The significance of the aprotic solvent in monomer studies related to the primary subunit environment in the macromolecule

An advantage of aprotic polar solvent systems in the study of monomer interactions relevant to the macromolecular state is demonstrated with the measurement of nucleoside amino proton exchange rates in DMSO/water mixtures. The DMSO/water solvent provides the first unequivocal observation of general acid catalysis of nucleic acid amino proton exchange, which is undetectable in aqueous solution due to the formation of the endocyclic protonated nucleobase. Suppression of nucleobase protonation in the presence of buffer acid is a consequence of anion desolvation in the aprotic solvent. The detected route of general acid catalysis is demonstrated as a consequence of Watson-Crick H-bonding, leading to the implication that amino chemistry is modulated in the helical state to decrease amino proton lifetime in the closed macromolecular context of conformational information obtained by hydrogen exchange methods. This useful property of the aprotic solvent can be extended to monomeric studies pertaining to specific local site interactions affecting the function and conformation of proteins and nucleic acids.     

Paper replication method for isolation of radiation-sensitive mutants.

A filter paper replication system particularly useful for isolation of radiation-sensitive mutants of pigmented bacteria was devised. The fidelity of replication was high. Adhesion between a paper disk and a properly dried master plate provided adequate contact pressure. The replicas arising from this technique constitute a convenient apparatus for general application in isolation of clones sensitive to a discriminating treatment.     

Postural influence on maternal capillary oxygen and carbon dioxide tension

The effect of posture on maternal capillary blood Po₂ and Pco₂ was studied in pregnant and non-pregnant women. There was a significant decrease of Po₂ (mean 13·0 mm. Hg) and significant decrease of Pco₂ (mean 2·4 mm. Hg) when pregnant women sat up, but these changes did not occur in the non-pregnant. These findings may be relevant to debate on the optimum posture for labour.     

L-乳酸脱氢酶热变性的热力学研究

用差示扫描量热法对L-乳酸脱氢酶的热变性进行了研究(温度扫描范围为290—390K,酶蛋白溶液浓度为0.28—0.72mg蛋白/mg溶液)。实验观察到当酶溶液浓度在0.62—0.72mg蛋白/mg溶液范围内有一个吸热转变,酶溶液浓度小于0.62mg蛋白/mg溶液时有两个未完全分开的吸热转变。 这个酶的量热焓与范德霍夫焓的比远大于1,而接近于2,这表明乳酸脱氢酶的变性过程不是一个简单的两态转变,从热力学和吸热峰的形状、大小分析,可以推断乳酸脱氢酶分子是由两个以弱相互作用相连结的合作结构区组成,而每一个结构区是由两个相互作用很强的亚基组成。也就是说乳酸脱氨酶的变性过程包括两个半独立的合作结构区的转变,每一个结构区的转变都近似一个两态转变,ΔHeal与ΔHvh的比值是随着两个半独立部分相互作用的增强,即蛋白浓度的增加而减小。随着蛋白浓度的减小,蛋白质周围水分子增多,酶分子中两个半独立部分的相对独立性增强,这可由热谱图上一个吸热转变变成两个半独立的转变得到证实。     

化学诱导的B95-8细胞中TK酶的分离和性质研究

巴豆油和正丁酸钠(nSB)诱导Raji和B95-8细胞株生成胸腺嘧啶核苷激酶(TK),其粗提液,经DEAE—纤维素柱层析,可分成两个性质不同的TK活性峰—峰Ⅰ和峰Ⅱ:(1)峰Ⅰ是穿过峰,峰Ⅱ为洗脱峰,在120mMol/L从K_2HPO_4缓冲液时洗脱下来;(2)峰Ⅱ含量在病毒生产性细胞B95-8中高于非生产性的Raji细胞;(3)B95-8细胞经联合诱导48小时后,峰Ⅱ比活性最高;(4)TTP对峰Ⅰ和峰Ⅱ的抑制效应不同,两峰利用GTP能力也不同;(5)PAGE结果表明:峰Ⅰ的Rm值为0.044,峰Ⅱ呈现两条带,Rm值分别为0.015和0.276;(6)峰Ⅰ的Km值为0.86μMol/L,峰ⅡKm值为0.29μMol/L。根据以上的结果,我们认为:峰Ⅰ是细胞TK(C-TK),而峰Ⅱ具有许多疱疹病毒TK的特性,因此,峰Ⅱ是EB病毒相关TK(EBV-TK)。     

Linkage analysis of families with hereditary retinoblastoma: nonpenetrance of mutation, revealed by combined use of markers within and flanking the RB1 gene.

