Scientia Sinica最新文献

In this paper, we prove by perturbational molecular orbital (PMO) theory that with polycyclic aromatic hydrocarbons (PAH) there exist two regions having electrophilic activity, which are the necessary and sufficient condition for its carcinogenic activity. We are the first to obtain a quantitative equation for the carcinogenic activity of PAH, using the carbonium ion delocalization energies as parameters. By using the equation, the calculated carcinogenic activity is in fair accord with the experiment, and the consistent ratio comes up to 98%. Further study shows that the optimum distance for carcinogenic activity approximates to 2.80 A. This is just the distance between the negative centers in DNA double helix. Therefore, the key step of the carcinogenesis for PAH in vivo is the interstrand cross linkage between the DNA complementary base pair. In terms of this deduction, we suggest that the possible mechanism of chemical carcinogenesis should be a complementary frameshift mutation between the DNA double helix. We name such an idea "di-region theory", which probably might be of general significance for other chemical carcinogenesis.

A cell-free extract containing TMV-RNA replicase was prepared from TMV-infected tobacco leaves. It could synthesize double-stranded RNAs in the presence of four nucleoside triphosphates (among them, UTP was tritium-labelled), magnesium ion and actinomycin D. It was confirmed by polyacrylamide-agarose gel electrophoresis, RNase treatment, thermal denaturation and self annealing that 3H-ds RNAs, obtained from phenol-SDS extraction and Serva cellulose column chromatography, consisted of replicative form (RF) and replicative intermediate (RI) of TMV-RNA, with molecular weights of 40 X 10(6) and 5.0 X 10(6), respectively. Molecular hybridization competition experiment showed that 60-70% of the nascent RNAs in the 3H-ds RNA were plus strand of tMV-RNA.

Three cell lines derived from liver carcinoma specimens of two male and one female operated patients have been successfully established in vitro and designated by the names of BEL-7402, BEL-7404 and BEL-7405. In the course of the establishment (from the 2nd transfer onwards) studies were made to characterize them. The doubling time of cell population was found to be 20--26 hr. They formed tumor nodules upon heterologous transplantation. They appeared as epithelial-like cells in morphology and showed, in addition to desmosomes, the presence of cytoplasmic tonofibrills which were typical of epithelial cells by electron microscopy. The ultrastructural features were different from normal human liver cells, but similar to clinical hepatoma cells. They had hypotriploid chromosone number with one abnormally long acrocentric chromosome present in all 3 cell lines and additional small acrocentric chromosome and chromosome fragment in BEL-7405 line of cells. AFP were detected intracellularly by the indirect immunofluorescent method. LDH isoenzyme showed a pattern different from that of human adult liver, but similar to those of embryonic liver and clinical hepatoma with the increase of the percentage of LDH-1 (H-type) at the expanse of LDH-5 (M-type), i.e. with a higher H/M ratio. The results suggest the 3 lines of liver carcinoma cells as rapidly growing and not well differentiated epithelial-like malignant cells.

Two hisD-unlinked genes NifC5 and NifC7 are mapped in the chromosome of K. pneumoniae. The sequence of NifC5 and NifC7 is suggested as NifC5--gltB--NifC7--argG. The P1 infected E. coli lysate can transduce the mutant C-7 to be Nif+ transductant, yet fails to transduce the hisD-linked nif mutants to be Nif+ ones. This indicates that the gene encoding C-7 is not the structural gene of nitrogen fixation and is present in E. coli. It is actually a gene specifying the glutamate synthetase. SDS electrophoresis shows the marked low content of nitrogen reductase and immunoelectrophoretic test reveals the reduced amount of both nitrogenase and nitrogen reductase in the mutant cells.

Complementation tests were performed with various nif mutations for delineating the nif genes. The nif-/nif- heterogenotes were constructed by transferring nif plasmid mutant PRD-nif- from E. coli Jc5466 to various Klebsiella pneumoniae nif- recipients. In addition to those nif genes previously reported elsewhere, a new essential gene for nitrogen fixation, nifC was identified. According to the P1-transduction and three factor reciprocal crosses, nifC was tentatively mapped between nifH and nifJ in the chromsome. The order of nif genes obtained was hisD, nifQ, nifB, nifA, nifL, nifF nifM, nifV, nifS, nifU, nifN, nifE, nifK, nifD, nifH, nifC and nifJ. The examination of the biochemical phenotypes of the nif genes suggests that nifC may be concerned with the synthesis or activation of the iron molybdenum cofactor nitrogenase, nifH, besides coding for the structure of nitrogen reductase may also exert a function on the synthesis of nitrogenase, and nifJ presumably is required to turn on the expression of nifK (D), nifH or nifF.

