Analyses of catalytic activity and inhibitor binding of human acid beta-glucosidase by site-directed mutagenesis. Identification of residues critical to catalysis and evidence for causality of two Ashkenazi Jewish Gaucher disease type 1 mutations

Analyses of catalytic properties and inhibitor binding were conducted to investigate the molecular basis of active site function of human acid beta-glucosidases (EC 3.2.1.45) expressed from normal and Gaucher disease Type 1 alleles. Comparative studies were conducted with enzymes expressed from natural (spleen and fibroblasts) alleles or from mutagenized cDNAs in Spodoptera frugiperda (Sf9) cells using the baculovirus expression system. Mutant cDNAs containing Thr43 to Lys43 (beta-GlcThr43----Lys) and Asp358 to Glu358 (beta-GlcAsp358----Glu) substitutions and two cDNAs containing Ashkenazi Jewish Gaucher disease Type 1 mutations, Arg120 to Gln120 (beta-GlcArg120----Gln) and Asn370 to Ser370 (beta-GlcAsn370----Ser) were expressed and the gene products characterized by enzymatic, immunologic, and inhibitor studies. Genotypes at the acid beta-glucosidase locus in selected Gaucher disease Type 1 patients were determined by allele-specific oligonucleotide hybridization of amplified genomic DNA. Compared with normal, recombinant or natural enzymes expressed from beta-GlcAsn370----Ser alleles had about 2-5-fold decreased specific activity based on CRIM (cross-reacting immunologic material). The beta-GlcArg120----Gln cDNA expressed catalytically inactive CRIM in Sf9; consistent with the 9-fold decreased CRIM-specific activity of the natural enzyme from a beta-GlcArg120----Gln/beta-GlcAsn370----Ser genetic compound. The beta-GlcAsp358----Glu cDNA expressed catalytically inactive CRIM in Sf9 cells. The presence of natural or recombinant enzyme expressed from beta-GlcAsn370----Ser alleles was sufficient to confer 3-5-fold increased IC50 values for deoxynojirimycin, glucosylsphingosine, and N-alkyl-glucosylamine derivatives. Progress curves for inhibition by the slow-tight binding N-alkyl-glucosylamines indicated that the beta-Glc-Asn370----Ser mutation did not alter a conformational change induced by these reaction intermediate analogues. These results provide evidence that the beta-GlcArg120----Gln and beta-GlcAsn370----Ser mutations found in Gaucher disease Type 1 patient genomes are the molecular bases of the enzymatic dysfunction. In addition, the region including Arg120 and that encompassing Asp358 and Asn370 contain residues critical to active site formation or participation in the catalytic mechanism.

Acid beta-glucosidase: enzymology and molecular biology of Gaucher disease

Human lysosomal beta-glucosidase (D-glucosyl-acylsphingosine glucohydrolase, EC 3.2.1.45) is a membrane-associated enzyme that cleaves the beta-glucosidic linkage of glucosylceramide (glucocerebroside), its natural substrate, as well as synthetic beta-glucosides. Experiments with cultured cells suggest that in vivo this glycoprotein requires interaction with negatively charged lipids and a small acidic protein, SAP-2, for optimal glucosylceramide hydrolytic rates. In vitro, detergents (Triton X-100 or bile acids) or negatively charged ganglioside or phospholipids and one of several "activator proteins" increase hydrolytic rate of lipid and water-soluble substrates. Using such in vitro assay systems and active site-directed covalent inhibitors, kinetic and structural properties of the active site have been elucidated. The defective activity of this enzyme leads to the variants of Gaucher disease, the most prevalent lysosomal storage disease. The nonneuronopathic (type 1) and neuronopathic (types 2 and 3) variants of this inherited (autosomal recessive) disease but panethnic, but type 1 is most prevalent in the Ashkenazi Jewish population. Several missense mutations, identified in the structural gene for lysosomal beta-glucosidase from Gaucher disease patients, are presumably casual to the specifically altered posttranslational oligosaccharide processing or stability of the enzyme as well as the altered in vitro kinetic properties of the residual enzyme from patient tissues.

Resting energy expenditure in Gaucher's disease type 1: effect of Gaucher's cell burden on energy requirements

The resting energy expenditure (REE; kcal/d) of 25 patients with Gaucher's disease type 1 was determined by indirect calorimetry. The average observed REE for the group was approximately 44% greater (P less than .01) than that predicted (predicted REE) for these patient's age, sex, height, and weight. The increased caloric requirements of these patients was manifested by a height-for-age less than or equal to the fifth percentile in seven of nine growing children and a muscle mass of less than the fifth percentile in 15 of 19 patients studied. The excess REE (observed REE--predicted REE) for individual Gaucher's disease type 1 patients was directly related to their liver volume as estimated from radionuclide scans and to the mass of the spleen as measured at splenectomy. The relationship between spleen mass and excess REE was demonstrated by an average 22.0% decrease in REE following splenectomy in five patients. Based on these data, the metabolic rate of the splenic tissue removed from the patients was calculated to be 96.8 kcal/d/kg, about twofold to threefold less than that of normal splenic tissue. These findings indicate that the elevated REE observed in these patients resulted from the large mass of Gaucher's cells, which although individually hypometabolic, were cumulatively an excessive metabolic burden. Furthermore, they suggest that indirect calorimetry may be a quantitative tool for measuring disease progression and the effect of therapeutic intervention in Gaucher's disease type 1.

Comparison of RNase A, a chemical cleavage and GC-clamped denaturing gradient gel electrophoresis for the detection of mutations in exon 9 of the human acid beta-glucosidase gene

Gaucher disease (GD), which results from mutations in the human acid beta-glucosidase (beta-Glc) gene, was used as a model system to compare the utility of three methods capable of detecting single base substitutions. PCR-amplified beta-Glc exon 9 sequences of GD patients were screened for single base mutations by GC-clamped denaturing gradient gel electrophoresis (DGGE) and RNase A cleavage of RNA-DNA heteroduplexes, and by chemical (hydroxylamine/osmium tetroxide) cleavage of dsDNA heteroduplexes. PCR products showing abnormal behaviour were cloned and sequenced. Three new point mutations were detected by this strategy. A G to C (Asp409 to His409) substitution was present in two Type 1 and one Type 3 GD patients; an A to T transversion (Asp409 to Val409) was detected in only a single Type 3 individual, and a G to T mutation (Val394 to Leu394) was present in one Type 1 and one Type 3 patient. GD thus exhibits extensive molecular heterogeneity, with at least five single base mutations in beta-Glc exon 9. In every case verified by ASO hybridization, DGGE had correctly identified the presence of the three new mutations, as well as the two previously described exon 9 mutations. In comparison, although RNase A and the chemical method were both able to detect some of these mutations, neither method reproducibly detected all of them. Additionally, DGGE was the only method that was able to reliably determine whether a given mutation was present homozygously or heterozygously. These results suggest that GC-clamped DGGE may be a more reliable and informative screening method for point mutation detection.

