Nucleation and growth of calcite on native versus pyrolyzed oyster shell folia.
(9/587)
The thin sheets of calcite, termed folia, that make up much of the shell of an oyster are covered by a layer of discrete globules that has been proposed to consist of agglomerations of protein and mineral. Foliar fragments, treated at 475 degrees C for 36 h to remove organic matter, were imaged by atomic force microscopy (AFM) as crystals grew on the foliar surfaces in artificial seawater at calcite supersaturations up to 52-fold. Crystals were also viewed later by scanning electron microscopy. After pyrolysis, the foliar globules persisted only as fragile remnants that were quickly washed away during AFM imaging, revealing an underlying morphology on the foliar laths of a tightly packed continuum of nanometer-scale protrusions. At intermediate supersaturations, crystal formation was seen immediately almost everywhere on these surfaces, each crystal having the same distinctive shape and orientation, even at the outset with crystals as small as a few nanometers. In contrast, nucleation did not occur readily on non-pyrolyzed foliar surfaces, and the crystals that did grow, although slowly at intermediate supersaturations, had irregular shapes. Possible crystallographic features of foliar laths are considered on the basis of the morphology of ectopic crystals and the atomic patterns of various surfaces. A model for foliar lath formation is presented that includes cycles of pulsed secretion of shell protein, removal of the protein from the mineralizing solution upon binding to mineral, and mineral growth at relatively high supersaturation over a time frame of about 1 h for each turn of the cycle. (+info)
Lead in calcium supplements.
(10/587)
Intercalibrated measurements of lead in calcium supplements indicate the importance of rigorous analytical techniques to accurately quantify contaminant exposures in complex matrices. Without such techniques, measurements of lead concentrations in calcium supplements may be either erroneously low, by as much as 50%, or below the detection limit needed for new public health criteria. In this study, we determined the lead content of 136 brands of supplements that were purchased in 1996. The calcium in the products was derived from natural sources (bonemeal, dolomite, or oyster shell) or was synthesized and/or refined (chelated and nonchelated calcium). The dried products were acid digested and analyzed for lead by high resolution-inductively coupled plasma-mass spectrometry. The method's limit of quantitation averaged 0.06 microg/g, with a coefficient of variation of 1.7% and a 90-100% lead recovery of a bonemeal standard reference material. Two-thirds of those calcium supplements failed to meet the 1999 California criteria for acceptable lead levels (1.5 microg/daily dose of calcium) in consumer products. The nonchelated synthesized and/or refined calcium products, specifically antacids and infant formulas, had the lowest lead concentrations, ranging from nondetectable to 2.9 microg Pb/g calcium, and had the largest proportion of brands meeting the new criteria (85% of the antacids and 100% of the infant formulas). (+info)
Marmoricola aurantiacus gen. nov., sp. nov., a coccoid member of the family Nocardioidaceae isolated from a marble statue.
(11/587)
A Gram-positive, aerobic bacterium with coccoid cells occurring singly, in pairs and in clusters was isolated from the surface of a marble statue. The peptidoglycan contain LL-diaminopimelic acid as diagnostic diamino acid and a single glycine residue as interpeptide bridge (type A3 gamma). The major menaquinone is MK-8(H4). The cellular fatty acid pattern consists of straight chain saturated and monounsaturated components and 10-methyl octadecanoic (tuberculostearic) acid as the only branched chain fatty acid. Phosphatidylinositol, phosphatidylglycerol and diphosphatidylglycerol occur as characteristic polar lipids. The DNA G + C composition is 72 mol%. According to its phylogenetic position and 16S rDNA signature nucleotides, the organism is a member of the family Nocardioidaceae. The combination of chemotaxonomic characteristics is unique within this family and supports the description of a new genus and new species, Marmoricola aurantiacus. The type strain is strain BC 361T (= DSM 12652T). (+info)
Mucins and molluscan calcification. Molecular characterization of mucoperlin, a novel mucin-like protein from the nacreous shell layer of the fan mussel Pinna nobilis (Bivalvia, pteriomorphia).
(12/587)
A cDNA expression library constructed from mantle tissue mRNA of the Mediterranean fan mussel Pinna nobilis was screened with antibodies raised against the acetic acid-soluble shell matrix of the same species. This resulted in the isolation of a 2138-base pair cDNA, containing 13 tandem repeats of 93 base pairs. The deduced protein has a molecular mass of 66.7 kDa and a isoelectric point of 4.8. This protein, which is enriched in serine and proline residues, was overexpressed, purified, and used for producing polyclonal antibodies. Immunological in situ and in vitro tests showed that the protein is localized in the nacreous aragonitic layer of P. nobilis, but not in the calcitic prisms. Because this protein of the nacre of P. nobilis exhibits some mucin-like characteristics, we propose the name mucoperlin. This is the first paper reporting the cloning of a molluscan mucin and the first molecular evidence for the involvement of a mucin in molluscan calcification. This finding corroborates our previous hypothesis that some of the proteinaceous constituents of the molluscan shell matrix would derive from mucins, common to many metazoan lineages of the late Precambrian (Marin, F., Smith, M., Isa, Y., Muyzer, G. and Westbroek, P. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 1554-1559). The adaptation of an ancestral mucin to a new function, the regulation of the mineralization process, may be one of the molecular events, among others, that would explain the simultaneous emergence of organized calcification in many metazoan lineages during the Cambrian explosion. (+info)
Hypoparathyroidism unmasked by alendronate.
