中国晚期旧石器的碳-14断代和问题

根据已公布的47个碳-14数据,进而分析10处中国晚期遗址的年代和问题,并提出不同的看法。文中强调:露天遗址中碳-14数据的异常现象,往往与各种原因形成的再次堆积有关。因此必须注意样品的采集和避免引用孤零的碳-14数据,同时还要结合地层和文化性质的分析,才可能保证断代的准确性。     

Prolactin modifies the prostaglandin synthesis, prolactin binding and fluidity of mouse liver membranes

The objective of these studies was to determine if prolactin, known to induce its own receptors, alters the prostaglandin (PG) synthesis which could, in turn, modify the fluidity of the membrane and thus alter the functionality of prolactin receptors. Adult male C₃H mice were injected subcutaneously with 100 μg of oPRL every 4 h for 0, 24 or 48 h and sacrificed 8 h after receiving the last injection. Liver 100,000 × $\text{g}$ membrane pellets were used in the measurement of these parameters. The amount of binding of prolactin to these membranes increased with the duration of injections, the values being 179 and 244% of control values after 24 and 48 h of injections, respectively. The amounts of PGF_2α and PGE synthesized also increased after these injections, the values being 127 and 270% of control for PGF_2α and 634 and 695% of control values for PGE after 24 and 48 h of injections, respectively. Fluorescence polarization, an index of microviscosity, was decreased by 14 and 20% after 24 and 48 h of PRL administration, respectively. Previous studies have demonstrated simultaneous in vitro effects of prostaglandin on both prolactin receptors and membrane fluidity. The current data are in agreement with those observations and suggest that prolactin may modulate its own receptor by increasing the fluidity of the membrane in which it exists by alterations within the PG cascade. Such biochemical changes may then modify existing restraints and allow the hormone receptor to assume a more functional configuration.     

Induction and repair of DNA strand breaks in cultured human fibroblasts exposed to various phenols and dihydrodiols of benzo[a]pyrene

Cultured human fibroblasts from healthy donors were incubated for 30 min with nine different benzo[a]pyrene (BP) derivatives in the presence or absence of liver microsomes from 3-methylcholanthrene treated rats. The induction and repair of DNA strand breaks were analysed by alkaline unwinding and separation of double and single stranded DNA (SS-DNA) by hydroxylapatite chromatography immediately after the incubation or at various times after the treatment. In the absence of microsomes DNA stand breaks were detected in fibroblasts exposed to 30 microM of each of the six BP phenols (1-, 2-, 3-, 7-, 9- or 11-OH-BP) and the three BP dihydrodiols (BP-4,5-, BP-7,8- or BP-9,10-dihydrodiol). After removal of the BP derivatives from the medium the DNA strand breaks disappeared within 24 h. alpha-Naphthoflavone (alpha-NF) caused a decrease in the induction of strand breaks by 1-, 3- and 9-OH-BP but did not affect the induction of strand breaks in cells exposed to BP-7,8-dihydrodiol. In the presence of microsomes DNA strand breaks were found after exposure to 30 microM of each of the six BP phenols (1-, 2-, 3-, 7-, 9- or 11-OH-BP), as well as BP-7,8- and 9,10-dihydrodiol. In contrast BP-4,5-dihydrodiol did not induce strand breaks under these conditions. The induction of strand breaks by BP-7,8-dihydrodiol was enhanced in the presence of cytosine-1-beta-D-arabinofuranoside (AraC). In all cases the DNA strand breaks had disappeared 24 h after removal of the BP derivatives and microsomes except after treatment with BP-7,8-dihydrodiol.     

Structure-activity relationships of chlorinated benzenes as inducers of different forms of cytochrome P-450 in rat liver

Hexachlorobenzene (HCB) produced increases in ethoxyresorufin (ERR) O-deethylase, aryl hydrocarbon hydroxylase (AHH) and aminopyrine N-demethylase activities in rat liver microsomes which were intermediate between those produced by phenobarbital and 3,4-benzpyrene (BP). α-Naphthoflavone (ANF) selectively inhibited ERR activity in BP and HCB-induced microsomes (94% and 88%). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of liver microsomes indicated that HCB did not produce a detectable increase in a polypeptide with electrophoretic properties similar to those of purified cytochrome P-448 (M_r = 56 000). However, HCB did induce a polypeptide with M_r = 53 000 corresponding to one of two polypeptide bands induced by BP. This polypeptide may represent a second form of cytochrome P-448. Purification of HCB to remove possible dibenzo-p-dioxin impurities did not alter the ‘mixed-type’ induction produced by HCB. In contrast to HCB, all other chlorinated benzenes tested resembled phenobarbital as inducers.     