Molecular cloning of a human co-beta-glucosidase cDNA: evidence that four sphingolipid hydrolase activator proteins are encoded by single genes in humans and rats

Authentic cDNAs encoding the activator protein for acid beta-glucosidase (EC3.2.1.45), co-beta-glucosidase, were cloned from the pCD and lambda gt11 human cDNA libraries. Initial screening with oligonucleotide mixtures encoding amino acid sequences of co-beta-glucosidase identified partial cDNAs which were used to obtain a potentially full-length cDNA from the lambda gt11 library. This clone (2767 bp), EGTISI, contained 5' (38 bp) and 3' (1157 bp) noncoding sequences, a translation initiation site, and an open reading frame encoding 524 amino acids which included a typical hydrophobic signal sequence (16 amino acids). Computer analyses identified three regions of high similarity to co-beta-glucosidase encoded by tandem sequences in EGTISI. Searches revealed that two of these regions encoded peptides of known function; SAP1 (sphingolipid activator protein 1) and protein C (a new sphingolipid activator protein) were encoded by EGTISI sequences 5' and 3', respectively, to those for co-beta-glucosidase. The third region of similarity, encoding a theoretical peptide (undefined function), was located most 5' in the cDNA. EGTISI and its encoded polypeptide had high similarity (77% nucleotide identity and about 80% amino acid similarity) to a rat Sertoli cell cDNA and its encoded sulfated glycoprotein-1. These results indicate that a single highly conserved gene encodes the precursor for four potential sphingolipid activator proteins in rat and man.

Gaucher disease: molecular heterogeneity and phenotype-genotype correlations

Gaucher disease (GD) is the most prevalent lysosomal storage disease. This autosomal recessive trait results from the defective activity of acid beta-glucosidase (beta-Glc). Four different exonic point mutations have been identified as causal alleles for GD. To facilitate screening for these alleles, assays were developed using allele-specific oligonucleotide hybridization to amplified genomic DNA sequences. Specifically, intron bases flanking exons 5, 9, and 10 were determined, and conditions for PCR amplification of these exons were obtained. Two different procedures were developed to distinguish signals obtained from the structural beta-Glc gene exons and those from the pseudogene. These procedures were used to determine the distribution of all known GD alleles in a population of 44 affected patients of varying phenotypes and ethnicity. The high frequency of one of the exon 9 mutations in Ashkenazi Jewish GD type 1 patients was confirmed, and, in addition, this mutation was present in ethnically diverse non-Jewish type 1 GD patients. Homozygotes (N = 5) for this allele were midly affected older individuals, and this mutant allele was not found in any patient with neuronopathic disease. The exon 10 mutation was confirmed as the predominant allele in types 2 and 3 GD. However, several type 1 GD patients, including one of Ashkenazi-Jewish heritage, also were heterozygous for this allele. The presence of this allele in type 1 patients did not correlate with the severity of clinical symptoms. The second exon 9 mutation and the exon 5 mutation were rare, since they occurred only heterozygously either in one type 2 GD patient or in two related Ashkenazi-Jewish GD patients, respectively. Although most GD patients (38 of 44) had at least one of the known mutant alleles, 57% were heterozygotes for only one of these mutations. Fourteen percent of patients were negative for all mutations. A total of 73% of GD patients had at least one unknown allele. The varying clinical phenotypes and ethnic origins of these incompletely characterized patients suggest that multiple other GD alleles exist.

Gaucher disease: fate of the splenic remnant after partial splenectomy--a case of rapid enlargement

In Gaucher disease, partial splenectomy has been suggested for alleviating the complications of splenomegaly as well as for avoiding the immunologic compromise and potential acceleration of bony and hepatic involvement that may follow total splenic resection. However, the fate of the splenic remnant has been reported rarely. A subtotal splenectomy (85%) was performed in a 19-month-old girl with rapidly progressing Gaucher disease and massive splenomegaly (12% of body weight). Within 3 months, the splenic remnant had increased four-fold in size. Previous reports indicated only three Gaucher patients had significant enlargement of the splenic remnant after partial splenectomy. These findings indicate that splenomegaly may recur rapidly in Gaucher disease following partial splenectomy.

Posttranslational processing of human lysosomal acid beta-glucosidase: a continuum of defects in Gaucher disease type 1 and type 2 fibroblasts

The major processing steps in the maturation of the lysosomal hydrolase, acid beta-glucosidase, were examined in fibroblasts from normal individuals and from patients with types 1 and 2 Gaucher disease. In pulse-chase studies with normal fibroblasts, remodeling of N-linked oligosaccharides resulted in the temporal appearance of three molecular-weight forms of acid beta-glucosidase. An initial 64-kDa form, containing high mannose-type oligosaccharide side chains, was processed quantitatively, within 24 h, to a sialylated 69-kDa form. During the subsequent 96 h, some of the 69-kDa form is processed to 59 kDa. Glycosidase digestion studies revealed that the increase in the apparent molecular weight of the normal enzyme from 64 kDa to 69 kDa resulted primarily from the addition to sialic acid residues in the Golgi apparatus. The polypeptide backbone of both the 64-kDa and 69-kDa forms was 55.3 kDa. Processing of acid beta-glucosidase in fibroblasts from three of four type 1 (nonneuronopathic) Ashkenazi Jewish Gaucher disease patients was nearly normal. With fibroblasts from one Ashkenazi Jewish and three non-Jewish type 1 as well as from two type 2 (acute neuronopathic) Gaucher disease patients, only a 64-kDa form of acid beta-glucosidase was detected. Inefficient and incomplete processing to the 69-kDa form was found in one type 2 cell line (GM2627). These results indicate that no firm correlation exists between the type or degree of abnormal processing of acid beta-glucosidase in fibroblasts and the phenotype of Gaucher disease.

Expression of functional human acid beta-glucosidase in COS-1 and Spodoptera frugiperda cells

A cDNA encoding human acid beta-glucosidase (N-acylsphingosyl-1-O-beta-D-glucoside: glucohydrolase, EC 3.2.1.45) expressed catalytically active enzyme in transfected COS-1 or infected Spodoptera frugiperda (Sf9) cells. The expression plasmid p91023(B) (p91023B/Glc) and a Baculovirus (AcMNPV/Glc) containing the cDNA were constructed and used with the respective cells. By immunoblotting a glycosylated, 63-kilodalton human acid-beta-glucosidase was detected in the transfected or infected cells. A 56-kilodalton human polypeptide was obtained after complete deglycosylation with N-Glycanase. The expressed human enzymes also had partial endoglycosidase H sensitivity. The human enzyme expressed at high levels in Sf9 cells and had normal immunologic properties. With the partially purified enzyme from Sf9 cells, intact function of active site was indicated by normal kcat and Kmapp or Kiapp values for alternative substrates or potent inhibitors, respectively. The expressed enzyme was also activated normally by the negatively charged lipid, taurocholate. The results of these studies indicate that the Baculovirus expression system could provide a convenient source of normal human enzyme for structure/function investigations. In addition, this expression system should prove useful for the identification and evaluation of putative etiologic point mutations in Gaucher disease variants with kinetically altered residual enzymes.

Gaucher disease type 1: cloning and characterization of a cDNA encoding acid beta-glucosidase from an Ashkenazi Jewish patient

Gaucher disease (GD) type 1 is the most prevalent lysosomal storage disease and the most prevalent genetic disease among the Ashkenazi Jews. The defective activity of acid beta-glucosidase is the enzymatic basis of GD and is inherited as an autosomal recessive trait. To investigate the genetic basis of Ashkenazi Jewish GD type 1, a cDNA encoding acid beta-glucosidase was isolated from a cDNA library constructed using splenic poly(A)+RNA from a patient. The cDNA was sequenced to identify mutations, and the presence of a single missense mutation in the patients' genome was confirmed by selective oligonucleotide hybridization and by restriction endonuclease digestion analyses of amplified genomic sequences. This G----A transition (Arg-119 to Gln-119) was present heterozygously in the index patient and his affected third cousin but was not present in normal non-Jewish individuals. This mutation is the second single base mutation found in Ashkenazi Jewish GD type 1 patients. Furthermore, results obtained with the affected third cousin suggest that at least three mutant alleles may be present in this GD subpopulation.

