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Biomedical subjects

L H Rome

Publications and source records attributed to L H Rome.

71 records · Page 4Linked to original sources
PubMed1983

Coated vesicles from rat liver and calf brain contain lysosomal enzymes bound to mannose 6-phosphate receptors.

Coated vesicles from calf brain and rat liver contain cryptic receptors which recognize and bind lysosomal enzymes via mannose 6-phosphate residues on oligosaccharide side chains (Campbell, C. H., Fine, R. E., Squicciarini, J., and Rome, L. H. (1983) J. Biol. Chem. 258, 2628-2633). In addition to mannose 6-phosphate receptors, we now report that coated vesicles from calf brain and rat liver contain the lysosomal enzymes alpha-L-fucosidase, beta-galactosidase, beta-glucosidase, beta-hexosaminidase, alpha-L-iduronidase, and alpha-mannosidase. Enzyme activities co-migrated with coated vesicles purified by agarose gel electrophoresis. Treatment of intact coated vesicles with pronase (0.05 mg/ml) had little effect on lysosomal enzyme activities, whereas a similar treatment of coated vesicles in the presence of 0.045% taurodeoxycholate resulted in the loss of most of the enzyme activities. Addition of 10 mM mannose 6-phosphate to disrupted liver coated vesicles specifically displaced up to 80% of the cryptic lysosomal enzyme activity. Disrupted liver coated vesicles and highly purified liver lysosomes were treated with anti-beta-hexosaminidase A and anti-beta-galactosidase antibodies and immunoprecipitates were analyzed by polyacrylamide gel electrophoresis. High molecular weight bands were present in the coated vesicle immunoprecipitates which were not present in the lysosome immunoprecipitates. The data suggest that coated vesicles contain mannose 6-phosphate receptor-bound lysosomal enzymes, some of which are of a higher molecular weight form. These higher molecular weight forms may represent newly synthesized enzymes that are en route to lysosomes.

Animals↗
PubMed1983

Incorporation of mannose 6-phosphate receptors into liposomes. Receptor topography and binding of alpha-mannosidase.

A receptor that binds the lysosomal enzyme alpha-mannosidase via mannose 6-phosphate moieties (mannose 6-phosphate receptor) was purified from Swarm-rat chondrosarcoma and bovine liver microsomal membranes. Receptor-reconstituted liposomes were prepared by dialysis of taurodeoxycholate-dispersed lipids with purified mannose 6-phosphate receptor. Liposomes appeared by electron microscopy as 60-120 nm unilamellar vesicles. Receptor-reconstituted liposomes retained the ability to bind alpha-mannosidase specifically. Binding was saturable with an apparent Kd of 1 nM and was competitively inhibited by mannose 6-phosphate (Ki 2mM). Liposomes containing entrapped 125I-bovine serum albumin were used to demonstrate that treatment with 0.045% taurodeoxycholate rendered liposomes permeable to macromolecules without solubilizing the membrane. Receptor orientation in the liposome membrane was established by measuring binding of ligand to intact and detergent-treated liposomes. Unlike coated vesicles, which contain cryptic mannose 6-phosphate receptors [Campbell, Fine, Squicciarini & Rome (1983) J. Biol. Chem. 258, 2526-2533], treatment of liposomes with detergent revealed no additional cryptic binding sites. In addition, treatment of liposomes with 0.75% trypsin abolished total receptor binding activity. The results suggest that the receptor is inserted with its binding site facing the outside of the liposome.

Animals↗
PubMed1983

Utilization of exogenously added acetyl coenzyme A by intact isolated lysosomes.

Acetyl coenzyme A has been shown to be required for heparan sulfate degradation for the acetylation of terminal alpha-linked glucosamine residues (Klein, U., Kresse, H., and von Figura, K. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 5185-5189). We can now demonstrate this requirement in intact isolated lysosomes. When lysosomes deficient in the enzyme alpha-N-acetylglucosaminidase were incubated at 37 degrees C with [3H]acetyl-CoA, tritium was incorporated primarily into glycosaminoglycans. By utilizing hydrolytic enzymes of known specificity, the labeled glycosaminoglycan was identified as heparan sulfate and the radioactivity was shown to be located in acetyl moieties of terminal alpha-N-acetylglucosamine residues. The acetylation of heparan sulfate in alpha-N-acetylglucosaminidase-deficient lysosomes could be stimulated by the addition of 0.5 mM ATP. Lysosomes from normal cells produced some labeled heparan sulfate; however, these organelles showed a significant incorporation of [3H]acetate into free N-acetylglucosamine that was increased over 10-fold by the addition of ATP. The N-acetylation was catalyzed by the enzyme acetyl-CoA:alpha-glucosaminide N-acetyltransferase since lysosomes deficient in this enzyme were unable to incorporate [3H]acetate into either heparan sulfate or N-acetylglucosamine even in the presence of ATP. Incorporation of [3H]acetate from [3H]acetyl-CoA into heparan sulfate (by alpha-N-acetylglucosaminidase-deficient lysosomes) and into N-acetylglucosamine (by normal lysosomes) showed a similar concentration dependence. The concentration for half-maximal incorporation of [3H]acetate was approximately 1 microM for both.