Nonpenetrance of the inherited mutation responsible for retinoblastoma has been reported. By DNA analysis in families with hereditary retinoblastoma, it is possible to identify healthy individuals in whom the mutation is nonpenetrant. This requires the use of DNA markers both within and flanking the retinoblastoma gene. We have analyzed the segregation of several markers in 19 families (69 meioses) with hereditary retinoblastoma. In two families a carrier was identified who showed nonpenetrance of the mutation predisposing to retinoblastoma. The intragenic markers were informative in 15 pedigrees. The use of flanking markers from the same chromosomal region caused an increase of the number of informative families to 18. No crossing-over within the gene was observed. In one family an inherited deletion involving one of the RB1 alleles was detected. Our findings emphasize the use of a combination of both intragenic and flanking markers to obtain both the highest reliability of carrier detection in families with hereditary retinoblastoma and an accurate estimate of the frequency of nonpenetrance.     

Additive inheritance of resistance to pod rot caused by Phytophthora palmivora in cocoa

Summary Quantitative inheritance of resistance to Phytophthora pod rot (Ppr) was studied in cocoa hybrid progeny from 12 Trinitario x Amazonian crosses and their reciprocal crosses. The crossing scheme was similar to a factorial design. Disease was assessed by the number and percentage of infected pods on each tree. Highly significant differences due to general combining abilities (GCA) were obtained for all characters, except for the GCA of Trinitario on total pod production. Differences for specific combining ability (SCA) were not significant for all characters. There were no significant differences between reciprocal crosses. The Trinitario clone K82 provided the only source for the hybrid progenies of strong Ppr resistance to the hybrid progenies, while K20 provided moderate resistance. Other parental clones — KA2-101, KA5-201, KEE 2, KEE 5, and KEE 52 — produced progenies which were susceptible to Ppr. It is evident that resistance to Ppr in cocoa is inherited additively. Maternal and cytoplasmic effects were assumed to have no influence on inheritance of resistance. It is also concluded that resistance to Ppr of the kind shown by K82 is likely to be horizontal resistance. Breeding for high-yielding cultivars combined with Ppr resistance is the most effective way of controlling Ppr of cocoa on the crops of growers with small holdings in Papua New Guinea.     

Purification and characterization of delta helicase from fetal calf thymus.

A DNA helicase (delta helicase) which partially copurifies with DNA polymerase delta has been highly purified from fetal calf thymus. delta helicase differs in physical and enzymatic properties from other eukaryotic DNA helicases described thus far. The enzyme has an apparent mass of 57 kDa by gel filtration and is associated with polypeptides of 56 and 52 kDa by SDS-polyacrylamide gel electrophoresis. Photo-cross-linking of the purified enzyme with [alpha-32P]ATP resulted in labeling of a polypeptide of approximately 58 kDa, suggesting that the active site is present on the larger polypeptide. Unwinding of a partial duplex requires a nucleoside triphosphate which can be either ATP or dATP but not a nonhydrolyzable analogue of ATP. Other ribo- and deoxyribonucleoside triphosphates have little or no activity as cofactors. delta helicase also has DNA-dependent ATPase activity which has a relatively low Km for ATP (40 microM). delta helicase binds to single-stranded DNA but has little or no affinity for double-stranded DNA or single-stranded RNA. Similar to replicative DNA helicases from prokaryotes and the herpes simplex virus type 1 helicase-primase, delta helicase translocates in the 5'-3' direction along the strand to which it is bound and preferentially unwinds DNA substrates with a forklike structure.