Hexosaminidase A activity and amyotrophic lateral sclerosis

Abnormalities of GM2 ganglioside metabolism owing to hexosaminidase A (Hex A) deficiency have been associated with ALS phenotypes. The clinical features described in these ALS patients with Hex A deficiency include early onset, positive family history, and/or long disease duration. In an attempt to determine prospectively the incidence of Hex A deficiency within an ALS population, the records of The Mount Sinai Medical Center ALS Clinic were reviewed to select those patients with "atypical" ALS (total N = 52), i.e. onset before age 35, positive family history, and/or disease duration greater than 90 months. The control group (total N = 50), "typical" ALS patients, did not fulfill any of these historical criteria. Hex A activity determined in isolated peripheral blood leukocytes was normal in all typical ALS patients (mean 67.3%). Hex A deficiency was not found in any atypical ALS patients. Thus, Hex A deficiency apparently is an unusual etiology of typical or atypical ALS but is of medical and genetic importance in individual families.

Abnormalities in lipoprotein metabolism in Gaucher type 1 disease

We have previously described an association between Gaucher type 1 disease and reduced levels of total, low density lipoprotein (LDL), and high density lipoprotein (HDL) cholesterol. Plasma concentrations of apolipoprotein B and apolipoprotein AI were reduced in these subjects, while plasma apolipoprotein E (apoE), which can be synthesized and secreted by macrophages, was increased. To study the pathophysiologic basis for these changes in lipoprotein and apolipoprotein levels, we studied very low density lipoprotein (VLDL), LDL, and HDL metabolism in-depth in four subjects with Gaucher disease. Gel filtration of their plasma revealed that apoE was present in essentially a single population of lipoproteins in the large HDL range. In subject no. 4, studied presplenectomy and post-splenectomy, plasma apoE levels fell after surgery in association with a redistribution of apoE among the plasma lipoproteins to a pattern seen in normal subjects. Determination of the rates of secretion and catabolism of VLDL apoB and triglyceride were within normal limits. The reduced plasma levels of LDL and HDL cholesterol, and of both plasma apoB and apoAI, were associated with increased fractional catabolic rates of these apolipoproteins in LDL and HDL. These results indicate that the hypocholesterolemia present in subjects with Gaucher type 1 disease is associated with increased fractional catabolism of LDL and HDL. These findings, together with the evidence for alternations in plasma apoE metabolism in this disorder, suggest a role for the macrophage as the basis for these abnormalities.

Human acid beta-glucosidase: inhibition studies using glucose analogues and pH variation to characterize the normal and Gaucher disease glycon binding sites

Comparative kinetic studies with glycon inhibitors were used to investigate the properties of the active site of human acid beta-glucosidase (EC 3.2.1.45) from normal placenta and spleens of type 1 Ashkenazi Jewish Gaucher disease (AJGD) patients. With the pure normal enzyme, the specificity of glycon binding was assessed with 35 glucose derivatives and epimers. Most glycons were mixed type inhibitors with a predominantly competitive nature (i.e., Kis much less than Kii) and had low apparent affinity for the enzyme (Kisapp = 20-500 mmol/l). beta-Glucose-1-phosphate was unusual, since it inhibited 4-methylumbelliferyl-beta-glucoside hydrolysis in an uncompetitive pattern (Kiapp = 0.55 mmol/l) but had no effect on glucosyl ceramide hydrolysis. C-1- (1-deoxy-1-amino-beta-D-glucose) and C-3- (3-deoxy-3-amino-D-glucose) amino and C-5-imino [1-deoxynojirimycin (dNM), nojirimycin and castanospermine] substituted sugars were highly potent inhibitors with Kisapp(beta-glucose)/Kisapp approximately equal to 10(3)-10(5); an amine at C-2 did not alter Kisapp compared to beta-glucose. The variation of Kisapp with pH for the 5-imino- and 1-deoxy-1-aminoglycosides conformed to a model for the unprotonated inhibitors binding to the protonated forms (EH and EH2) of the diprotic (Vmaxapp and Vmaxapp/Kmapp) normal enzyme (pK1 = 4.7; pK2 = 6.7) with pH-independent Kisapp values of 2.9-9.0 mumol/l and 0.22 mmol/l, respectively. Several of the amine-containing inhibitors competitively protected the enzyme from inactivation by conduritol B epoxide, a covalent active site-directed inhibitor, indicating interaction with residues at that site. With the partially purified AJGD splenic enzymes, the results were the same except that Kisapp(AJGD)/Kisapp(normal) = 4-17 for dNM and 1-deoxy-1-amino-beta-glucose; this ratio was approximately equal to 1 with most other glycons, and particularly, nojirimycin and castanospermine. The results of these studies indicated that the glycon binding site of the normal acid beta-glucosidase contains important residues for interaction with the C-2, C-3 and C-4 hydroxyl groups of beta-glucose and a residue with pKa = 6.7 which was critical to the binding of amine-containing inhibitors and the hydrolysis of substrates. The findings were consistent with a specific alteration in or near the glycon binding site which results in the functional abnormalities of the mutant AJGD acid beta-glucosidase.

Human acid beta-glucosidase: use of inhibitors, alternative substrates and amphiphiles to investigate the properties of the normal and Gaucher disease active sites

Comparative studies with lipoidal inhibitors and alternative substrates were conducted to investigate the properties of the active site of human acid beta-glucosidase (D-glucosyl-N-acylsphingosine glucohydrolase, EC 3.2.1.45) from normal placenta and spleens of Type 1 Ashkenazi Jewish Gaucher disease (AJGD) patients. With the normal enzyme, the inhibitory potencies of series of alkyl(Cn; n = 0-18)amines, alkyl beta-glucosides and alkyl-1-deoxynojirimycins were a biphasic function of increasing chain length: i.e., large decreases in Ki,app or IC50 were found only with n greater than 4 and limiting values were approached with n = 12-14. This biphasic function of alkyl chain length was observed in the presence or absence of detergents and/or negatively charged lipids. In the presence of Triton X-100 concentrations greater than the critical micellar concentration, the relative (to deoxynojirimycin) inhibitory potencies of the N-Cn-deoxynojirimycins (n greater than 4) were decreased about 3-5-fold, due to an energy requirement to extract the inhibitors from Triton X-100 micelles. The Ki,app or IC50 of N-hexylglucosylsphingosine was inversely related to the Triton X-100 concentration and was not affected by the presence of 'co-glucosidase'. The mutual exclusion of glucon, N-Cn-deoxynojirimycin and sphingosine derivatives from the normal enzyme suggested a shared region for binding in the active site. Increasing the fatty-acid acyl chain length of glucosyl ceramide from 1 to 24 carbons had minor effects on Km,app ( = Kis,app) (8-40 microM), but increased Vmax,app up to 13-fold. With the AJGD enzyme, the inhibitor and alternative substrate findings were similar to those with the normal enzyme, except that Kis,app(AJGD)/Kis,app(normal) = 4 to 11 for the Cn-glycons and sphingosine derivatives. These results indicated that (1) the Ki,app or Km,app values for amphiphilic inhibitors or substrates reflect a balance of binding energies for two hydrophobic subsites within the enzyme's active site and Triton X-100 micelles and (2) the abnormal properties of the AJGD enzyme result from an amino-acid alteration(s) within or near a hydrophilic region which is shared by the glycon-binding site and the two hydrophobic sites of the active site.

