Oral Factors Affecting Titanium Elution and Corrosion: An In Vitro Study Using Simulated Body Fluid

Objectives

Ti, which is biocompatible and resistant to corrosion, is widely used for dental implants, particularly in patients allergic to other materials. However, numerous studies have reported on Ti allergy and the in vitro corrosion of Ti. This study investigated the conditions that promote the elution of Ti ions from Ti implants.

Methods

Specimens of commercially pure Ti, pure nickel, a magnetic alloy, and a gold alloy were tested. Each specimen was immersed in a simulated body fluid (SBF) whose pH value was controlled (2.0, 3.0, 5.0, 7.4, and 9.0) using either hydrochloric or lactic acid. The parameters investigated were the following: duration of immersion, pH of the SBF, contact with a dissimilar metal, and mechanical stimulus. The amounts of Ti ions eluted were measured using a polarized Zeeman atomic absorption spectrophotometer.

Results

Eluted Ti ions were detected after 24 h (pH of 2.0 and 3.0) and after 48 h (pH of 9.0). However, even after 4 weeks, eluted Ti ions were not detected in SBF solutions with pH values of 5.0 and 7.4. Ti elution was affected by immersion time, pH, acid type, mechanical stimulus, and contact with a dissimilar metal. Elution of Ti ions in a Candida albicans culture medium was observed after 72 h.

Significance

Elution of Ti ions in the SBF was influenced by its pH and by crevice corrosion. The results of this study elucidate the conditions that lead to the elution of Ti ions in humans, which results in implant corrosion and Ti allergy.     

Structural Analysis of Free N-Glycans in α-Glucosidase Mutants of Saccharomyces cerevisiae: Lack of the Evidence for the Occurrence of Catabolic α-Glucosidase Acting on the N-Glycans

Saccharomyces cerevisiae produces two different α-glucosidases, Glucosidase 1 (Gls1) and Glucosidase 2 (Gls2), which are responsible for the removal of the glucose molecules from N-glycans (Glc₃Man₉GlcNAc₂) of glycoproteins in the endoplasmic reticulum. Whether any additional α-glucosidases playing a role in catabolizing the glucosylated N-glycans are produced by this yeast, however, remains unknown. We report herein on a search for additional α-glucosidases in S. cerevisiae. To this end, the precise structures of cytosolic free N-glycans (FNGs), mainly derived from the peptide:N-glycanase (Png1) mediated deglycosylation of N-glycoproteins were analyzed in the endoplasmic reticulum α-glucosidase-deficient mutants. 12 new glucosylated FNG structures were successfully identified through 2-dimentional HPLC analysis. On the other hand, non-glucosylated FNGs were not detected at all under any culture conditions. It can therefore be safely concluded that no catabolic α-glucosidases acting on N-glycans are produced by this yeast.     

Construction of a Pseudozyma antarctica strain without foreign DNA sequences (self-cloning strain) for high yield production of a biodegradable plastic-degrading enzyme

ABSTRACT

The basidiomycetous yeast Pseudozyma antarctica GB-4(0) esterase (PaE) is a promising candidate for accelerating degradation of used biodegradable plastics (BPs). To increase safety and reduce costs associated with the use of PaE, we constructed a self-cloning strain with high-PaE productivity. A Lys12 gene (PaLYS12)-deleted lysine auxotroph strain GB4-(0)-L1 was obtained from GB-4(0) by ultraviolet mutagenesis and nystatin enrichment. Subsequently, the PaE gene (PaCLE1) expression cassette consisting of GB-4(0)-derived PaCLE1, under the control of a xylose-inducible xylanase promoter with PaLYS12, was randomly introduced into the GB4-(0)-L1 genome. A PaE high-producing strain, PGB474, was selected from among the transformants by high throughput double-screening based on its ability to degrade emulsified polybutylene succinate-co-adipate. Quantitative PCR revealed that four copies of the PaE gene expression cassette were introduced into the PGB474 genome. PGB474 produced 2.0 g/L of PaE by xylose-fed-batch cultivation using a 3-L jar fermentor for 72 h.     

Solution properties of gellan gum: change in chain stiffness between single- and double-stranded chains

Nine samples of gellan gum in the sodium form, ranging in weight-average molar mass from 3.47 x 10(4) to 1.15 x 10(5) at 40 degrees C, were investigated by static and dynamic light scattering and viscometry in 25 mM aqueous NaCl both at 40 and at 25 degrees C. The ratios of the molar mass at 25 degrees C (in the ordered state) to that at 40 degrees C (in the disordered state) were in the range of 1.99 to 2.07, supporting the scheme of the conformational transition of gellan gum between a disassociated single chain and an associated chain composed of two molecules. Focusing on the effects of polydispersity, the intrinsic viscosities, radii of gyration, and hydrodynamic radii were analyzed on the basis of unperturbed wormlike chain models. The persistence lengths were evaluated as 9.4 nm at 40 degrees C and 98 nm at 25 degrees C.     

