In methylotrophic yeasts, alcohol oxidase is the first enzyme in the methanol-utilization pathway. The genome of one such yeast, Pichia pastoris, contains two alcohol oxidase genes, AOX1 and AOX2. Sequence analysis indicated that each gene encodes a similar protein of 663 amino acids. The protein-coding regions of the genes were 92% and 97% homologous at the nucleotide and predicted amino acid sequence levels, respectively. In contrast to homology observed within the protein-coding portions of the AOX genes, no homology was found in either the 5' or 3' non-coding regions. Although alcohol oxidase is found in peroxisomes of P. pastoris, the AOX amino acid sequences did not contain a peptide sequence similar to the peroxisomal transport sequence found at the C-terminus of some peroxisomally located proteins in higher eukaryotes.

Alcohol Oxidoreductases↗

PubMedDate not supplied

Longitudinal study of the three-dimensional development of subsurface enamel lesions during in vitro demineralisation.

A longitudinal study was made of the 3D development of subsurface enamel lesions in whole human molars. X-ray microtomography (XMT) was used to measure the 3D distribution of linear attenuation coefficients in the tissue at 8-15 stages during cumulative times of 36-107 days demineralisation through approximately 1-mm-wide windows. Although lesion morphology was consistent with preferential anisotropic dissolution parallel to enamel prisms at the advancing front, detail (at a scale of approximately 100 microm) varied in relation to exposed surface sites separated by <1 mm. The distribution of mineral in the most superficial region varied across the exposed face of each lesion. Within lesions, localised foci of low mineral concentration (at a scale of approximately 200 microm) retained their general form through successive stages of demineralisation before coalescing. The most advanced regions within a lesion seemed to correspond with surface regions with lowest mineral concentration. These findings indicate that local variations in fractional pore volume of partially demineralised enamel influence the subsequent spatial development of lesions.

Dental Enamel↗

PubMedDate not supplied

Synchrotron x-ray microtomographic investigation of mineral concentrations at micrometre scale in sound and carious enamel.

Synchrotron X-ray microtomography (XMT) was used to measure the linear attenuation coefficient (LAC) for 1.9-microm sidelength voxels within approximal brown spot lesions and sound human enamel. XMT demonstrated three-dimensional features, notably sheets with approximately 30 microm periodicity having low LAC, identified as regions of demineralization corresponding to Retzius lines. Quantitative three-dimensional measurements of mineral concentration, derived from LAC with assumption of a single model composition, were consistent with previous measurements of sound and carious enamel from microradiographic projections. The uncertainty in measurements of mineral concentration and mineral fraction volume was investigated by modelling enamel with a range of composition and component densities. This analysis showed that, although mineral concentration can be determined from LAC with an error of <0.2 g cm(-3), the variation in pore fraction volume within caries lesions cannot be reliably determined from X-ray attenuation measurements alone.

Apatites↗

PubMedDate not supplied

The dentist's role in child abuse and neglect. Issues, identification, and management.

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Adolescent↗