Gaucher disease: genetic heterogeneity within and among the subtypes detected by immunoblotting

The genetic heterogeneity of Gaucher disease subtypes and variants was investigated by immunoblotting of fibroblast extracts. For these studies polyclonal and monoclonal antibodies were raised to acid beta-glucosidase preparations containing a single N-terminal amino acid sequence that was colinear with that encoded by the beta-Glc cDNAs. Three forms (Mr approximately equal to 67,000, 64,000-61,000, and 58,000) of cross-reacting immunologic material (CRIM) were observed in control individuals. Decreased amounts of the same CRIM forms were detected in most type 1 Gaucher disease patients, but single CRIM forms of variable molecular weight were observed in several non-Jewish type 1 variants. One or two CRIM forms of variable molecular weight were found in neuronopathic (type 2 and type 3) patients. The amount of CRIM was severely decreased in the majority of the type 2 and type 3 patients; one American black type 2 patient was CRIM negative. With this one exception, one CRIM form was detected in the cell-free culture media from all normal or Gaucher disease fibroblasts that had an Mr approximately 2,000 greater than the highest respective intracellular molecular-weight form. All intra- or extracellular CRIM forms were reduced to a single form after deglycosylation with N-Glycanase. In addition, the radioactivity from [3H]Br-conduritol B epoxide, a specific covalent inhibitor of beta-Glc, localized to the CRIM forms of beta-Glc on immunoblots. These results indicate that all subtypes and variants of Gaucher disease result from mutations that alter the stability and/or processing of beta-Glc. Furthermore, the heterogeneity of the CRIM patterns within and among the variants of Gaucher disease cause the diagnostic usefulness of immunoblotting to be restricted to those families in which the phenotype has been well established.

Human acid beta-glucosidase: Northern blot and S1 nuclease analysis of mRNA from HeLa cells and normal and Gaucher disease fibroblasts

Human acid beta-glucosidase (beta-Glc) mRNA was evaluated by dot blot, Northern blot, and S1 nuclease analyses of extracts of HeLa cells and cultured fibroblasts from normal individuals and Gaucher disease patients. Dot blot quantitation indicated an equal concentration of specific mRNA in all sources. Northern blot analyses demonstrated the presence of three poly (A)+ mRNAs of about 5,600, 2,500, and 2,000 nucleotides in length from all cell extracts. All three mRNAs were present in normal amounts in fibroblast extracts from several subtypes and variants of Gaucher disease. The largest poly (A)+ mRNA species was thought to represent an unspliced nuclear precursor for the two smaller beta-Glc mRNAs. S1 nuclease analyses, using SP6 transcripts of beta-Glc cDNA, indicated that the 2,000 nucleotide mRNA differs from the 2,500 nucleotide form at both the 5' and 3' ends. These results are consistent with the use of an alternate 5' splice site and 3' polyadenylation signal. These results also suggest that the subtype and variants of Gaucher disease result from single base alterations that lead to the synthesis of defective beta-Glc.

Gaucher's disease type 1: assessment of bone involvement by CT and scintigraphy

The effectiveness of CT and technetium-99m sulfur colloid (99mTc SC) bone-marrow scans in determining the extent and severity of skeletal involvement in 23 patients with type 1 Gaucher's disease was compared with the effectiveness of conventional radiographic techniques and technetium-99m methylene diphosphonate (99mTc MDP) bone scintigrams. Density measurements obtained by CT proved sensitive in differentiating normal marrow (-50 to -120 H). Scintigrams with the sulfur colloid nuclide demonstrated three distinct patterns of uptake: peripheral expansion of normal marrow (profile B), greater marrow expansion with patchy areas lacking uptake (profile C), and greater loss of uptake with retention of the nuclide in other reticuloendothelial organs and circulation (profile D). CT scans provided greater sensitivity in resolving the extent of marrow involvement in affected areas, while the 99mTc SC scintigrams were more effective in overall assessment of the severity of bone-marrow involvement. Both conventional radiographic techniques and 99mTc MDP bone scans were useful primarily as screening procedures or for evaluating specific involved areas. 99mTc MDP scans were useful in evaluating regional defects (i.e., ischemic necrosis) in certain cases, but no consistent patterns were observed. CT and 99mTc SC scans are useful for determining the extent and severity of Gaucher's disease involvement of bone marrow.

Human acid beta-glucosidase. Use of conduritol B epoxide derivatives to investigate the catalytically active normal and Gaucher disease enzymes

Human acid beta-glucosidase (glucosylceramidase; EC 3.2.1.45) cleaves the glycosidic bonds of glucosyl ceramide and synthetic beta-glucosides. Conduritol B epoxide (CBE) and its brominated derivative are mechanism-based inhibitors which bind covalently to the catalytic site of acid beta-glucosidase. Procedures using brominetritiated CBE and monospecific anti-human placental acid beta-glucosidase IgG were developed to determine the molar concentrations of functional acid beta-glucosidase catalytic sites in pure placental enzyme preparations from normal sources; kcat values then were calculated from Vmax = [Et]kcat using glucosyl ceramide substrates with dodecanoyl (2135 +/- 45 min-1) and hexanoyl (3200 +/- 410 min-1) fatty acid acyl chains and 4-alkyl-umbelliferyl beta-glucoside substrates with methyl (2235 +/- 197 min-1), heptyl (1972 +/- 152 min-1), nonyl (2220 +/- 247 min-1), and undecyl (773 +/- 44 min-1) alkyl chains. The respective kcat values for acid beta-glucosidase in a crude normal splenic preparation were about 60% of these values. In comparison, the kcat values of the mutant splenic acid beta-glucosidase from two Type 1 Ashkenazi Jewish Gaucher disease (AJGD) patients were about 1.5-3-fold decreased and had Km values for each substrate which were similar to those for the normal acid beta-glucosidase. The interaction of the normal and Type 1 AJGD enzymes with CBE in a 1:1 stoichiometry conformed to a model with reversible EI complexes formed prior to covalent inactivation. With CBE, the equal kmax values (maximal rate of inactivation) for the normal (0.051 +/- 0.009 min-1) and Type 1 AJGD (0.058 +/- 0.016 min-1) enzymes were consistent with the minor differences in kcat. In contrast, the Ki value (dissociation constant) (839 +/- 64 microM) for the Type 1 AJGD enzymes was about 5 times the normal Ki value (166 +/- 57 microM). These results indicated that the catalytically active Type 1 AJGD acid beta-glucosidase had nearly normal hydrolytic capacity and suggested an amino acid substitution in or near the acid beta-glucosidase active site leading to an in vivo instability of the mutant enzymatic activity.