The effect of n-butanol on the activity of Na+, K+-ATPase has been found different at different temperatures. Below the phase-transition temperature, n-butanol has a stimulating effect provided the concentration is not higher than 0.3 M. But if the activity is determined above the phase-transition temperature, n-butanol has an inhibitory effect. The p-nitrophenyl phosphatase activity has been found to be inhibited by n-butanol even at comparatively low temperatures. This is in accord with the finding that the Arrhenius plot for p-nitrophenyl phosphatase did not show any break. It is suggested that at lower temperatures the conformational change involved in the transport of Na+, K+ ions may be the rate-limiting factor in the overall reaction, and n-butanol may be used as a probe for perturbation of the membrane to elucidate the mechanism of Na+, K+-ATPase.

This report deals with the differences and changes of physiological functions of the highlanders and the lowlanders at different altitudes during the period when the Chinese Mountaineering Team was climbing up and reached the peak of Qomolangma Feng. In a period of relaxation, there are no significant changes in ventilatory responsiveness to hypercapnia, electrocardiogram and electroencephalogram between highlanders and lowlanders with the changes at different altitudes. At 5,000 m a.s.l., however, electrocardiogram and the result of cardiac ventricular functional test show significant differences after the subjects are physically loaded. Those whose electrocardiogram readings show unusual changes, and whose cardiac ventricular functional tests show their physiological functions at low degree after physical activities at the altitude of 5,000 m, have a climbing ability hardly below 6,500 m, while those who have reached the altitudes above 8,200 m have no unusual changes in electrocardiogram, and the results of cardiac ventricular functional tests show that their physiological functions are at high degree.

The partial synthesis of harringtonine from cephaltotaxine has been described. A key intermediate, 5, 5-dimethyl-2-hydroxytetrahydrofuran-2-carboxylic acid (V), prepared from 4-methyl-1, 4-valerolactone, was dehydrated smoothly to give 5, 5-dihydrofuran-2-carboxylic acid (VI), Through its sodium salt, VI was converted into the corresponding acyl chloride VIII, which reacted with cephalotaxine in the presence of pyridine to give ester IX. After being treated with hydrichloric-acetic acid, ester IX unerwent Reformatsky reaction to give a mixture (XIV) of harringtonine and its diastereoisomer (epiharringtonine) as the final product which was purified either by countercurrent distribution or column chromatography on neutral alumina. The amounts of the two epimers in the mixture shown by TLC were roughly equal.

Changrolin is 4-(3', 5'-bis[(N-pyrrolidinyl)methyl]-4'-hydroxyanilino)-quinazoline. It is a novel type of antidysrhythmic drug. It has been synthesized in 4 steps. According to our experiments, changrolin exhibited significant protective and therapeutic effects against experimental arrhythmias induced by aconitine or ouabain. It raised the electrical threshold of ventricular fibrillation. Intravenous injections in dogs and rabbits caused (i) a mild tachycardia followed by bradycardia; (ii) a prolongation of P-R interval and a widening of QRS complex in the electrocardiogram; (iii) a gradual hypotehsion; (iv) a slight weakening of cardiac functions; and (v) only moderate influences on the hearts of dogs and rabbits when the rate of infusion was less than 1 mg/min. Changrolin could be well absorbed by oral administration. Absorption appeared to be more rapid and complete by intramuscular injection. 14C-labelled changrolin was distributed mainly in the liver and the alimentary tract.

The present paper deals with the microscopic and submicroscopic structures of the peripheral nerve of the lumbar plexus and the skeletal muscle of the m. psoas major of the ancient female cadaver buried about 2100 years ago, which was excavated from the Han Tomb No. 1 at Mawangdui (Mawangtui) near Changsha, Hunan Province. The connective tissues in the peripheral nerve and the skeletal muscle of the ancient cadaver were found well preserved. Under the electron microscope were observed the characteristic periodic bands of the collagenous fibrils as well as some axons and degenerated myelin sheath in the lumbar plexus. And in some of the better preserved nerve fibers, their axons and myelin sheaths are readily discernible. In the m. psoas major, cross striations are clearly visible in some muscle fibers. The remains of a blood vessel with only their connective tissues left were observed in the nerve of the lumbar plexus. Bacterial spores appeared in the two tissues.