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L Toma

Publications and source records attributed to L Toma.

At least 55 records · Page 3Linked to original sources
PubMed1996

Transport of UDP-galactose into the Golgi lumen regulates the biosynthesis of proteoglycans.

The lumen of the Golgi apparatus is the subcellular site where galactose is transferred, from UDP-galactose, to the oligosaccharide chains of glycoproteins, glycolipids, and proteoglycans. The nucleotide sugar, which is synthesized in the cytosol, must first be transported into the Golgi lumen by a specific UDP-galactose transporter. Previously, a mutant polarized epithelial cell (MDCKII-RCAr) with a 2% residual rate of transport of UDP-galactose into the lumen of Golgi vesicles was described (Brandli, A. W., Hansson, G. C., Rodriguez-Boulan, E., and Simons, K. (1988) J. Biol. Chem. 263, 16283-16290). The mutant has an enrichment in glucosyl ceramide and cell surface glycoconjugates bearing terminal N-acetylglucosamine, as well as a 75% reduction in sialylation of cell surface glycoproteins and glycosphingolipids. We have now studied the biosynthesis of galactose containing proteoglycans in this mutant and the corresponding parental cell line. Wild-type Madin-Darby canine kidney cells synthesize significant amounts of chondroitin sulfate, heparan sulfate, and keratan sulfate, while the above mutant synthesizes chondroitin sulfate and heparan sulfate but not keratan sulfate, the only proteoglycan containing galactose in its glycosaminoglycan polymer. The mutant also synthesizes chondroitin 6-sulfate rather than only chondroitin 4-sulfate as wild-type cells. Together, the above results demonstrate that the Golgi membrane UDP-galactose transporter is rate-limiting in the supply of UDP-galactose into the Golgi lumen; this in turn results in selective galactosylation of macromolecules. Apparently, the Km for galactosyltransferases involved in the synthesis of linkage regions of heparan sulfate and chondroitin sulfate are significantly lower than those participating in the synthesis of keratan sulfate polymer, glycoproteins, and glycolipids. The results also suggest that the 6-O-sulfotransferases, in the absence of their natural substrates (keratan sulfate) may catalyze the sulfation of chondroitin 4-sulfate as alternative substrate.

Animals↗
PubMed1996

Contact interactions method: a new algorithm for protein folding simulations.

Computer simulations of simple exact lattice models are an aid in the study of protein folding process; they have sometimes resulted in predictions experimentally proved. The contact interactions (CI) method is here proposed as a new algorithm for the conformational search in the low-energy regions of protein chains modeled as copolymers of hydrophobic and polar monomers configured as self-avoiding walks on square or cubic lattices. It may be regarded as an extension of the standard Monte Carlo method improved by the concept of cooperativity deriving from nonlocal contact interactions. A major difference with respect to other algorithms is that criteria for the acceptance of new conformations generated during the simulations are not based on the energy of the entire molecule, but cooling factors associated with each residue define regions of the model protein with higher or lower mobility. Nine sequences of length ranging from 20 to 64 residues were used on the square lattice and 15 sequences of length ranging from 46 to 136 residues were used on the cubic lattice. The CI algorithm proved very efficient both in two and three dimensions, and allowed us to localize energy minima not localized by other searching algorithms described in the literature. Use of this algorithm is not limited to the conformational search, because it allows the exploration of thermodynamic and kinetic behavior of model protein chains.

Algorithms↗
PubMed1996

Differences in the nonreducing ends of heparan sulfates excreted by patients with mucopolysaccharidoses revealed by bacterial heparitinases: a new tool for structural studies and differential diagnosis of Sanfilippo's and Hunter's syndromes.

Enzymatic and chemical analyses of the structures of heparan sulfates excreted in the urine by patients with Sanfilippo's and Hunter's syndromes revealed that their nonreducing ends differ from each other and reflect the enzyme deficiency of the syndromes. The heparan sulfates from the different syndromes were treated with heparitinase II, crude enzyme extracts from Flavobacterium heparinum, and nitrous acid degradation. The heparan sulfates from patients with Sanfilippo A (deficient in heparan N-sulfatase) and Sanfilippo B (deficient in alpha-N-acetylglucosaminidase) were degraded with heparitinase II producing, besides unsaturated disaccharides, substantial amounts of glucosamine N-sulfate and N-acetylglucosamine, respectively. The heparan sulfate from patients with Hunter's syndrome (deficient in iduronate sulfatase) were degraded by heparitinase II or crude enzyme extracts to several products, including two saturated disaccharides containing a sulfated uronic acid at their nonreducing ends. The heparan sulfate from patients with Sanfilippo's C syndrome (deficient in acetyl Co-A: alpha-glucosaminide acetyltransferase) produced, by action of heparitinase II, among other products, two sulfated trisaccharides containing glucosamine with a nonsubstituted amino group. In addition to providing a new tool for the differential diagnosis of the mucopolysaccharidoses, these results bring new insights into the specificity of the heparitinases from Flavobacterium heparinum.

