Electron spin relaxation of CuA and cytochrome a in cytochrome c oxidase. Comparison to heme, copper, and sulfur radical complexes

The method of continuous saturation has been used to measure the electron spin relaxation parameter T1T2 at temperatures between 10 and 50 K for a variety of S = 1/2 species including: CuA and cytochrome a of cytochrome c oxidase, the type 1 copper in several blue copper proteins, the type 2 copper in laccase, inorganic Cu(II) complexes, sulfur radicals, and low spin heme proteins. The temperature dependence and the magnitude of T1T2 for all of the species examined are accounted for by assuming that the Van Vleck Raman process dominates the electron spin-lattice relaxation. Over the entire temperature range examined, the relaxation of the type 1 coppers in six to seven times faster than that of type 2 copper, inorganic copper, and sulfur radicals, in spite of the similar g-anisotropies of these species. This result may indicate that the coupling of the phonon bath to the spin center is more effective in type 1 coppers than in the other complexes studied. The relaxation of CuA of cytochrome oxidase exhibits an unusual temperature dependence relative to the other copper complexes studied, suggesting that the protein environment of this center is different from that of the other copper centers studied and/or that CuA is influenced by a magnetic dipolar interaction with another, faster-relaxing paramagnetic site in the enzyme. A comparison of the saturation characteristics of the CuA EPR signal in native and partially reduced CO complexes of the enzyme also suggests the existence of such an interaction. The implications of these results with respect to the disposition of the metal centers in cytochrome oxidase are discussed.     

南瓜雌蕊与自花及远缘花粉的相互作用

南瓜柱头表面经去垢剂、蛋白酶及Con A处理后花粉不能萌发或花粉管生长受阻,Con A能专一地与柱头表面结合。柱头块加入培养液可促进花粉萌发。不同的远缘花粉授粉后在雌蕊不同部位受阻。在成熟南瓜雌蕊提取液中检测到血凝活性,凝集素可能参与雌蕊对远缘花粉的抑制。     

Developmentally regulated rearrangement and expression of genes encoding the T cell receptor-T3 complex

Human leukemic cells corresponding to the earliest identifiable stages of intrathymic T cell differentiation lack cell surface expression of the T cell receptor(TCR alpha/beta)-T3 complex but transcribe TCR beta mRNA from either germ-line configuration (1/13) or partially (DJ) or fully (VDJ) rearranged (12/13) genes. These cells do not produce TCR alpha mRNA, but do contain T3 delta and T3 epsilon mRNA and accumulate T3 polypeptides, primarily in the perinuclear envelope. Equivalent normal T cells isolated from thymus have a predominantly germ-line configuration of TCR beta but contain intracellular T3 proteins. T3 gene expression is therefore a very early event in T cell differentiation. TCR alpha chain production appears to be the limiting maturation-linked event in the transport, assembly, and cell surface membrane insertion of the TCR alpha/beta-T3 complex.     

七种云南地衣植物的化学成分

本文报道分属于三个科的七种云南产地衣植物的化学成分。这些植物是亚洲树发(Alectoria asiatica DR.)、沟树发(Alectoria sulcata Nyl.)、长茎松萝(Usnea longissimaAch.)、胡子松萝(Usnea comosa(Ach.)Rohl.)、林石蕊(Cladonia arbuscula(Rabh.)Rabh.)、砖孢发(Oropogon loxensis(Fee.)Th.Fr.)和卷梢雪花衣(Anaptychiaboryi(Fee.)Mass.)。根据光谱数据测定,其化学成分为:松萝酸(Usnic acid)(1),维任西酸(Virensic acid)(2),赤星衣酸乙酯(Ethyl haematommate)(3),瑞藏酸(Rhizonic acid)(4),赤星衣酸(Haematommic acid)(5),扁枝衣酸乙酯(Ethyleverninate)(6),黑茶渍素(Atranorin)(7)和泽屋萜(Zeorin)(8)。上述资料,对开发利用这些植物资源提供了科学依据。     

Collagen defects in lethal perinatal osteogenesis imperfecta.