Human acid beta-glucosidase: isolation and amino acid sequence of a peptide containing the catalytic site

Human acid beta-glucosidase (D-glucosyl-N-acylsphingosine glucohydrolase, EC 3.2.1.45) cleaves the glucosidic bonds of glucosylceramide and synthetic beta-glucosides. The deficient activity of this hydrolase is the enzymatic defect in the subtypes and variants of Gaucher disease, the most prevalent lysosomal storage disease. To isolate and characterize the catalytic site of the normal enzyme, brominated 3H-labeled conduritol B epoxide (3H-Br-CBE), which inhibits the enzyme by binding covalently to this site, was used as an affinity label. Under optimal conditions 1 mol of 3H-Br-CBE bound to 1 mol of pure enzyme protein, indicating the presence of a single catalytic site per enzyme subunit. After V8 protease digestion of the 3H-Br-CBE-labeled homogeneous enzyme, three radiolabeled peptides, designated peptide A, B, or C, were resolved by reverse-phase HPLC. The partial amino acid sequence (37 residues) of peptide A (Mr, 5000) was determined. The sequence of this peptide, which contained the catalytic site, had exact homology to the sequence near the carboxyl terminus of the protein, as predicted from the nucleotide sequence of the full-length cDNA encoding acid beta-glucosidase.

Human acid beta-glucosidase: affinity purification of the normal placental and Gaucher disease splenic enzymes on N-alkyl-deoxynojirimycin-sepharose

Two sepharose-bound 1-deoxynojirimycin N-alkyl derivatives, N-(9-carboxynonyl)- and N-(11-carboxyundecyl)-deoxynojirimycin, were used for the affinity purification of acid beta-glucosidase (beta-Glc) from normal and type-1 Ashkenazi Jewish Gaucher disease (AJGD) sources. The capacities of these nondegradable inhibitor supports were 0.5 and 0.75 mg of normal beta-Glc/ml of settled gel, respectively. The purified normal enzyme (14-18% yield) had a specific activity of 1.6 X 10(6) nmol/h/mg protein and was homogeneous as evidenced by a single protein species of Mr = 67,000 on sodium dodecylsulfate-polyacrylamide gel electrophoresis and reverse phase high-performance liquid chromatography (HPLC). Microsequencing demonstrated a single N terminus, and the sequence of the first 22 N-terminal amino acids was colinear with that predicted from the beta-Glc cDNA. Amino acid composition analyses of beta-Glc revealed a high content (35%) of hydrophobic amino acids. The N-decyl-deoxynojirimycin support facilitated the purification of the residual enzyme from type-1 AJGD spleen to about 7,500-fold in four steps with a yield of about 11%. These new affinity supports provided improved stability, capacity and/or specificity compared to other affinity or HPLC methods for purifying this lysosomal glycosidase.

Genetic heterogeneity in Gaucher disease: physicokinetic and immunologic studies of the residual enzyme in cultured fibroblasts from non-neuronopathic and neuronopathic patients

To elucidate the genetic heterogeneity in the three major phenotypic subtypes of Gaucher disease, the residual acid beta-glucosidase in fibroblasts from patients with all three subtypes from different ethnic and demographic groups was investigated by comparative kinetic, thermostability, and immunotitration studies. The kinetic studies delineated three distinct groups (designated A, B, and C) of residual activities with characteristic responses to the enzyme modifiers, taurocholate (or phosphatidylserine), and glucosyl sphingosine (or N-hexyl glucosyl sphingosine); Group A residual enzymes responded normally to these modifiers. All neuronopathic patients (types 2 and 3) and most non-Jewish, non-neuronopathic patients (type 1) had group A residual activities and thus could not be distinguished by their kinetic properties. Group B residual enzymes had markedly abnormal responses to these modifiers. All Ashkenazi and only two non-Jewish type 1 patients had group B residual activities. Group C residual activity had an intermediate response to all modifiers and represented a single Afrikaner type 1 patient. Pedigree studies indicated that this patient was a genetic compound for the group A (type 2) and group B (type 1) mutations. Thermostability studies showed additional heterogeneity of the residual activities within the three kinetic groups. Group A (type 2) and group B (type 1) enzymes had similarly decreased thermostabilities. In contrast, group A (type 1) residual activities were heterogeneous; three classes of thermostabilities were found among these enzymes: normal, decreased, and increased. Immunotitration of equal amounts of the normal or Gaucher disease beta-glucosidase activities with monospecific IgG indicated that the enzyme proteins from most Gaucher disease patients were antigenically altered and/or that large amounts of catalytically abnormal or inactive antigen were present. A decreased amount of antigenically and catalytically normal enzyme was present in a group A, type 1 African black patient, suggesting decreased stability or synthesis of his mutant acid beta-glucosidase. These kinetic, immunologic, and thermostability studies indicated that 1) type 1 Gaucher disease is biochemically heterogeneous and results from at least four distinct allelic acid beta-glucosidase mutations that alter enzyme structure and/or function, 2) neuronopathic and non-Jewish non-neuronopathic phenotypes cannot be distinguished reliably by kinetic analyses alone, and 3) the Ashkenazi type 1 Gaucher disease results from a unique mutation that alters a specific active site domain of acid beta-glucosidase.

Glycosphingolipid studies of visceral tissues and brain from type 1 Gaucher disease variants

Glucosylceramide and glucosylsphingosine isolated from spleen, liver and brain were quantitated and characterized in two unrelated patients with Gaucher disease, neither of whom had clinical or neuropathologic evidence of neuronal involvement. Visceral glucosylceramide accumulation did not differ in the two patients. Hepatic glucosylsphingosine content was 2-fold greater in a young severely affected 3-year-old American Black patient compared to that in a 56-year-old Ashkenazi Jewish patient. In contrast, significant differences in glycosphingolipid content and composition were observed in the brains of these two cases. Cerebral and cerebellar cortical glucosylceramide accumulated to a greater extent (3-fold) in the severely affected 3-year-old patient compared to that in the older case. The compositions of the acyl and sphingosyl base residues of glucosylceramide in the cerebral and cerebellar cortices from the Ashkenazi Jewish patient were similar to those in normal individuals. In comparison, the gray matter glucosylceramide in the severely affected patient had increased percentages of stearic acid (18:0) and eicosasphingenine (d20:1), suggesting that the accumulated substrate was derived from the brain ganglioside pool. Glucosylsphingosine was found in large amounts only in cerebral and cerebellar cortices from the severely affected patient. The glycolipid content and composition in this patient was similar to that found in the Norrbottnian (Type 3) form of Gaucher disease. The differences in glucosylceramide acyl and sphingosyl base composition in gray matter from the severely affected patient and that in the Ashkenazi Jewish patient suggested that the accumulated substrates were metabolized differently by the residual enzymes in each case.(ABSTRACT TRUNCATED AT 250 WORDS)

Gaucher disease types 1, 2, and 3: differential mutations of the acid beta-glucosidase active site identified with conduritol B epoxide derivatives and sphingosine

To elucidate the genetic heterogeneity in Gaucher disease, the residual beta-glucosidase in cultured fibroblasts from affected patients with each of the major phenotypes was investigated in vitro and/or in viable cells by inhibitor studies using the covalent catalytic site inhibitors, conduritol B epoxide or its bromo derivative, and the reversible cationic inhibitor, sphingosine. These studies delineated three distinct groups (designated A, B, and C) of residual activities with characteristic responses to these inhibitors. Group A residual enzymes had normal I50 values (i.e., the concentration of inhibitor that results in 50% inhibition) for the inhibitors and normal or nearly normal t1/2 values for conduritol B epoxide. All neuronopathic (types 2 and 3) and most non-Jewish nonneuronopathic (type 1) patients had group A residual activities and, thus, could not be distinguished by these inhibitor studies. Group B residual enzymes had about four- to fivefold increased I50 values for the inhibitors and similarly increased t1/2 values for conduritol B epoxide. All Ashkenazi Jewish type 1 and only two non-Jewish type 1 patients had group B residual activities. The differences in I50 values between groups A and B also were confirmed by determining the uninhibited enzyme activity after culturing the cells in the presence of bromo-conduritol B epoxide. Group C residual activity had intermediate I50 values for the inhibitors and represented a single Afrikaner type 1 patient: this patient was a genetic compound for the group A (type 2) and group B (type 1) mutations. These inhibition studies indicated that: Gaucher disease type 1 is biochemically heterogeneous, neuronopathic and non-Jewish nonneuronopathic phenotypes cannot be reliably distinguished by these inhibitor studies, and the Ashkenazi Jewish form of Gaucher disease type 1 results from a unique mutation in a specific active site domain of acid beta-glucosidase that leads to a defective enzyme with a decreased Vmax.