Biomarkers↗
PubMed1994

Biotin and biotin analogues specifically modify the fluorescence decay of avidin.

Avidin, a basic tetrameric glycoprotein, isolated from hen egg-white, binds up to four molecules of biotin with exceptionally high affinity. The presence of tryptophanyl residues in the active site pointed out the opportunity of correlating the protein fluorescence with biotin binding. We have performed both steady state and dynamic fluorescence experiments using biotin or biotin-derived molecules (biotinamine, diaminobiotin and iminobiotin) as ligands. The fluorescence decay data can only be fitted by two continuous distributions of lifetimes which may reflect the presence of static or dynamic microheterogeneity in the environment of the tryptophan residues. We observed that the binding of biotin, biotinamine and iminobiotin reduces the widths of both distributions to discrete lifetimes thus indicating a more homogenous environment for the emitting tryptophan residues. Instead, the binding of diaminobiotin, which lacks the imidazolone ring, affects one lifetime distribution only. The binding of biotin also affects the rotational correlation time of avidin, which becomes shorter, suggesting a more compact structure of the ligated protein. The utility of analyzing the fluorescence in terms of distributions appears to be further warranted.

Animals↗
PubMed1993

Enzymic acylation of methyl D- and L-glycopyranosides: influence of the 3-hydroxyl group.

Porcine pancreatic (PPL), Candida cylindracea (CCL) and Pseudomonas cepacia (LPS) lipases, suspended in organic solvents, were used to regioselectively acylate methyl 6-O-butyryl-alpha-D- and L-allopyranosides and methyl 6-O-butyryl-3-deoxy-alpha-D- and L-ribo-hexopyranosides. Both the D- and the L-3-deoxy sugars showed a complete regioselectivity, while the reactions of the allosides proved to be less regioselective. This indicates that the presence of the hydroxyl group at C-3 is an unfavourable factor for the action of the lipases.

Acylation↗
PubMed1992

Conformational studies of muscarone analogues: X-ray analysis and molecular mechanics calculations.

The X-ray structure of muscarone analogues 3 and 4 was determined and compared with that of muscarone (1, iodide and picrate salts), muscarine 2, dioxolane 5, oxathiolane 6, and tetrahydrofuran 7. In order to better define the pharmacological stereoselectivity of muscarone, the conformational profiles of compounds 1, 2, 3, and 5 were analyzed using Allinger's MM2(85) program or, in the case of 4, by 1H NMR spectroscopy. The conformation of the ring in 1 proved similar to that of the other derivatives. MM2 calculations predicted a preferred gauche arrangement of the side chain for 1 and its analogues; such an arrangement was also observed in the solid state of muscarone picrate. Thus, the antiperiplanar arrangement reported for crystalline muscarone iodide appears to be due to crystallographic packing forces. As a consequence, the rationalization of the pharmacological profile of 1 based on the antiperiplanar arrangement is now highly questionable. The lack of stereoselectivity of 4 can be attributed to the absence of a stereocenter at C-2 whereas, in our opinion, there are currently no sound explanations for the low values of eudismic ratios for the muscarone enantiomers.

Molecular Conformation↗
PubMed1992

T-lymphocyte reactivity to the recombinant mycobacterial 65- and 70-kDa heat shock proteins in multiple sclerosis.

Owing to their conservation and immunogenicity, heat shock proteins (hsps) represent a class of potential autoantigens. Moreover, they could be targets for gamma delta T lymphocytes, which are prominent in various immune disorders. We studied the T cell proliferative primary responses to recombinant M. bovis 65 kDa hsp (hsp65) and M. tuberculosis 70 kDa hsp (hsp70) in 31 patients with multiple sclerosis (MS), 19 patients with other neurological diseases (OND) and 19 healthy individuals. Positive responses to hsp70, but not to hsp65 were significantly more frequent in patients with MS than in patients with OND or in healthy individuals. In order to verify and refine these results and to characterize the hsp reactive T lymphocytes, we screened 147 PPD-specific long-term T cell lines (76 from 10 patients with MS and 71 from 12 healthy donors) for their proliferative response to hsp65 and hsp70. hsp70-reactive T lines were significantly more common in patients with MS than in healthy controls. The number of T lines responding to hsp65 increased in the MS group only slightly. In 19 T lymphocyte lines from patients with MS and healthy donors, a cytofluorometric analysis was performed with special attention paid to distinct T cell receptor gamma delta determinants. With one exception, in each line the population of gamma delta T cells remained a minority. We conclude that an increased T cell response to mycobacterial hsp70 may be present in patients with multiple sclerosis.

Adolescent↗
PubMed1992

Tumour necrosis factor-alpha synthesis by cerebrospinal-fluid-derived T cell clones from patients with multiple sclerosis.