How long was the Younger Dryas? Preliminary evidence from annually laminated sediments of Soppensee (Switzerland)

Despite extensive AMS-¹⁴C dating series on Late-glacial terrestrial plant remains, a precise estimate of the duration of the Younger Dryas biozone (sensu Ammann & Lotter, 1989) is hampered by the occurrence of a period of constant ¹⁴C-age at 10 000 yr B.P. However, varve counts at Soppensee suggest that the Younger Dryas biozone comprises approx. 680–720 varves, and that the phase of constant radiocarbon age includes between 270–310 varves.     

多肽的α螺旋结构对多肽与钙调蛋白亲合力的影响

本文设计并采用固相法合成了4种钙调蛋白可结合多肽,这些多肽分成两组,每一组中两个多肽的碱性和疏水性相近,但形成α螺旋结构的倾向(预测)不同。研究了这些多肽与钙调蛋白的相互作用,在Ca~(2+)存在下,这些多肽与丹磺酰钙调蛋白结合,使丹磺酰钙调蛋白的荧光光谱发生显著变化,测定了多肽与钙调蛋白所形成的复合物的解离常数。结果表明,预测形成α螺旋结构倾向较大的多肽与钙调蛋白的亲合力也较大。     

Mitochondrial rps14 is a transcribed and edited pseudogene in Arabidopsis thaliana

We have isolated and analysed a 2 kb region of the mitochondrial genome of Arabidopsis thaliana (Columbia) showing a high level of nucleotide identity with the mitochondrial (mt) rps14 small-subunit ribosomal protein gene from Oenothera berteriana and Vicia faba, as well as with an open reading frame (ORF) located upstream of the nad3 locus in O. berteriana. The rps14 locus is present as a single copy in the A. thaliana mt genome and has a translational stop codon located near the initiation codon, as well as a deletion of one nucleotide that disturbs the coding sequence. The cloning and sequencing of nine amplified mt rps14 cDNAs clearly demonstrated that this gene is transcribed and that the mRNA precursors are edited at three positions, all involving C-to-U conversions. No editing events changing the stop codon and restoring the correct coding sequence were witnessed within the 9 individual cDNA clones. Therefore, we conclude that the single rps14 sequence of the mitochondrial genome from A. thealiana is in fact a pseudogene that is transcribed and edited but not translated.     

Neuroethology of olfactory preference development

Young mammals come to approach the odor of their mother, a response that facilitates their survival during early life. Young rats induce a cascade of events in their mother to induce the emission of her odor. The pups increase circulating prolactin levels, which increases food intake and the emission of large quantities of cecotrophe containing the maternal odor. This odor is synthesized by the action of cecal microorganisms and changes with maternal diet. The diet-dependence of the odor requires the pups to acquire their attraction to the odor postnatally. The acquisition of this preference occurs when an odor is paired with the tactile stimulation that pups receive during maternal care. The action of the tactile stimulation appears to be mediated by noradrenaline. The development of this type of olfactory attraction is accompanied by changes in the regions of the olfactory bulb that are responsive to the attractive odor. Metabolic, anatomical, and neurophysiological changes in response to the attractive odor emerge in such regions of the bulb after early olfactory preference training. © 1992 John Wiley & Sons, Inc.     

Photosynthetic apparatus of chilling-sensitive plants IX. The involvement of α-tocopherol in the electron transport chain and the anti-oxidizing system in chloroplasts of tomato leaves

1. The role of tocopherols in tomato chloroplasts from fresh, cold and dark-stored as well as stored and illuminated leaves was studied.2. The cold and dark storage of leaves results in a loss of chloroplast α- and γ-tocopherols of about 30–40% accompanied by an increase in chloroplast δ-tocopherol of about 40%. On illumination of stored leaves, an elevation of α- and γ-tocopherol level to about 110 and 95% of the control, respectively, occurs, whilst δ-tocopherol content is not affected.3. Experiments performed with 2,2-diphenyl-1-picrylhydrazyl-treated chloroplasts show that only about 70% of total α-tocopherol is functionally active in the electron transport of Photosystem II between the diphenyl-carbazide (DPC) donation site and the inhibition site of DBMIB.4. A small amount of α-tocopherol quinone (about 10% of α-tocopherol content) is found in chloroplasts from fresh, fresh and illuminated as well as cold and dark-stored tomato leaves, whereas the illumination of the latter increases the chloroplast α-tocopherol quinone content 3-fold. Moreover, following the illumination of chloroplasts from cold and dark-stored as well as stored and illuminated leaves, the oxidation of exogenous α-tocopherol to α-tocopherol quinone is 2-fold faster then in chloroplasts from fresh leaves.5. The primary product (‘α-tocopheroxide’) formed during the α-tocopherol oxidation by illuminated chloroplasts was identified as 8a-hydroxy-α-tocopheron.6. Exogenous α-tocopherol inhibits the lipid photoperoxidation by about 40–50% in chloroplasts from all three kinds of tomato leaf.7. The results seem to suggest that chloroplast α-tocopherol is involved in both electron transport of PS II and antioxidizing system of chloroplasts.