The effects of guanine and cytosine variation on dinucleotide frequency and amino acid composition in the human genome

Summary One hundred twelve human DNA sequences were analyzed with respect to dinucleotide frequency and amino acid composition. The variation in guanine and cytosine (G+C) content revealed: (1) at 2–3 and 3-1 doublet positions CG discrimination is attenuated at high G+C, but TA disfavor is enhanced, and (2) several amino acids are subject to G+C change. These findings have been reported in part for collections of sequences from various species. The present study confirms that in a single organism-the human-the G+C effects do exist. Aspects of the argument that connects G+C with protein thermal stability are also discussed.     

Insulin uptake by rat liver endothelium studied in fractionated liver cell suspensions

Summary Cellular distribution of insulin receptors was studied in fractionated rat liver cell suspensions using ¹²⁵1-insulin and a visual probe consisting of latex beads covalently linked to insulin (minibeads). Fractionation was done on metrizamide gradients which yielded two cellular fractions. The large cell fraction consisted mostly of hepatocytes and the small cell fraction consisted of 37% endothelial cells as well as Kupffer cells. The magnitude of insulin uptake by the endothelium-rich small cell fraction was at least double that of the uptake by the hepatocyte-rich fraction. The minibead technique demonstrated that in the small cell fraction only endothelial cells, and not Kupffer cells, were responsible for the insulin uptake. Our findings suggest that liver endothelium may be responsible for the uptake of circulating insulin and its transport to hepatocyte. This emphasizes the presence of a tissue-blood barrier in the liver.Abbreviations PRS phosphate-buffered saline - SEM scanning electron microscopy - TEM transmission electron microscopy     

A possible discrepancy between the exposed and the whole population depending on range-size and trap-spacing in vole populations

Population Ecology - From a field study for the vole population (Clethrionomys rufocanus) in Hokkaido in the late summer of 1965, it has been proved that the range length may decrease from 25 to 18...     

Promotion of Cocklebur Seed Germination by Allyl, Sulfur and Cyanogenic Compounds

The effects of allyl, sulfur and cyanogenic compounds on thegermination of upper cocklebur (Xanthium pennsylvanicum Wallr.)seeds were examined. Mercaptoethanol and methylmercaptan aswell as KCN, substrates for rßcyanoalanine synthase(CAS), and H₂S and thiocyanate, the products of the CAS catalyzingreaction, were effective in promoting germination, suggestingthe involvement of CAS in germination. Most of allyl compounds, especially allylthiourea, as well asethylene which activated CAS [Hasegawa et al. (1994) Physiol.Plant. 91: 141], promoted the germination in an abnormal typewhich occurred by the predominant growth of cotyledons as didC₂H₄ [Katoh and Esashi (1975) Plant Cell Physiol. 16: 687].However, they failed to activate CAS unlike ethylene, and toliberate free ethylene during an incubation period. It was thuspossible that an C₂H₄-like double bond within allyl compoundscan act to promote seed germination. (Received June 10, 1996; Accepted August 21, 1996)     

Role of ω-3 fatty acid desaturases in the regulation of the level of trienoic fatty acids during leaf cell maturation

Trienoic fatty acids, namely -linolenic acid and hexadecatrienoic acid, present in leaf lipids are produced by -3 fatty acid desaturases located in the endoplasmic reticulum and plastid membranes. The changes in the level of trienoic fatty acids during leaf maturation were investigated in wild-type plants of Arabidopsis thaliana (L.) Heynh. and in the fad7 mutant deficient in the activity of a plastid -3 desaturase. The levels of trienoic fatty acids increased in 26 °C- and 15 °C-grown wild-type plants with maturation of leaves. The increase in trienoic fatty acids was mainly due to galactolipids enriched in plastid membranes. In addition, the relative levels of trienoic fatty acids in major glycerolipids, including phospholipids enriched in the endoplasmic reticulum membranes, also increased with leaf maturation. By contrast, when the fad7 mutant was grown at 26 °C, the relative levels of trienoic fatty acids in individual lipids decreased with leaf maturation. The decreases in the levels of trienoic fatty acids, however, were alleviated when the fad7 mutant was grown at 15 °C. These results suggest that the plastid -3 desaturase plays a major role in increasing the levels of trienoic fatty acids with leaf maturation.Abbreviations 163 hexadecatrienoic acid - 183 -linolenic acid - DGD digalactosyldiacylglycerol - MGD monogalactosyldiacylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - TA trienoic fatty acid - WT wild type - -3 refers to the position of the double bond from the methyl end of a fatty acid This research was supported in part by Grants-in-Aid for Scientific research (#07251214 and #06804050 to K.I.) from the Ministry of Education, Science and Culture, Japan, and by the research grant from Shorai Foundation.