T-cell clones derived from the CSF (cerebrospinal fluid) of MS (multiple sclerosis) patients have been analysed for the production of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-2 (IL-2) and interleukin-4 (IL-4). Each CSF-T clone (both CD4+ and CD8+) produced substantial amounts of IFN-gamma and especially TNF-alpha compared with autologous peripheral T clones and liver-infiltrating T clones from patients with chronic active hepatitis. The large quantities of TNF produced by CSF-T cell clones suggest an important role for this cytokine in MS immunopathogenesis.

Adult↗
PubMed1990

Impaired sulphated glycosaminoglycan metabolism in a patient with GM-2 gangliosidosis (Tay-Sachs disease).

An abnormal urinary excretion of sulphated glycosaminoglycans in a patient with GM-2 gangliosidosis (Tay-Sachs disease) is described. Besides the accumulation of GM-2 ganglioside in liver and lack of hexosaminidase A, the patient shows an abnormal urinary excretion of an iduronic acid-rich low molecular weight heparan sulphate. Also, no dermatan sulphate could be detected in the urine, whereas this compound was the main sulphated glycosaminoglycan in the liver of the patient. Heparan sulphate was the main glycosaminoglycan of normal liver. The total amount of sulphated glycosaminoglycans in the urine and liver of the patient did not differ significantly from the amounts found in the liver and urine of normal subjects. Several plasma glycosidases have been assayed and the activities did not differ significantly from the values obtained for the plasma of normal subjects.

Dermatan Sulfate↗
PubMed1990

Conformationally constrained congeners of 6-aryl-5-methyl-4,5-dihydro-3(2H)-pyridazinones active on the cardiovascular system: conformational studies by molecular mechanics calculations and 1H NMR spectroscopy.

Unsubstituted phenylpyridazinones 1a and 2a and their tricyclic analogues indenopyridazinone 3a, benzocinnolinone 4a, and benzocycloheptapyridazinone 5a were submitted to conformational analysis with Allinger's MM2(85) program in order to better define the relationship between the cardiovascular properties of some derivatives and their preferred conformations. Structures 1-4, giving rise to highly active compounds, were found to exist in a conformation showing a near-planar arrangement of the phenyl and the pyridazinone ring. On the contrary, 5, whose derivatives were inactive, shows two significantly populated conformations both markedly deviated from planarity. 1H NMR analysis of the tricyclic systems 3-5 was in full agreement with the molecular mechanics calculations.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1987

A relationship between the inhibition of heparan sulfate and chondroitin sulfate synthesis and the inhibition of molting by selenate in the hemipteran Rhodnius prolixus.

The insect Rhodnius prolixus synthesizes heparan sulfate and chondroitin sulfate after a blood meal containing [35S]-inorganic sulfate. A 40 to 80% inhibition of heparan sulfate synthesis was obtained when the meal was supplemented with 10(-5) and 10(-4) M sodium selenate respectively. Likewise an inhibition of the molting in the order of 30 to 60% was observed when the insects were fed with blood containing 10(-5) and 10(-4) M selenate respectively. The insects after a subsequent meal without selenate molted normally. Except for the inhibition of the ecdysis no gross physiological or morphological changes could be observed in the insects. Based on these and other findings the possible role of sulfated glycosaminoglycans in the control of cell growth is discussed.

Animals↗
PubMed1983

Clinical and biochemical changes in a child with type I mucopolysaccharidosis during long-term transfusion of leukocytes.

The effect of two years of periodic transfusions at 2--4 month intervals of mixed leukocytes in a patient with Type I mucopolysaccharidosis is described. There was an increase of urinary chondroitin sulfate B after the first transfusion followed by a progressive decrease to 35% of the initial daily excretion. Chondroitin sulfate AC, which was almost absent prior to the transfusions, was excreted in significant amounts after the 4th transfusion. There was a decrease of hepatosplenomegaly, kyphosis and gibbus and no changes in the other signs of the disease. Regarding stature, mental development and social behavior, the patient is developing thus far as a normal child. The early diagnosis of the disease and the immediate transfusions undoubtedly have been contributing factors to the restoration and/or maintenance of the child in an almost normal condition.

Blood Transfusion↗
PubMed1979

Role of 24- and 28-hydroxylated intermediates in the metabolism of beta-sitosterol in the insect Tenebrio molitor.

1. [28-3H]Stigmast-5-ene-3 beta, 28-diol and [23,23,25-3H]stigmast-5-ene-3 beta, 24-diol were synthesized. 2. Each of the samples was mixed with beta-[4-14C]sitosterol and administered to Tenebrio molitor larvae. 3. The former compound is not utilized by the insect; the latter, although metabolized to 24(28)-ethylidene sterols and cholesterol, is not a beta-sitosterol metabolite. 4. The above results are discussed in relation to the mechanism of formation of the 24(28)-double bond in beta-sitosterol metabolism in T. molitor.

Hydroxylation↗