[The mortality due to pulmonary silicosis in the Tuscany region in the last decade demonstrates that the health effects of work exposure to silica are still marked]. / La mortalità per silicosi polmonare in Regione Toscana nell'ultimo decennio dimostra che gli effetti sulla salute dovuti all'esposizione lavorativa a silice sono tuttora marcati.

An analysis of death certificates from 1987 to 1996 among residents of the Tuscany Region identified 1518 deaths from pneumoconiosis, the large majority from silicosis, a disease explained by occupational exposure to silica dust. A dozen of deaths are from asbestosis, occurred at younger ages and are concentrated in a restricted area where a cement-asbestos factory was active. Deaths from pneumoconiosis occurred mainly among males, and the rates of the disease are decreasing only in the latest years. About 10% of deaths from silicosis are among subjects dying before 65 years of age. Mortality rates are very high in several areas of the Region, approximating those from lung cancer and ischaemic heart disease. For the above reasons the disease is still of concern from the point of view of public health and actions are suggested to obtain a description of prevalence and incidence of the disease.

Alpha-glucan synthesis on a protein primer. A reconstituted system for the formation of protein-bound alpha-glucan.

Reconstitution experiments with the DEAE-cellulose-treated enzymes, engaged in a two-step mechanism of synthesis of alpha-glucan bound to protein, are performed. Urea/sodium dodecyl sulfate/polyacrylamide gel electrophoretic analysis of the radioactive products synthesized by the reconstituted system shows highly glucosylated, labeled bands, whose apparent molecular masses change with the acrylamide concentration in the gels. The long carbohydrate chains synthesized during the second step arise from the sequential addition of glucosyl moieties to the glucoprotein formed during the first step. A deglucosylation experiment confirms that the product of the reconstituted system originates from the 38-kDa glucosylated component of the reaction 1 product by the addition of beta-amylase-sensitive glucosyl moieties. Our data suggest that specific phosphorylases and starch synthetases are found in potato tuber, which are capable of utilizing reaction 1 product as primer for the synthesis of protein-bound glucan.

alpha-Glucan synthesis on a protein primer, uridine diphosphoglucose: protein transglucosylase I. Separation from starch synthetase and phosphorylase and a study of its properties.

It was found that the DEAE-cellulose-treated UDP-Glc:protein transglucosylase I catalyzing the first step (reaction 1) in the formation of alpha-glucan bound to protein in potato tuber is not only specific for the glucosyl donor but also for the endogenous acceptor. A single radioactive 38-kDa macromolecular component appeared during denaturing polyacrylamide gel electrophoresis of reaction 1 product. The labeled component is probably the polypeptide subunit of the endogenous acceptor which is being glucosylated. The radioactivity incorporated in reaction 1 product was isolated from a protease digest as a low-molecular-mass glucopeptide fraction. A beta-elimination reaction carried out in the presence of a reducing agent demonstrated that only one glucosyl moiety is transferred from UDP-Glc to the aminoacyl residue, thus forming an O-glucosidic linkage. 3H-labeled sodium borohydride showed that serine and threonine are involved in the peptide bond to glucose. Ion-exchange chromatography on DEAE-cellulose, affinity chromatography on concanavalin-A--Sepharose, gel filtration on Sephacryl S-300 and sucrose density gradient centrifugation failed to separate the enzyme catalyzing reaction 1 from the endogenous acceptor.

A two-step enzymatic formation of a glucoprotein in potato tuber.

Evidence is presented on the occurrence of a two-step mechanism for the synthesis of protein bound glucan in a potato tuber particulate preparation. Experiments carried out with a differently labeled sugar donor for each step enabled the isolation of a double-labeled glucoprotein. Smith periodate degradation of the product confirmed this hypothesis.

A primer independent activity of rabbit muscle phosphorylase b.

