低剂量率下高线性能量转移碳离子束辐照人类唾液腺细胞的存活效应

利用日本千叶重离子医用加速器 HIMAC 提供的碳离子束,对人类唾液腺细胞 (HSG) 在剂量率为 0.5 Gy/h 的低剂量率条件下进行了辐照,运用标准的克隆形成法得到了 3 种不同剂量平均线性能量转移 (LET) 碳离子束辐照 HSG 细胞的剂量存活效应 . 与先前 HSG 细胞在治癌剂量率 (1~5 Gy/min) 下对相近剂量平均 LET 碳离子束辐照的剂量存活效应数据相比, HSG 细胞对高 LET 碳离子束辐射表现出明显的剂量率效应 . 为在相同条件下得到碳离子束对 HSG 细胞的相对生物学效应 (RBE) ,利用 60Co-γ射线在剂量率为 0.5 Gy/h 的条件下辐照了 HSG 细胞,得到该细胞系对低 LET 射线响应的剂量存活效应 . 与先前在治癌剂量率下得到的 RBE 值相比,低剂量率条件下得到的 RBE 值总体减小 . 由实验发现的剂量率效应及低剂量率条件下 RBE 值的减小,表明由高 LET 碳离子束造成的辐射损伤在低剂量率条件下也存在着显著的修复效应 . 据此,对辐射造成细胞致死的原因进行了探讨 .     

CHANGES OF AMINO ACID COMPOSITION OF CHLORELLA CELLS DURING THEIR LIFE CYCLE

The cells of Chlorella ellipsoidea were grown synchronously,and at different stages of their life cycle, the cells wereanalysed for their contents in amino acids existing in freeforms as well as in the fractions of bulk protein and peptides.Throughout the algal life cycle, the content of bulk protein(per unit dry weight of cells) remained relatively constant,being about 20 to 40 times those of peptides and free aminoacids. The amino acid composition of the protein fraction alsoremained fairly constant, the predominant amino acids beingalanine, glutamic acid, glycine and leucine. The contents inthe bulk peptides increased appreciably during the periods ofgrowth and "ripening" (light period), and decreased markedlyduring the periods of "post-ripening" and cellular division(dark period). Similar modes of change in content were alsoobserved in most of the individual amino acids contained inthe peptide fraction. The most abundant component in the peptidefraction was arginine followed by glutamic acid, glycine andcyst(e)ine. Rather irregular was the mode of change of the levelsof individual free amino acids, although, as a whole, theirbehavior was similar to that of bulk peptides, increasing duringthe light period and decreasing during the dark period. Themost predominant free amino acids were glutamic acid and alaninefollowed by proline. Experimental evidence showed that the processes of formationof free amino acids and peptides are for the most part lightdependent, while the synthesis of protein, which is thoughtto be effected using as building blocks mostly free amino acids—formeddirectly or indirectly from early photosynthates or derivedfrom pre-formed peptides—is essentially a light-independentprocess. Peptides, as a whole, seem to have significance asreservoirs of building blocks for the syntheses in the darkof protein and other nitrogenous cellular substances. The synthesisof protein in the dark takes place not only by consuming thefree amino acids and peptides that have been accumulated duringthe light period, but also by assimilating the exogenous nitrogensource (nitrate). The distribution of individual amino acidsin the three main fractions mentioned above as it changed duringthe course of algal cell cycle was followed in detail, and theresults obtained were discussed in relation to various relevantdata reported by other workers. (Received June 29, 1964; )     

Synchronization of Mating Reactivity Rhythms in Populations of Paramecium bursaria

Cell populations of Paramecium bursaria show arhythmic mating reactivity after exposure to constant light (LL) for more than 2 wk. After this arhythmic population is exposed to darkness for 9 h, the mating reactivity rhythm of the cell population reappears. The phases of rhythms in individual cells are synchronized to each other. When the arhythmic population in constant light is exposed to dark pulses of various durations, the first peak of the recovered mating reactivity rhythm appears 6 h after the end of the dark pulse. Thus, in the case of dark pulses to cells in LL, the transition from dark to light sets the phase of the subsequent mating reactivity rhythm. When an arhythmic population in LL is transferred to constant darkness (DD), a rhythm of mating reactivity also appears and, in this case, the first peak of the rhythm occurs 18 h after the LL to DD transition. Therefore, arhythmic populations of cells in LL can be synchronized by either a dark pulse or by transition to continuous darkness. When the arhythmic populations in LL were transferred to various light/dark (LD) cycles, the mating reactivity rhythms entrained to LD cycles of 18 to 30 h in duration. Finally, mating rhythms can also be synchronized by treatment with puromycin (400 μg/ml for 6–18 h).     

