Effect of N-terminal alpha-helix formation on the dimerization and intracellular targeting of alanine:glyoxylate aminotransferase.

The unparalleled peroxisome-to-mitochondrion mistargeting of alanine:glyoxylate aminotransferase (AGT) in the hereditary disease primary hyperoxaluria type 1 is caused by the combined presence of a common Pro11 --> Leu polymorphism and a disease-specific Gly170 --> Arg mutation. The Pro11 --> Leu replacement generates a functionally weak N-terminal mitochondrial targeting sequence (MTS), the efficiency of which is increased by the additional presence of the Gly170 --> Arg replacement. AGT dimerization is inhibited in the combined presence of both replacements but not when each is present separately. In this paper we have attempted to identify the structural determinants of AGT dimerization and mitochondrial mistargeting. Unlike most MTSs, the polymorphic MTS of AGT has little tendency to adopt an alpha-helical conformation in vitro. Nevertheless, it is able to target efficiently a monomeric green fluorescent (GFP) fusion protein, but not dimeric AGT, to mitochondria in transfected COS-1 cells. Increasing the propensity of this MTS to fold into an alpha-helix, by making a double Pro11 --> Leu + Pro10 --> Leu replacement, enabled it to target both GFP and AGT efficiently to mitochondria. The double Pro11 --> Leu + Pro10 --> Leu replacement retarded AGT dimerization in vitro as did the disease-causing double Pro11 --> Leu + Gly170 --> Arg replacement. These data suggest that N-terminal alpha-helix formation is more important for maintaining AGT in a conformation (i. e. monomeric) compatible with mitochondrial import than it is for the provision of mitochondrial targeting information. The parallel effects of the Pro10 --> Leu and Gly170 --> Arg replacements on the dimerization and intracellular targeting of polymorphic AGT (containing the Pro11 --> Leu replacement) raise the possibility that they might achieve their effects by the same mechanism.     

Purification, properties and assay of D-ribulose 5-phosphate 3-epimerase from human erythrocytes.

Isolated hepatocytes from female rats were cultured in HI-WO/BA medium for 6 days. To the medium was added oleate, ethanol, dexamethasone and insulin. With oleate To alone, triacylglycerol accumulated; ethanol augmented the accumulation by 90%. To the best of our knowledge, this is the first demonstration that ethanol in vitro increases the content of triacylglycerol in liver cells. Further addition of dexamethasone or insulin did not alter the accumulation of triacylglycerol, indicating that these hormones did not play permissive roles for the effect of ethanol in the present system. Dexamethasone and insulin, in the absence of ethanol, increased the accumulation of triacylglycerol by 30% and 50% respectively. The concentration of glycerol 3-phosphate was increased in the presence of ethanol; however, with time the concentration of glycerol 3-phosphate declined almost to control values, while the accumulation of triacylglycerol continued linearly; this suggests that the effect of ethanol was not mediated via fluctuations in the concentration of glycerol 3-phosphate. These results are discussed in relation to earlier investigations in vivo and in vitro.     

Nomenclature of precancerous lesions of the uterine cervix. A position paper

There is universal and almost unanimous belief that there is a need for a radical revision of the terminology relating to the epithelial abnormalities of the uterine cervix that precede invasive carcinoma. Although this belief has been held for some years, no generally accepted alternative system has, as yet, been devised. This position paper examines (1) the origin of the existing system of terminology, (2) the problems associated with this system and (3) the requirements of any new, alternative nomenclature. The various alternatives that have been suggested are considered with particular reference to their advantages and disadvantages. Only two such alternatives are considered to be acceptable, and it is suggested that neither is likely to gain universal acceptance at this time. However, it is possible that new diagnostic techniques, with their potential for a more accurate evaluation of cell abnormalities, may facilitate the development or application of an acceptable system of terminology.     

Unprecedented 34S‐enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks

In the deep biosphere, microbial sulfate reduction (MSR) is exploited for energy. Here, we show that, in fractured continental crystalline bedrock in three areas in Sweden, this process produced sulfide that reacted with iron to form pyrite extremely enriched in ³⁴S relative to ³²S. As documented by secondary ion mass spectrometry (SIMS) microanalyses, the δ³⁴S_pyrite values are up to +132‰V‐CDT and with a total range of 186‰. The lightest δ³⁴S_pyrite values (?54‰) suggest very large fractionation during MSR from an initial sulfate with δ³⁴S values (δ³⁴S_sulfate,0) of +14 to +28‰. Fractionation of this magnitude requires a slow MSR rate, a feature we attribute to nutrient and electron donor shortage as well as initial sulfate abundance. The superheavy δ³⁴S_pyrite values were produced by Rayleigh fractionation effects in a diminishing sulfate pool. Large volumes of pyrite with superheavy values (+120 ± 15‰) within single fracture intercepts in the boreholes, associated heavy average values up to +75‰ and heavy minimum δ³⁴S_pyrite values, suggest isolation of significant amounts of isotopically light sulfide in other parts of the fracture system. Large fracture‐specific δ³⁴S_pyrite variability and overall average δ³⁴S_pyrite values (+11 to +16‰) lower than the anticipated δ³⁴S_sulfate,0 support this hypothesis. The superheavy pyrite found locally in the borehole intercepts thus represents a late stage in a much larger fracture system undergoing Rayleigh fractionation. Microscale Rb–Sr dating and U/Th–He dating of cogenetic minerals reveal that most pyrite formed in the early Paleozoic era, but crystal overgrowths may be significantly younger. The δ¹³C values in cogenetic calcite suggest that the superheavy δ³⁴S_pyrite values are related to organotrophic MSR, in contrast to findings from marine sediments where superheavy pyrite has been proposed to be linked to anaerobic oxidation of methane. The findings provide new insights into MSR‐related S‐isotope systematics, particularly regarding formation of large fractions of ³⁴S‐rich pyrite.     

Substantial Metabolic Activity of Human Brown Adipose Tissue during Warm Conditions and Cold-Induced Lipolysis of Local Triglycerides

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