Use of activators and inhibitors to define the properties of the active site of normal and Gaucher disease lysosomal beta-glucosidase

Lysosomal beta-glucosidase ('glucocerebrosidase') in peripheral blood lymphocyte and spleen extracts from normal individuals and Ashkenazi-Jewish Gaucher disease type-1 patients were investigated using several modifiers of glucosyl ceramide hydrolysis. The negatively charged lipids, phosphatidylserine and taurocholate, had differential effects on the hydrolytic rates of the normal and Gaucher disease enzymes from either source. With the normal enzyme, either negatively charged lipid (up to 1 mmol/l) increased the reaction rates, while decreasing hydrolytic rates were obtained at greater concentrations. In comparison, the peak activities of the Gaucher enzymes were observed at about 2-3 mmol/l or 5-8 mmol/l of phosphatidylserine or taurocholate, respectively. These negatively charged lipids altered only the velocity of the reactions; the apparent Km values were not affected. Taurocholate or phosphatidylserine also facilitated the interaction of the normal enzyme with conduritol B epoxide, a covalent inhibitor of the catalytic site. Compared to the normal enzyme, the Ashkenazi-Jewish Gaucher type-1 enzyme required about 5-fold greater concentrations of conduritol B epoxide for 50% inhibition. Neutral or cationic acyl-beta-glucosides were found to be competitive or noncompetitive inhibitors of the enzymes, respectively. Alkyl beta-glucosides were competitive (or linear-mixed type) inhibitors of the normal splenic or lymphocyte enzyme with competitive inhibition constants (Ki) inversely related to the chain length. With octyl and dodecyl beta-glucoside nearly normal competitive Ki values were obtained with the splenic enzymes from Gaucher patients. These Ki values were not influenced by increasing phosphatidylserine or taurocholate concentrations. In contrast, the cationic lipids, sphingosyl-1-O-beta-D-glucoside (glucosyl sphingosine) and its N-hexyl derivative, were noncompetitive inhibitors whose apparent Ki values for the normal enzyme were 30 and 0.25 mumol/l, respectively. The Ki values for these sphingosyl glucosides were about increased 5 times for the Gaucher type-1 enzymes from Ashkenazi-Jewish Gaucher disease type-1 patients. The Ki values of glucosyl sphingosine for the normal or mutant enzymes were directly related to increasing concentrations of phosphatidylserine or taurocholate. This latter site appears to be specifically altered by a mutation in the structural gene for lysosomal beta-glucosidase in the Ashkenazi-Jewish form of type-1 Gaucher disease.

First-trimester prenatal diagnosis of Tay-Sachs disease

The prenatal diagnosis of Tay-Sachs disease was made in two at-risk fetuses by the analysis of chorionic villi obtained at 9 and 11 menstrual weeks, respectively. The diagnoses were based on the absence of beta-hexosaminidase A activity as determined by: (1) specific enzyme assays, (2) anion-exchange chromatography, and (3) cellulose acetate gel electrophoresis. The enzymatic diagnoses were confirmed on fetal tissue as well as by ultrastructural demonstration of the first-trimester fetal neuropathology. Optimal assay conditions for beta-hexosaminidase A in chorionic villi were established for the prenatal diagnosis of Tay-Sachs disease. Importantly, it was noted that a small amount of decidua or maternal blood could lead to misdiagnosis. Thus, extreme care must be taken in the preparation of chorionic villi for Tay-Sachs as well as other prenatal metabolic diagnoses.

Immune thrombocytopenia and Gaucher's disease

A 35-year-old Ashkenazi woman with Gaucher's disease was evaluated for persistent thrombocytopenia. The diagnosis of Gaucher's disease was made by bone marrow aspiration and confirmed by the determination of glucocerebrosidase levels in leukocytes and cultured skin fibroblasts. Studies of platelet-associated IgG and in vivo platelet survival demonstrated immune-mediated destruction of platelets consistent with immune thrombocytopenic purpura. A trial of prednisone had no effect on the platelet count. Total splenectomy resulted in a complete and prolonged remission. The clinical implications of Gaucher's disease and concurrent immune thrombocytopenic purpura are discussed.

Human lysosomal beta-glucosidase: purification by affinity chromatography

Two Sepharose-bound substrate analogs, 6'-aminohexanoyl-(2-N-sphingosyl-O-beta-D-glucoside) and 6'-aminohexyl-dodecanedioyl-1-(2-N-sphingosyl-1-O-beta-D-glu coside), were synthesized and used sequentially for the affinity purification of lysosomal beta-glucosidase (N-acyl-sphingosyl-1-O-beta-D-glucoside:glucohydrolase, EC 3.2.1.45). The capacities of these nondegradable affinity supports were 0.1 and 0.15 mg enzyme/ml settled gel, respectively. The purified enzyme had a specific activity of 75 mumol min-1 mg-1. The preparation had a single protein band with a molecular weight of 67,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, evidencing its apparent homogeneity. Isoelectric focusing on granular gels revealed four molecular forms of the enzyme with pI values of 4.0, 4.5, 4.7, and 5.8 to 6.2. The purified enzyme hydrolyzed glucosyl ceramide and 4-methylumbelliferyl-beta-D-glucoside with Km and Vmax values of 0.6 and 2.5 mM, and 101 and 26.1 mumol min-1 mg-1, respectively. The enzyme also hydrolyzed octyl beta-glucoside, a linear mixed-type inhibitor of the enzyme. Binding constants (Ki) were determined for the inhibitors, sphingosyl-1-O-beta-D-glucoside (Ki = 20 microM) and its N-hexyl derivative (Ki = 0.3 microM). The enzyme had a half-life of 65 and 30 min at 50 degrees C and pH 5.0 or 6.0, respectively. In addition, two other classes of ligands were used for the purification of lysosomal beta-glucosidase, and their capacities and specificities were compared to those of the substrate analog affinity supports. These included (i) the alkyl amine inhibitors octylamine, decylamine, and tetradecylamine; and (ii) the inhibitors, 6-aminohexanoyl-beta-glucosylamine and aminododecanoyl-1-(2-N-sphingosyl-1-O-beta-D-glucoside). Compared to these other ligand columns, the substrate analog affinity supports had about 100- to 1000-fold greater capacities or afforded 8- to 40-fold greater purification of human lysosomal beta-glucosidase.