(13/587)
The case of an elderly woman is reported in whom alendronate, given for osteoporosis, led to severe hypocalcaemia a few days after starting the drug treatment. This was caused by the unmasking of previously unrecognised hypoparathyroidism. (+info)
Managing heartburn at the 'base' of the GERD 'iceberg': effervescent ranitidine 150 mg b.d. provides faster and better heartburn relief than antacids.
(14/587)
BACKGROUND: Many individuals with heartburn self-medicate with antacids for relief of their symptoms. AIM: To compare efficacy of effervescent ranitidine to as-needed calcium carbonate antacids in subjects who self-treat heartburn. METHODS: A total of 155 subjects with frequent antacid-responsive heartburn were randomized to receive effervescent ranitidine 150 mg tablets b.d., or as-needed calcium carbonate 750 mg for 12 weeks. Endoscopic oesophagitis severity and mucosal histology were assessed at baseline, and at weeks 6 and 12. Heartburn frequency, severity, and antacid consumption were recorded daily, and quality of life was assessed at baseline, and at weeks 6 and 12. RESULTS: Heartburn frequency and severity were significantly decreased after 1 day of ranitidine (P < 0.02). By week 6, ranitidine had significantly decreased rescue antacid consumption (7.3 tablets, P < 0.001) vs. antacids (14.1 tablets). Endoscopic oesophagitis healing (+info)
Increased intake of calcium reverses vitamin B12 malabsorption induced by metformin.
(15/587)
OBJECTIVE: Of patients who are prescribed metformin, 10-30% have evidence of reduced vitamin B12 absorption. B12-intrinsic factor complex uptake by ileal cell surface receptors is known to be a process dependent on calcium availability Metformin affects calcium-dependent membrane action. The objective of this study was to determine the magnitude and mechanism of the reduction in serum vitamin B12 after metformin administration. RESEARCH DESIGN AND METHODS: A comparative study design was employed using 2 groups (metformin and control). A total of 21 patients with type 2 diabetes received sulfonylurea therapy; 14 of these 21 patients were switched to metformin. Monthly serum total vitamin B12 measurements and holotranscobalamin (holoTCII) (B12-TCII) were performed. After 3 months of metformin therapy, oral calcium supplementation was administered. RESULTS: Serial serum vitamin B12 determinations revealed a similar decline in vitamin B12 and holoTCII. Oral calcium supplementation reversed the metformin-induced serum holoTCII depression. CONCLUSIONS: Patients receiving metformin have diminished B12 absorption and low serum total vitamin B12 and TCII-B12 levels because of a calcium-dependent ileal membrane antagonism, an effect reversed with supplemental calcium. (+info)
Sources and mechanisms of inorganic carbon transport for coral calcification and photosynthesis.
(16/587)
The sources and mechanisms of inorganic carbon transport for scleractinian coral calcification and photosynthesis were studied using a double labelling technique with H(14)CO(3) and (45)Ca. Clones of Stylophora pistillata that had developed into microcolonies were examined. Compartmental and pharmacological analyses of the distribution of(45)Ca and H(14)CO(3) in the coelenteron, tissues and skeleton were performed in dark or light conditions or in the presence of various seawater HCO(3)(-) concentrations. For calcification, irrespective of the lighting conditions, the major source of dissolved inorganic carbon (DIC) is metabolic CO(2) (70-75% of total CaCO(3) deposition), while only 25-30% originates from the external medium (seawater carbon pool). These results are in agreement with the observation that metabolic CO(2) production in the light is at least six times greater than is required for calcification. This source is dependent on carbonic anhydrase activity because it is sensitive to ethoxyzolamide. Seawater DIC is transferred from the external medium to the coral skeleton by two different pathways: from sea water to the coelenteron, the passive paracellular pathway is largely sufficient, while a DIDS-sensitive transcellular pathway appears to mediate the flux across calicoblastic cells. Irrespective of the source, an anion exchanger performs the secretion of DIC at the site of calcification. Furthermore, a fourfold light-enhanced calcification of Stylophora pistillata microcolonies was measured. This stimulation was only effective after a lag of 10 min. These results are discussed in the context of light-enhanced calcification. Characterisation of the DIC supply for symbiotic dinoflagellate photosynthesis demonstrated the presence of a DIC pool within the tissues. The size of this pool was dependent on the lighting conditions, since it increased 39-fold after 3 h of illumination. Passive DIC equilibration through oral tissues between sea water and the coelenteric cavity is insufficient to supply this DIC pool, suggesting that there is an active transepithelial absorption of inorganic carbon sensitive to DIDS, ethoxyzolamide and iodide. These results confirm the presence of CO(2)-concentrating mechanisms in coral cells. The tissue pool is not, however, used as a source for calcification since no significant lag phase in the incorporation of external seawater DIC was measured. (+info)