Rabbit muscle phosphorylase b was found to be capable of forming protein bound alpha-1,4 glucosyl chains upon incubation of the enzyme with appropriate concentrations of glucose-1-phosphate with no primer addition (unprimed synthesis). This activity would only be present in a small fraction of the total muscle phosphorylase b activity, as judged from the high concentrations of enzyme which are required to demonstrate the occurrence of unprimed synthesis. Polyacrylamide gel electrophoresis shows the presence of a phosphorylase isoenzyme capable of accepting glucosyl moieties, giving rise to a glucosylated protein enzymatically active in the chain lengthening of its own glucan.

Biosynthesis of starch. Formation of a glucoproteic acceptor by a potato non-sedimentable preparation.

1. A non-sedimentable fraction of potato tuber has been found to catalyze [14C]glucose transfer from [14C]glucose 1-phosphate to an endogenous proteic acceptor in the absence of added primer. This transfer is activated by Mn2+. 2. The labeled glucosylated product formed is trichloroacetic acid insoluble and sensitive to proteolytic and amylolytic digestions. It appears to be a glucoprotein with glucosyl chains bound to the peptide portion of the molecule through an unknown linkage. 3. The carbohydrate portion of the glucoprotein can be released by prolonged incubations with the enzymatic preparation, and becomes in turn, trichloroacetic acid soluble and alcohol precipitable. 4. Both products, the glucoprotein as well as the alpha-1,4-glucan that seems to arise from the enzymatic cleavage of the former, can be used as primers by the transglucosylating system with ADP[14C]glucose, UDP[14C]glucose or GDP[14C]glucose as glucosyl donors. The results presented in this paper are the first demonstration of soluble glucosyl transferases with the same glucose donor specificity to that of the particulate starch synthetase. 5. This report presents further evidence in favor of the assumption of a glucoproteic intermediate in alpha-a,4-glucan synthesis initiation.

Effect of cetyltrimethylammonium bromide on the activity of particulate starch synthetase from potato tuber.

The action of some detergents on the incorporation of glucose from uridine diphosphate glucose or adenosine diphosphate glucose into the potato tuber starch grain was studied. It was found that the cationic detergent, cetyltrimethylammonium bromide, produces a rapid binding of both sugar nucleotides to the grain and a great increase in the incorporation of glucose into the polysaccharide. Kinetic constants of starch synthetase are also modified, there being an affinity increase for both sugar nucleotides. Neutral detergents are without effect and anionic detergents are inhibitors.

Some Properties of Potato Tuber UDPGd-fructose-2-glucosyltransferase (E.C. 2.4.1.14) and UDPGd-fructose-6-phosphate-2-glucosyltransferase (E.C. 2.4.1.13).

Sucrose and sucrose 6-phosphate synthetase were isolated from potato tubers, partially purified and their properties studied. The sucrose synthetase showed optimum activity at 45 degrees and was inhibited competitively by ADP and some phenolic glucosides. The Ki's for these inhibitors were determined. Mg(2+) was found to activate this enzyme. Activity toward UDP-glucose or ADP-glucose formation was measured. The optimum conditions for sucrose and UDP-glucose formation were found to differ. The specificity for the glucosyl donor and acceptor were determined.The optimum conditions for sucrose 6-phosphate synthetase activity were studied. This enzyme was not inhibited by either ADP or phenolic glucosides; UDP-glucose was the only glucosyl donor for sucrose 6-phosphate formation.

Formation of a soluble amylopectin-like polysaccharide in potato tubers.

When potato sprouts or potato tuber slices were incubated with 0.1 m glucose 1-phosphate, a soluble amylopectin-like polysaccharide was excreted to the medium. This polysaccharide was found to be a very good primer for phosphorylase and a poor one for starch synthetase. Beside the formation of this extracellular polysaccharide, a more branched intracellular polysaccharide could be isolated. This polysaccharide was an excellent primer for starch synthetase. Fructose 6-phosphate, glucose 6-phosphate, fructose 1,6-diphosphate, glucose or sucrose could not substitute for glucose 1-phosphate. 2,4-Dinitrophenol or nitrogen did not affect the excretion of the polysaccharide. Some properties of these 2 polysaccharides are described.