Acetyl Coenzyme A↗
PubMed1983

Coated vesicles from rat liver and calf brain contain cryptic mannose 6-phosphate receptors.

Highly purified clathrin-coated vesicles, isolated from rat liver and calf brain, contain mannose 6-phosphate receptors. The coated vesicle receptors appear to have the same subunit molecular weight and similar binding affinity as the receptor previously purified from bovine liver and rat chondrosarcoma microsomes (Sahagian, G. G., Distler, J. J., and Jourdian, G. W. (1981) Proc. Natl. Acad. Sci. U. S. A. 78, 4289-4293 and Steiner, A. W., and Rome, L. H. (1982) Arch. Biochem. Biophys. 214, 681-687). There is a considerable (greater than 60-fold) enrichment of receptors in liver coated vesicles as compared to liver microsomes. Experiments carried out with intact and detergent-disrupted coated vesicles indicated that the receptors face toward the inside of the coated vesicles. The data suggest that coated vesicles are involved in the intracellular transport of the mannose 6-phosphate receptor.

Animals↗
PubMed1981

Degradation of mucopolysaccharide in intact isolated lysosomes.

The function of isolated lysosomes was studied by measuring mucopolysaccharide degradation. Cultured human diploid skin fibroblasts were grown in medium containing H235SO4 to label endogenous mucopolysaccharide. Lysosome containing preparations at various stages of purity were isolated from disrupted cells. These preparations degraded mucopolysaccharide as indicated by the release of radioactive sulfate. Degradation was temperature-dependent, required intact lysosomes, and was optimal when incubation was carried out at neutral pH in a buffer of low ionic strength. Lysosomes from Hurler fibroblasts were unable to carry out the degradative process. ATP at 0.5 mM was found to stimulate both the rate and the extent of mucopolysaccharide degradation; GTP, UTP, and CTP had similar effects, whereas the noncleavable ATP analog adenosine 5'-(beta gamma-imido)triphosphate gave no stimulation. The ATP stimulation was inhibited by nigericin. ATP also stimulated chloroquine accumulation in lysosomes, the magnitude of which was used to measure the change in intralysosomal pH. The presence of ATP was associated with acidification of lysosome pH by 0.23 units. Acetyl coenzyme A was also found to stimulate lysosome function. This reagent, however, had no effect on chloroquine accumulation and thus appears to stimulate mucopolysaccharide degradation by a mechanism different than that caused by ATP.

Acetyl Coenzyme A↗
PubMed1979

Two species of lysosomal organelles in cultured human fibroblasts.

Cultured diploid human skin fibroblasts were fractionated by a procedure that maximizes recovery of particles containing acid hydrolases. The cells were detached by controlled trypsinization, disrupted by N2 cavitation at low pressure and fractionated at 18,000 x g on a self-generating gradient of colloidal silica. This procedure separated two species of particles that could be consisered lysosomal. The denser one (peak density 1.11) was apparently free of other contaminants, but the more buoyant one (peak density 1.085) sedimented with or close to the peaks of other organelles, including mitochondria, Golgi, endoplasmic reticulum and plasma membranes. The two populations of particles contained acid hydrolases (phosphatase, six glycosidases and four cathepsins) in roughly equal proportions, displayed latency, had similar turnover of 35S-mucopolysaccharide in normal as well as in iduronidase-deficient cells, and were recipients of alpha-L-iduronidase, previously shown to be acquired by receptor-mediated endocytosis. Acid phosphatase staining of the intact fibroblasts showed residual bodies scattered throughout the cytoplasm and, near the nucleus, a prominent network of tubules and associated dilatations and knob-like enlargements. In both thin and thick sections, these appeared continuous, as if forming a three-dimensional network similar to the network described by Novikoff (1976) as GERL. Ultrastructural studies of the isolated fractions showed the denser lysosomal peak to be composed of small round or oblong acid phosphatase-positive bodies. The more buoyant peak contained the nonlysosomal organelles predicted from the biochemical markers, small acid phosphatase-positive bodies and large multivesiculated structures in which acid phosphatase was localized in a matrix surrounding apparently empty vesicles. These large structures may represent fragments of GERL. We suggest that the dense and buoyant lysosomal organelles originate primarily from residual bodies and the GERL network, respectively.

