz diseases did not. The results suggest that N-acetyl-beta-hexosaminidase A is responsible for degradation of the oligosaccharide substrate.

Immunological properties of N-acetyl-beta-D-glucosaminidase of normal human liver and of GM2-gangliosidosis liver

Antisera were raised to a partially purified preparation of human liver hexosaminidase and to highly purified preparations of hexosaminidase isoenzymes A and B. All the antisera precipitated the enzyme in an enzymically active form, which could be located on immunodiffusion and immunoelectrophoretic gels by using a histochemical substrate. The antisera to the purified isoenzymes were shown to react with hexosaminidase from human liver, kidney, brain and spleen, but did not cross-react with human liver beta-glucosidase, beta-galactosidase, alpha-mannosidase, beta-xylosidase, arylsulphatase or acid phosphatase. Hexosaminidases A and B were immunologically identical. The immunological properties of the hexosaminidases from livers of patients with three types of GM(2)-gangliosidoses were closely similar. No evidence could be found for cross-reacting material in enzyme-deficient states.