Identification of a SNARE protein required for vacuolar protein transport in Schizosaccharomyces pombe

Intracellular vesicle trafficking is mediated by a set of SNARE proteins in eukaryotic cells. Several SNARE proteins are required for vacuolar protein transport and vacuolar biogenesis in Saccharomyces cerevisiae. A search of the Schizosaccharomyces pombe genome database revealed a total of 17 SNARE-related genes. Although no homologs of Vam3p, Nyv1p, and Vam7p have been found in S. pombe, we identified one SNARE-like protein that is homologous to S. cerevisiae Pep12p. However, the disruptants transport vacuolar hydrolase CPY (SpCPY) to the vacuole normally, suggesting that the Pep12 homolog is not required for vacuolar protein transport in S. pombe cells. To identify the SNARE protein(s) involved in Golgi-to-vacuole protein transport, we have deleted four SNARE homolog genes in S. pombe. SpCPY was significantly missorted to the cell surface on deletion of one of the SNARE proteins, Fsv1p (SPAC6F12.03c), with no apparent S. cerevisiae ortholog. In addition, sporulation, endocytosis, and in vivo vacuolar fusion appear to be normal in fsv1Delta cells. These results showed that Fsv1p is mainly involved in vesicle-mediated protein transport between the Golgi and vacuole in S. pombe cells.     

The N-terminal region of the transmembrane domain of human erythrocyte band 3. Residues critical for membrane insertion and transport activity

We studied the role of the N-terminal region of the transmembrane domain of the human erythrocyte anion exchanger (band 3; residues 361-408) in the insertion, folding, and assembly of the first transmembrane span (TM1) to give rise to a transport-active molecule. We focused on the sequence around the 9-amino acid region deleted in Southeast Asian ovalocytosis (Ala-400 to Ala-408), which gives rise to nonfunctional band 3, and also on the portion of the protein N-terminal to the transmembrane domain (amino acids 361-396). We examined the effects of mutations in these regions on endoplasmic reticulum insertion (using cell-free translation), chloride transport, and cell-surface movement in Xenopus oocytes. We found that the hydrophobic length of TM1 was critical for membrane insertion and that formation of a transport-active structure also depended on the presence of specific amino acid sequences in TM1. Deletions of 2 or 3 amino acids including Pro-403 retained transport activity provided that a polar residue was located 2 or 3 amino acids on the C-terminal side of Asp-399. Finally, deletion of the cytoplasmic surface sequence G(381)LVRD abolished chloride transport, but not surface expression, indicating that this sequence makes an essential structural contribution to the anion transport site of band 3.     

Production of different types of mannosylerythritol lipids as biosurfactants by the newly isolated yeast strains belonging to the genus Pseudozyma

Mannosylerythritol lipids (MEL), which are abundantly secreted by yeasts, are one of the most promising biosurfactants known. To obtain various types of MEL and to attain a broad range of applications for them, screening of novel producers was undertaken. Thirteen strains of yeasts were successfully isolated as potential MEL producers; they showed high production yields of MEL of around 20 g l(-1) from 40 g l(-1) of soybean oil. Based on the taxonomical study, all the strains were classified to be the genus Pseudozyma. It is interesting to note that they were categorized into three groups according to their production patterns of MEL. The first group, which included 11 strains taxonomically closely related to high-level MEL producers such as Pseudozyma antarctica and Pseudozyma aphidis, mainly produced 4-O-[(4',6'-di-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl]-meso-erythritol (MEL-A) together with 4-O-[(6'-mono-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl]-meso-erythritol (MEL-B) and 4-O-[(4'-mono-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl]-meso-erythritol (MEL-C) as the minor components. The second group of one strain, which was related to Pseudozyma tsukubaensis, predominantly produced MEL-B. The third group of one strain, which was closely related to Pseudozyma hubeiensis, mainly produced MEL-C; this is the first observation of the efficient production of MEL-C from soybean oil. Moreover, the major fatty acids of the obtained MEL-C were C(6), C(12), and C(16) acids, and were considerably different from those of the other MEL hitherto reported. The biosynthetic manner for MEL is thus likely to significantly vary among the Pseudozyma strains; the newly isolated strains would enable us to attain a large-scale production of MEL and to obtain various types of MEL with different hydrophobic structures.     

In-situ observation of tryptophan in larval cocoon silk of the hornet Vespa simillima xanthoptera cameron by ultraviolet resonance raman spectroscopy

We performed in-situ ultraviolet resonance Raman (UVRR) spectroscopy of the larval cocoon silk of the hornet, Vespa simillima xanthoptera Cameron, and compared the result with that of the silkworm, Bombix mori. The UVRR spectrum of the hornet cocoon differed markedly from that of the B. mori cocoon: peaks attributable to tyrosine (Tyr) were observed strongly, and tryptophan (Trp) peaks weakly, in the spectrum of the B. mori cocoon, whereas peaks attributable to Trp exclusively appeared in the spectrum of the hornet cocoon.     

Formation of a lamellar compound by reaction of acrylic acid crystallosolvated in highly crystalline beta-chitin

A lamellar compound resulted from reaction of acrylic acid inside crystalline beta-chitin and the structure was investigated. Beta-chitin acts like a layered crystal, having stacked molecular sheets composed of parallel chains bound in one direction by intermolecular amide hydrogen bonding. Small guest molecules can be inserted between the molecular sheets, and a crystallosolvate can be formed. By immersion of beta-chitin in acrylic acid, a crystallosolvate was formed, which was then changed into the more stable lamellar compound by heat treatment at 105 degrees C. NMR measurement and IR spectroscopy showed that during the heat treatment there was a reaction between acrylic acid and the beta-chitin molecular sheet, but the sheet structure was maintained. By IR with deuteration, it was shown that the accessibility of solvents to this lamellar compound was greater than that for the initial beta-chitin. The lamellar compound is considered a kind of "pillared" structure related to the lamellar crystal.