Human β-glucuronidase: Assignment of the structural gene to chromosome 7 using somatic cell hybrids

-Glucuronidase (GUS) has become an important enzyme model for the genetic study of molecular disease, enzyme realization, and therapy, and for the biogenesis and function of the lysosome and lysosomal enzymes. The genetics of human -glucuronidase was investigated utilizing 188 primary man-mouse and man-Chinese hamster somatic cell hybrids segregating human chromosomes. Cell hybrids were derived from 16 different fusion experiments involving cells from ten different and unrelated individuals and six different rodent cell lines. The genetic relationship of GUS to 28 enzyme markers representing 19 linkage groups was determined, and chromosome studies on selected cell hybrids were performed. The evidence indicates that the -glucuronidase gene is assigned to chromosome 7 in man. Comparative linkage data in man and mouse indicate that the structural gene GUS is located in a region on chromosome 7 that has remained conserved during evolution. Involvement of other chromosomes whose genes may be important in the final expression of GUS was not observed. A tetrameric structure of human -glucuronidase was demonstrated by the formation of three heteropolymers migrating between the human and mouse molecular forms in chromosome 7 positive cell hybrids. Linkage of GUS to other lysosomal enzyme genes was investigated. -Hexosaminidase HEX _B) was assigned to chromosome 5; acid phosphatase₂ (ACP ₂) and esterase A₄ (ES-A ₄) were assigned to chromosome 11; HEX _A was not linked to GUS; and -galactosidase (-GAL) was localized on the X chromosome. These assignments are consistent with previous reports. Evidence was not obtained for a cluster of lysosomal enzyme structural genes. In demonstrating that GUS was not assigned to chromosome 9 utilizing an X/9 translocation segregating in cell hybrids, the gene coding for human adenylate kinase₁ was confirmed to be located on chromosome 9.Supported by NIH Grants HD 05196, GM 20454, and GM 06321, by NSF Grant BMS 73-07072, and by HEW Maternal and Child Health Service, Project 417.     

The UPS locus encoding uroporphyrinogen I synthase is located on human chromosome 11

The expression of the UPS locus encoding uroporphyrinogen I synthase has been investigated in human/mouse somatic cell hybrids. Human and mouse uroporphyrinogen I synthase can be readily distinguished by their isoelectric points. In hybrid cells, both human and mouse isozymes are detected. The multiple human uroporphyrinogen I synthase isozymes segregate as a single unit, as expected if they are the products of a single locus. The absence of new heteropolymers in hybrid cells supports the biochemical evidence that the active enzyme is a monomer. The presence of human uroporphyrinogen I synthase in hybrid clones was correlated with the presence of human chromosome 11, or its enzymatic marker, without exception in 44 independent hybrid lines. All other chromosomes could be eliminated as possible locations for this locus, due to their independent segregation. This report represents the first gene assignment for an enzyme in the heme biosynthesis pathway.     

Isolation and identification of some guanidino compounds in the urine of patients with hyperargininaemia by liquid chromatography,thin-layer chromatography and gas chromatography-mass spectrometry

Liquid column chromatographic studies of monosubstituted guanidino compounds, which are excreted in the urine of patients with hyperargininaemia are reported. The guanidino-positive peaks, with the highest excretion values, were isolated from urine and the isolated compounds were identified by thin-layer chromatography and gas chromatography—mass spectrometry. Guanidinoacetic acid, N-α-acetylarginine, argininic acid, γ-guanidinobutyric acid, arginine and α-keto-δ-guanidinovaleric acid were found to be excreted at high levels in the urine of patients with hyperargininaemia compared with controls.     

The absorption of protons with alpha-methyl glucoside and alpha-thioethyl glucoside by the yeast N.C.Y.C. 240. Evidence against the phosphorylation hypothesis.

1. When yeast N.C.Y.C. 240 was grown with maltose in a complex medium based on yeast extract and peptone, washed cell preparations fermented alpha-methyl glucoside much more slowly than maltose. 2. The yeast absorbed alpha-methyl[14C]glucoside from a 10mM solution in the presence of antimycin and iodoacetamide, producing [14C]glucose, which accumulated outside the cells. The yeast itself contained hexose phosphates, trehalose, alpha-methyl glucoside and other products labelled with 14C, but no alpha-methyl glucoside phosphate. 3. About 1 equiv. of protons was absorbed with each equivalent of alpha-methylglucoside, and 1 equiv. of K+ ions left the yeast. 4. alpha-Thioethyl glucoside was also absorbed along with protons. Studies by g.l.c. showed that the yeast concentrated the compound without metabolizing it. 5. The presence of trehalose, sucrose, maltose, L-sorbose, glucose or alpha-phenyl glucoside in each case immediately stimulated proton uptake, whereas fructose, 3-O-methylglucose and 2-deoxyglucose failed to do so. 6. The observations support the conclusion that alpha-thioethyl glucoside, alpha-methyl glucoside and maltose are substrates of one or more proton symports, whereas they seem inconsistent with the notion that the absorption of alpha-methyl glucoside involves the phosphorylation of the carbohydrate [Van Stevenick (1970) Biochim. Biophys. Acta 203, 376-384].     