Changes in composition patterns of basic proteins in Chlorella cells during their life cycle

1. (1) Changes in the composition pattern of acid soluble basicproteins in Chlorella cells during their life cycle were studiedusing various methods of fractionation ; i. e., extraction,chromatography on CM-Sephadex column and electrophoresis onpolyacrylamide gel, etc.
2. (2) The content of basic proteinswas of the order of 1-2.5%of the dry weight of cells and showeda maximum at the D_n stageand a minimum at the formative stages(L₂, L₃). The change wasdue to basic proteins (I-HC1) whichwere insoluble in 0.14 MNaCl and were non-elutable with 2 MNaCl from CM-Sephadex. The0.14 M NaCl soluble basic proteincontent remained almost constantthroughout the life cycle.
3. (3) The I-HC1 fraction in question showed 20 bands and shouldersin electrophoresis on polyacrylamide gels. Some components showedremarkable changes in their relative quantities during the lifecycle, while others exhibited relatively little change.
4. (4)Preliminary fractionation experiments of subcellular componentsby a non-aqueous method showed that the basic proteins showingmarked changes in their relative amounts were present in a nucleus-richfraction, and those exhibiting little change were found in achloroplast-rich fraction, except one main component which showedcharacteristic behavior.

(Received June 22, 1968; )     

Regulation of photosynthetic carbon metabolism in synchronously growing Chlorella pyrenoidosa

The physical properties and photosynthetic metabolism of synchronizedcells of Chlorella pyrenoidosa are described. Cells, synchronizedby successive periods of light and dark, photosynthesized understeady-state conditions for 30 min with ¹⁴CO₂. Pool sizes ofmetabolic intermediate compounds, and rates of flow of carbonthrough these pools, were determined. Cell properties and metabolismwere studied for cells just divided, at three periods duringthe growing stage, at the time of maximum DNA synthesis, justprior to division (after continuous light, and after 5 hr darkness),and following division after continuous light for 37 hr. Changes in pool sizes and flow rates are correlated with relativeshifts between amino acid and protein synthesis, which is greatestduring the growing period and DNA-synthesizing stage, and sucrosesynthesis, which is greatest in the divided cells (after darkness)and pre-division cells (after darkness). The effects of thestage of cell growth and of a prior period of darkness can beseparated to some extent by these studies, and in some respectsare additive. Specific sites of metabolic regulation discerned in these experimentsinclude the following: 1) Ribulose diphosphate carboxylase,2) fructose diphosphatase and sedoheptulose diphosphatase, 3)the synthesis of sucrose, probably at the reaction between fructose-6-phosphateand uridine diphosphoglucose to give sucrose phosphate and uridinediphosphate, 4) amino acid synthesis, at the level of nitratereduction, and 5) amino acid synthesis, at the level of carbonflow from the photosynthetic carbon reduction cycle to aminoacid carbon skeletons. (Received October 31, 1969; )     

Difference in nitrate reduction in "light" and "dark" stages of synchronously grown Chlorella pyrenoidosa and resultant metabolic changes

Using synchronized cells of Chlorella pyrenoidosa, the incorporationpatterns of ¹⁴C into various metabolites with and without nitrogensources were studied under steady-state and non steady-stateconditions. From the patterns it was found that the smallestcells which are divided in the dark utilize nitrate and nitritevery little, if at all. The importance of ammonia for regulation of secondary flow forChlorella is discussed and the suggested regulatory points aredescribed. ¹This work was sponsored, in part, by the U.S. Atomic EnergyCommission (Received January 26, 1970; )     

CHANGE OF B-TYPE HAEM CONTENT IN RELATION TO PEROXIDASE BIOSYNTHESIS IN INJURED SWEET POTATO ROOTS

The methods of quantitative analysis of b-type haem in plantswere investigated. With an improved method developed was determinedthe haem content in the supernatant, mitochondrial, and microsomalfractions of sweet potato tissue. The activities of peroxidase,catalase, and cytochrome oxidase, as well as the contents ofb-type haem and acid-insoluble nitrogen in the cellular fractionswere determined at different incubation times after cuttingof sweet potato tissue. Peroxidase and catalase increased withtime in each celluler fraction, following a short lag phase.In the mitochondrial fraction, b-type haem, cytochrome oxidase,and acid insoluble nitrogen increased linearly with time. Inthe microsomal and supernatant fraction, b-type haem increasedwith time following a short lag phase. The increase in haemcontent of the supernatant fraction appeared to be associatedwith peroxidase formation. Time course analysis showed that ⁵⁹Fe-incorporation into b-typehaem of the supernatant fraction increased with time and thatincorporation was markedly inhibited by blasticidin S. The incorporationof ⁵⁹Fe into mitochondrial haem did not increase with time andwas not inhibited by blasticidin S. Blasticidin S inhibited⁵⁹Fe-incorporation into microsomal haem. Time course analysisof b-type haem content, ⁵⁹Fe-incorporation into b-type haem,and peroxidase activity suggest that in the injured tissue haemis synthesized from low molecular weight compounds and is incorporatedinto peroxidase as the haem moiety. ¹ This paper constitutes Part 57 of the Phytopathological Chemistryof Sweet Potato with Black Rot. ² Present address: Institute for Plant Virus Research, Chiba.