Reduced plasma concentrations of total, low density lipoprotein and high density lipoprotein cholesterol in patients with Gaucher type I disease

Plasma lipid and serum apoprotein concentrations were determined in twenty-nine individuals with Gaucher type I disease. Plasma total cholesterol, low density lipoprotein (LDL) cholesterol and high density lipoprotein (HDL) cholesterol were all significantly reduced in the patients with Gaucher disease compared to a group of matched control subjects. Total, LDL and HDL cholesterol were lower in males than in females with Gaucher disease. These sex differences appeared to be inversely correlated with the severity of disease manifestations which were greater in the males. Serum levels of apoprotein-B and apoprotein-AI, the major structural apoproteins of LDL and HDL, respectively, were decreased in the subjects with Gaucher disease. Thus, the reductions in LDL and HDL cholesterol were associated with reduced numbers of lipoprotein particles in plasma. In contrast, apoprotein-E, a protein which is secreted by several tissues, including activated macrophages and which may mediate hepatic catabolism of lipoproteins, was elevated in the patients. Since macrophages may also catabolize lipoproteins, Gaucher disease may serve as a model for the effect of activated macrophages upon human lipoprotein metabolism.

Human lysosomal beta-glucosidase: kinetic characterization of the catalytic, aglycon, and hydrophobic binding sites

Three binding sites on highly purified lysosomal beta-glucosidase from human placenta were identified by studies of the effects of interactions of various enzyme modifiers. The negatively charged lipids, taurocholate and phosphatidylserine, were shown to be noncompetitive, nonessential activators of 4-methylumbelliferyl-beta-D-glucoside hydrolysis. Similar results were observed using the natural substrate, glucosyl ceramide, and low concentrations of taurocholate (less than 1.8 mM) or phosphatidylserine (0.5 mM). However, higher concentrations resulted in a complex partial inhibition of glucosyl ceramide hydrolysis. Increasing concentrations of phosphatidylserine obviated the effects of taurocholate, suggesting that these compounds compete for a common binding site on the enzyme. Glucosyl sphingosine and its N-hexyl derivative were potent noncompetitive inhibitors of the enzyme activity using either substrate. Taurocholate (or phosphatidylserine) and glucosyl sphingosine were shown to be mutually exclusive, indicating competition for a common binding site. In contrast, octyl- and dodecyl-beta-glucosides were linear-mixed-type inhibitors of glucosyl ceramide or 4-methylumbelliferyl-beta-D-glucoside hydrolysis, indicating at least two binding sites on the enzyme. Inhibition by these alkyl beta-glucosides was observed only in the presence of taurocholate or phosphatidylserine. The competitive component [Ki (slope)] for the two alkyl beta-glucosides decreased with increasing alkyl chain length, and was unaffected by increasing taurocholate or phosphatidylserine concentration. The noncompetitive component [Ki (intercept)] was nearly identical for both alkyl beta-glucosides and was decreased by increasing taurocholate or phosphatidylserine concentration. These results indicated that the negatively charged lipids and alkyl beta-glucosides were not mutually exclusive, but interacted with different binding sites on the enzyme. Gluconolactone was shown to protect the enzyme from inhibition by the catalytic site-directed covalent inhibitor, conduritol B indicating an interaction at a common binding site. In the presence of substrate, taurocholate facilitated the inhibition of gluconolactone or conduritol B epoxide. These studies indicated that lysosomal beta-glucosidase had at least three binding sites: (i) a catalytic site which cleaves the beta-glucosidic moiety, (ii) an aglycon site which binds the acyl or alkyl moieties of substrates and some inhibitors, and (iii) a hydrophobic site which interacts with negatively charged lipids and facilitates enzyme catalysis.

Synthesis of a fluorescent derivative of glucosyl ceramide for the sensitive determination of glucocerebrosidase activity

A fluorescent derivative of glucosyl ceramide was synthesized by covalently linking a fluorescent fatty acid, 12-[N-methyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)] aminododecanoic acid to the amino group of sphingosyl-1-O-beta-D-glucoside, glucosyl sphingosine. For hydrolysis by glucocerebrosidase, this substrate was dispersed in mixed micelles with Triton X-100 and sodium taurocholate or in unilamellar liposomes with phosphatidylcholine and the negatively charged lipid, dicetylphosphate. In either micellar or liposomal dispersions of the fluorescent substrate, reaction rates were linear with time and protein concentration, and saturation kinetics were observed. The rate of hydrolysis of this fluorescent substrate was equal to that obtained with radiolabeled glucosyl ceramide. The fluorescent glucosyl ceramide was used to determine glucocerebrosidase activity in extracts of human leukocytes, cultured skin fibroblasts, and various tissues as well as in partially purified splenic and placental glucocerebrosidase preparations. This fluorescent derivative of the natural substrate was not hydrolyzed by aryl beta-glucosidase(s), thereby facilitating the specific and reliable diagnosis of heterozygotes and homozygotes with Gaucher disease.

Silicon nephropathy mimicking Fabry's disease

Percutaneous renal biopsy was performed in a surface coal miner with radiographic and histopathologic pulmonary changes consistent with acute silicolipoproteinosis who developed proteinuria and hematuria. Electron microscopic evaluation of the renal tissue specimen revealed a diffusely thickened glomerular basement membrane, foot process effacement, and dense lamellar inclusions in swollen glomerular epithelial cells, similar to those seen in Fabry's disease. However, normal levels of plasma alpha-galactosidase A, normal urinary sediment glycosphingolipids and the absence of the clinical characteristics of Fabry's disease excluded this diagnosis. This case illustrates that electron-dense lamellar inclusions, similar to those seen in Fabry's disease, may be seen in other entities such as nephropathy associated with silicosis.

Gaucher type I (Ashkenazi) disease: a new method for heterozygote detection using a novel fluorescent natural substrate

A new acid beta-glucosidase assay for the detection of heterozygotes for Gaucher Type I disease has been developed using isolated lymphocytes as enzyme source and a novel fluorescent natural substrate, NBD-glucosyl ceramide. The procedure for optimal heterozygote discrimination was established by systematic evaluation of the effect of various solubilization techniques, detergent concentrations, pH, enzyme sources and artificial vs. natural substrates. A pilot screening study indicated the feasible application of this assay for heterozygote detection in the high-risk Ashkenazi Jewish population.

Oculomotor abnormalities in chronic GM2 gangliosidosis

The clinical and electro-oculographic eye abnormalities in chronic GM2 gangliosidosis have been described. The most prominent oculomotor disturbances in our patients involved the pursuit system. This was evident during performance of eye tracking and vestibulo-ocular reflex suppression. Saccadic eye movements were dysmetric but were normal in velocity. These findings point to disturbances of cerebellar oculomotor control. While the oculomotor defects are nonspecific in this chronic form of beta-hexosaminidase A deficiency, they broaden the spectrum of clinical features considered to be typical ocular manifestations in many storage diseases. Disturbances in the oculomotor system may be the only ocular sign of chronic GM2 gangliosidosis.

Chronic GM2 gangliosidosis masquerading as atypical Friedreich ataxia: clinical, morphologic, and biochemical studies of nine cases

A progressive spinocerebellar degenerative disorder was characterized in nine patients, aged 11 to 37 years, from four unrelated Ashkenazi Jewish families; affected individuals had markedly deficient beta-hexosaminidase A activity. Symptoms included early onset of cerebellar signs (tremor, incoordination, and dysarthia) and, with maturity, the development of upper and lower motor neuron disorders, marked dysarthia, and ataxia. Three older patients, aged 26, 32, and 37 years, had dementia or recurrent psychotic episodes. Membrane-bound lamellar cytoplasmic inclusions, consistent with lysosomal ganglioside accumulation, were observed in rectal ganglia. The activity of beta-hexosaminidase A was markedly deficient in all sources analyzed. Parents had activities consistent with heterozygosity, confirming autosomal-recessive transmission of the beta-hexosaminidase A-deficient gene and the adult variant disorder. Residual beta-hexosaminidase A activity, partially purified by anion-exchange chromatography from cultured skin fibroblasts of the affected individuals, was heat-labile and co-electrophoresed with normal beta-hexosaminidase A. These findings suggest that these patients were allelic for a new beta-hexosaminidase A mutation and may represent a genetic compound of this allele and the allele causing Tay-Sachs disease.