Cathepsins↗
PubMed1979

Direct demonstration of binding of a lysosomal enzyme, alpha-L-iduronidase, to receptors on cultured fibroblasts.

Receptor-binding of "high-uptake" forms of lysosomal enzymes to human diploid skin fibroblasts had been predicted from the Michaelis--Menten kinetics of uptake of these enzymes [e.g., Sando, G.N. & Neufeld, E.F. (1977) Cell 12, 619--627]. We have now demonstrated such binding directly by using a sensitive assay for the bound enzyme. Cells deficient in alpha-L-iduronidase were detached from plastic dishes by mild trypsinization, allowed to recover, and used in suspension. They were incubated with urinary alpha-L-iduronidase at 0 degrees C for 90 minutes and then washed by centrifugation through concentrated bovine serum albumin; the activity of the cell-associated enzyme was measured with 4-methylumbelliferyl alpha-L-iduronide as substrate. A Scatchard analysis showed 14,000 binding sites per cell and a Kd of 1 x 10(-9) M for high-uptake alpha-L-iduronidase; binding of the low-uptake form was barely detectable. Mannose 6-phosphate, a known competitive inhibitor of uptake, inhibited the binding competitively, with Ki = 1 x 10(-4) M. Unexpectedly, mannose 6-phosphate greatly accelerated the dissociation of bound enzyme. During uptake of alpha-L-iduronidase at 35 degrees C, the receptors were regenerated every few minutes, even in the absence of protein synthesis.

Calcium↗
PubMed1976

Aspirin as a quantitative acetylating reagent for the fatty acid oxygenase that forms prostaglandins.

A selective acetylation of the prostaglandin-forming fatty acid oxygenase (part of the prostaglandin "synthetase" system) occurs with 100 muM concentrations of aspirin (acetylsalicylic acid). The amount of acetylation, measured by counting the [3H]acetyl-protein formed, was proportional to the amount of active, functional oxygenase in a sample. When samples were aged to allow spontaneous inactivation of the oxygenase, the amount of acetylation was proportional to the remaining measurable activity rather than the initial amount of oxygenase protein in the sample. Diethyl dithiocarbamate inhibited the oxygenase activity, but did not interfere with the subsequent acetylation by aspirin. Indomethacin, on the other hand, appeared to inactivate the oxygenase in a manner that interfered only partially with the action of aspirin as an acetylating reagent. The amount of acetylation appeared to be dependent upon the amount of native, undenatured enzyme. The results suggest that the acetylation may be dependent upon an essential functional group or conformation of groups in the catalytic peptide chain(s) that can be destroyed during spontaneous inactivation of the oxygenase, and altered by indomethacin.

Acetylation↗
PubMed1975

Properties of a partially-purified preparation of the prostaglandin-forming oxygenase from sheep vesicular gland.

The fatty acid oxygenase of sheep vesicular glands was solubilized with Tween-40 and purified 60-fold using ammonium sulfate precipitation and Deae-cellulose chromatography. Glycerol (50%) stabilized the activity at all stages of purification and allowed long-term storage at -60 degrees. The partially purified enzyme contained less than 0.7 nmoles of iron per mg of protein and less than 0.1 nmole of copper per mg of protein. Although the KI values for aspirin, BL-2338, flurbiprofen and ibuprofen remained relatively unchanged during purification, the apparent KI value for inhibition by indomethacin decreased from 120 to 2.7 muM.

Ammonium Sulfate↗
PubMed1975

Structural requirements for time-dependent inhibition of prostaglandin biosynthesis by anti-inflammatory drugs.

Several anti-inflammatory drugs have been examined for their ability to cause a time-dependent destruction of the fatty acid oxygenase that produces prostaglandins. All of the time-dependent inhibitors contained carboxylic acid moieties, and in addition all but one of the drugs contained a halogen atom. Structural analogs (of the time-dependent inhibitors) lacking halogen atoms were unable to cause a time-dependent destruction of the enzyme. The time-dependent property of an inhibitor was totally eliminated after methylation of the carboxylate group. Methylation did not, however, alter the ability of the inhibitors to competitively inhibit the oxygenase. Thus, the reversible binding of the agents at the active site was not appreciably dependent upon the free carboxyl group, whereas the subsequent irreversible process was.

Anti-Inflammatory Agents↗