The effects of ionophores on the fluorescence of the cation 3,3''-dipropyloxadicarbocyanine in the presence of pigeon erythrocytes, erythrocyte ''ghosts'' or liposomes.

1. Pigeon erythrocytes, resealed lysed erythrocytes or liposomes derived from erythrocyte lipids were suspended in solutions containing up to 2 micrometer-3,3'-dipropyloxadicarbocyanine iodide. Gramicidin, valinomycin, nigericin or carbonyl cyanide p-trifluoromethoxy-phenylhydrazone, or combinations of these, were used to induce electrical diffusion potentials dependent on Na+, K+ or protons. In each instance hyperpolarization of the cell membrane lowered the fluorescence of the cell suspension, a process that was completed in about 1 min. Subsequent depolarization caused an increase in fluorescence. 2. Quenching of the fluorescence of the cell suspension appeared to be due to the reversible binding of the dye to the cells. Much larger amounts of dye were bound, both to the intact and to the resealed erythrocytes, than would be expected if partitioning of the dye cation followed the Nernst equation. The dependence of the binding on the extracellular dye concentration was studied in the presence and absence of valinomycin. The results were consistent with the suggestion of Sims, Waggoner, Wang & Hoffman [(1974) Biochemistry 13, 3315-3330] that the dye was bound at both membrane surfaces and that, at low dye concentrations, hyperpolarizing the cells promoted dye binding at the inner membrane surface. 3. The applications of the technique are limited by the circumstance that the direct effect of the electric field on the uptake of the dye into the cells is amplified by a binding process that may be affected by other physiological variables.     

Sequencing and expression of the Butyrivibrio fibrisolvens xylB gene encoding a novel bifunctional protein with beta-D-xylosidase and alpha-L-arabinofuranosidase activities.

A single gene (xylB) encoding both beta-D-xylosidase (EC 3.2.1.37) and alpha-L-arabinofuranosidase (EC 3.2.1.55) activities was identified and sequenced from the ruminal bacterium Butyrivibrio fibrisolvens. The xylB gene consists of a 1.551-bp open reading frame (ORF) encoding 517 amino acids. A subclone containing a 1.843-bp DNA fragment retained both enzymatic activities. Insertion of a 10-bp NotI linker into the EcoRV site within the central region of this ORF abolished both activities. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of cytoplasmic proteins from recombinant Escherichia coli confirmed the presence of a 60,000-molecular-weight protein in active subclones and the absence of this protein in subclones lacking activity. With p-nitrophenyl-beta-D-xylopyranoside and p-nitrophenyl-alpha-L-arabinofuranoside as substrates, the specific activity of arabinosidase was found to be approximately 1.6-fold higher than that of xylosidase. The deduced amino acid sequence of the xylB gene product did not exhibit a high degree of identity with other xylan-degrading enzymes or glycosidases. The xylB gene was located between two incomplete ORFs within the 4,200-bp region which was sequenced. No sequences resembling terminators were found within this region, and these three genes are proposed to be part of a single operon. Based on comparison with other glycosidases, a conserved region was identified in the carboxyl end of the translated xylB gene which is similar to that of glucoamylase from Aspergillus niger.     

Regional assignment of two genes of the human branched-chain alpha-keto acid dehydrogenase complex: the E1 beta gene (BCKDHB) to chromosome 6p21-22 and the E2 gene (DBT) to chromosome 1p31

Maple syrup urine disease (MSUD) is caused by the deficiency of the mitochondrial branched-chain alpha-keto acid dehydrogenase complex. The multienzyme complex is a macromolecule (Mr 4 X 10(6] consisting of at least six distinct subunits. In this study, the human E1 beta gene (BCKDHB) has been localized to human chromosome 6 by hybrid somatic cell analysis, and regionally assigned to chromosome bands 6p21-22 by in situ hybridization. The E2 gene (DBT), which was previously localized to chromosome 1, is regionally assigned to the chromosome band 1p31 also by in situ hybridization. Localization of the E1 beta gene to chromosome 6p21-22 assigns another major human disease locus to a region that contains several important genes, including the major histocompatability complex, tumor necrosis factor, and heat-shock protein HSP70. Mapping of the E1 beta and the E2 genes may provide information for the linkage analysis of MSUD families with mutations in these two loci.     

Cloning of human heparan sulfate proteoglycan core protein, assignment of the gene (HSPG2) to 1p36.1----p35 and identification of a BamHI restriction fragment length polymorphism.

We have isolated a cDNA coding for the core protein of the large basement membrane heparan sulfate proteoglycan (HSPG) from a human fibrosarcoma cell (HT1080) library. The library was screened with a mouse cDNA probe and one clone obtained, with a 1.5-kb insert, was isolated and sequenced. The sequence contained an open reading frame coding for 507 amino acid residues with a 84% identity to the corresponding mouse sequence. This amino acid sequence contained several cysteine-rich internal repeats similar to those found in component chains of laminin. The HSPG cDNA clone was used to assign the gene (HSPG2) to the p36.1----p35 region of chromosome 1 using both somatic cell hybrid and in situ hybridization. In the study of the polymorphisms of the locus, a BamHI restriction fragment length polymorphism was identified in the gene. This polymorphism displayed bands of 23 and 12 kb with allele frequencies of 76 and 24%, respectively.