The M-mode echocardiogram in Fabry's disease

Fabry's disease results from deficient activity of the enzyme alpha-galactosidase A. Cardiac abnormalities result from glycosphingolipid deposition in the myocardium, valvular tissue, and vessel walls. A noninvasive method to examine these abnormalities would be useful in the evaluation of patients. We examined the echocardiograms of 32 patients, 25 hemizygous and seven heterozygous, for Fabry's disease. The aortic root diameter was measured in each hemizygote. In nine patients under 26 years it was 33.2 +/- 1.2 mm. and in two it was dilated. In 16 patients over 26 years it was 38.8 +/- 1.2 mm. (p < 0.01), and in 12 it was dilated. The left ventricular posterior wall was measured in the echocardiogram of 21 normotensive hemizygotes. The difference in thickness between nine patients under 26 years (9.6 +/- 1.3 mm.) and 12 patients over 26 years (12.4 +/- .07 mm.) was not statistically significant. Only two of the nine younger patients had left ventricular wall thickness greater than normal compared to eight of the 12 older patients. The mean left ventricular shortening fraction of 22 hemizygous patients was normal. One hemizygote had echocardiographic evidence of mitral valve prolapse. Four of the seven heterozygotes had normal echocardiograms. Among the other three, one had increased left ventricular wall thickness, a second had disproportionate ventricular septal thickness, and a third had both abnormalities. The echocardiographic aortic root size was normal in each heterozygote. Abnormal echocardiographic findings were more common in older hemizygous patients, a distribution similar to that of the age of onset of cardiac dysfunction. Increased left ventricular wall thickness probably reflects glycosphingolipid deposition in the myocardium. Dilatation of the aortic root may result from degenerative changes of the aortic media. Abnormalities of mitral valve echoes were uncommon.

Comparative physical, kinetic and immunologic properties of the acidic and neutral alpha-D-mannosidase isozymes from human liver

Human alpha-mannosidases A, B and C were partially purified from liver by conventional and affinity chromatographic procedures. The kinetic, physical and immunologic properties of the A, B and C isozymes were determined including pH optima, Km, effects of various inhibitors and activators, thermal stabilities, electrophoretic mobilities, native molecular weights and antigenic relationships. By gel filtration, the apparent native molecular weights were 240,000, 300,000 and 420,000 for the A, B and C isozymes, respectively. By polyacrylamide gel electrophoresis, the A and B isozymes had native molecular weights of approximately 150,000 and appeared to be charge isomers. Antibodies to the purified A and B isozymes were produced; cross-reactivity between the A and B isozymes against anti-A and anti-B immune sera were observed by double immunodiffusion and immunoprecipitation. In contrast, no reactivity of the C isozyme was detected with either immune serum. Based on these studies, models are presented for the molecular interrelationship of alpha-mannosidases A and B.

Mannosidosis: clinical, morphologic, immunologic, and biochemical studies

The primary metabolic defect in mannosidosis is the deficiency of the acidic alpha-mannosidase A and B activites which results in the lysosomal accumulation of mannose-rich substrates. Out studies demonstrate that the enzymatic diagnosis of suspect homozygotes can be made reliably using plasma, isolated leukocytes, or cultured skin fibroblasts assayed carefully at the appropriate acidic pH. Immunologic studies of a mannosidosis homozygote revealed significant abnormalities of neutrophil function; these included a depressed chemotactic responsiveness and impaired phagocytosis of bacteria. Lymphocyte transformation studies showed a 20% of normal response to purified phytohemagglutinin and a 25% of normal response to concanavalin A. Three major components of alpha-mannosidase activity in normal human liver were resolved by ion exchange chromatography on DEAE-cellulose and electrophoresis on cellulose acetate gels. Electrophoresis of the liver extract from homozygote I with mannosidosis revealed only one band of activity which coelectrophoresed with the alpha-mannosidase C isozyme partially purified from normal liver. However, ion exchange chromatography revealed the presence of residual hepatic acidic activities; the residual A isozyme was eluted in a position corresponding to that of normal alpha-mannosidase A whereas the residual B activity was eluted at a slightly more electronegative position than that of normal B isozyme. The apparent Km values for alpha-mannosidase activity as determined from Linweaver-burk plots were 1.1 mM for normal liver and 0.9 mM for normal leukocytes. In contrast, the residual activity in these sources from homozygote 1 could not be saturated within the solubility range of the substrate; the apparent Km value was estimated at 15.4 mM in liver extracts. Zinc significantly lowered the apparent Km value of the acidic activity in normal liver (from 1.2 to 0.24 mM), whereas this metallic ion had little effect on the values for mannosidosis hepatic activity (from 15.4 to 12.3 mM). Unlike zinc, cobalt had its major effect on the acidic activity in the mannosidosis liver extract, lowering the apparent Km from 15.4 to 3.9 mM, whereas the apparent Km for the normal activity was increased from 1.2 to 1.9 mM. The residual acidic activities were markedly stimulated by zinc in both leukocytes (approximately 300%) and plasma ( approximately 400%) from the homozygotes and to a lesser extent in those sources from normal individuals. In contrast, cobalt enhanced the residual acidic activities in leukocytes (approximately 500%) and plasma (approximately 200%) from the homozygotes while inhibiting these acidic activities (78.9% and 47.7%, respectively) in normal individuals.

Evidence for carrier proteins in bile acid synthesis. The effect of squalene and sterol carrier protein and albumin on the activity of 12alpha-hydroxylase

The possibility that carrier proteins are involved in bile acid synthesis was investigated using rat liver homogenates. The 105 000 X g supernatant fraction was found to contain heat stable proteins that bound the bile acid precursor, 7alpha-hydroxy-4-cholesten-3-one, and increased the amount of 7alpha, 12alpha-dihydroxy-4-cholesten-3-one formed by the microsomal enzyme, 12alpha-hydroxylase. Subsequent studies were carried out to determine if squalene and sterol carrier protein or albumin, two lipid binding proteins present in the 105 00 X g supernatant fraction of rat liver homogenates, may be responsible for the effects seen with this fraction. Squalene and sterol carrier protein bound several water insoluble bile acid precursors, including 7alpha-hydroxy-4-cholesten-3-one, and increased the apparent activity of 12alpha-hydroxylase. Squalene and sterol carrier protein, however, did not bind either cholic acid or chenodeoxycholic acid. Rat serum albumin also bound 7alpha-hydroxy-4-cholesten-3-one and increased the apparent activity of 12alpha-hydroxylase. Kinetic analysis indicated that the apparent stimulation of 12alpha-hydroxylase by squalene and sterol carrier protein and albumin was due to increased solubilization of the substrate, 7alpha-hydroxy-4-cholesten-3-one. Thus, these studies indicate that bile acid precursor carrier proteins are present in the 105 000 Xg supernatant fraction of rat liver homogenates and suggest that squalene and sterol carrier protein or albumin may participate as carrier proteins in bile acid synthesis.