Quantitative and qualitative abnormalities of collagen were observed in tissues and fibroblast cultures from 17 consecutive cases of lethal perinatal osteogenesis imperfecta (OI). The content of type I collagen was reduced in OI dermis and bone and the content of type III collagen was also reduced in the dermis. Normal bone contained 99.3% type I and 0.7% type V collagen whereas OI bone contained a lower proportion of type I, a greater proportion of type V and a significant amount of type III collagen. The type III and V collagens appeared to be structurally normal. In contrast, abnormal type I collagen chains, which migrated slowly on electrophoresis, were observed in all babies with OI. Cultured fibroblasts from five babies produced a mixture of normal and abnormal type I collagens; the abnormal collagen was not secreted in two cases and was slowly secreted in the others. Fibroblasts from 12 babies produced only abnormal type I collagens and they were also secreted slowly. The slower electrophoretic migration of the abnormal chains was due to enzymic overmodification of the lysine residues. The distribution of the cyanogen bromide peptides containing the overmodified residues was used to localize the underlying structural abnormalities to three regions of the type I procollagen chains. These regions included the carboxy-propeptide of the pro alpha 1(I)-chain, the helical alpha 1(I) CB7 peptide and the helical alpha 1(I) CB8 and CB3 peptides. In one baby a basic charge mutation was observed in the alpha 1(I) CB7 peptide and in another baby a basic charge mutation was observed in the alpha 1(I) CB8 peptide. The primary defects in lethal perinatal OI appear to reside in the type I collagen chains. Type III and V collagens did not appear to compensate for the deficiency of type I collagen in the tissues.     

Conformational and dynamic considerations in the design of peptide hormone analogs

Efforts to understand the chemical-physical basis for peptide hormone and neurotransmitter action requires integration of conformational parameters and biological properties. Since most peptide hormones are conformationally flexible, the question arises as to which of the manifold of conformations is of biological significance. In molecular terms, it is necessary to carefully distinguish chemical-physical features important to binding (the binding message) from those involved in transduction (the biological activity message). One approach to this involves the design, synthesis, and conformational analysis of semirigid hormone analogs. The distinction between binding and transduction can best be examined by evaluation of full biological profiles of partial agonists, antagonists, and analogs with prolonged biological activity. Using this multidisciplinary approach, we have prepared several semirigid [Pen¹]-oxytocin antagonist analogs and evaluated their conformational properties and biological activities. Specific conformational features can be related to inhibitory activities in several cases. On the basis of structure–activity relationships and conformational considerations, we have designed a series of conformationally restricted cyclic and acyclic analogs of the linear peptide α-melanotropin. Some of these peptides have exceptionally prolonged in vivo activity (weeks), and others exhibit superagonist potency (10,000 times the native hormone). We have evidence that potency and prolonged activity have different structural and conformational requirements. It is suggested that potency is primarily a function of receptor recognition (the binding message), whereas prolonged activity is related to transduction (the biological activity message).     

The sequence of the nucleotides at the alpha-sarcin cleavage site in rat 28 S ribosomal ribonucleic acid

The sequence of the 521 nucleotides at the 3' end of a rat 28 S rRNA gene was determined. The region encompasses the site of cleavage of 28 S rRNA by the cytotoxin alpha-sarcin. The toxin hydrolyzes a phosphodiester bond on the 3' side of a guanine residue 393 nucleotides from the 3' end. The alpha-sarcin domain is composed of a purine-rich sequence of 14 highly conserved nucleotides.     

A family of Saccharomyces cerevisiae repetitive autonomously replicating sequences that have very similar genomic environments

We have characterized a family of moderately repetitive autonomously replicating sequences (ARSs) in Saccharomyces cerevisiae. Restriction mapping, deletion studies and hybridization studies suggest that these ARSs, which are probably less than 350 base-pairs in size, share one common feature: each is located close to, but not within, a repetitive sequence (131) of approximately 10(3) to approximately 1.5 X 10(3) base-pairs in length. These ARSs can be divided into two classes (X and Y) by their sequence homology and genomic environments. Each of the class X ARSs is embedded within a repetitive sequence (X) of variable length (approximately 0.3 X 10(3) to approximately 3.75 X 10(3) base-pairs); each of the class Y ARSs is embedded within a highly conserved repetitive sequence (Y) of approximately 5.2 X 10(3) base-pairs in length. Both of these sequences are located directly adjacent to the 131 sequence.     

Organization of DNA sequences and replication origins at yeast telomeres

We have shown that the DNA sequences adjacent to the telomeres of Saccharomyces cerevisiae chromosomes are highly conserved and contain a high density of replication origins. The salient features of these telomeres can be summarized as follows. There are three moderately repetitive elements present at the telomeres: the 131 sequence (1 to 1.5 kb), the highly conserved Y sequence (5.2 kb), and the less conserved X sequence (0.3 to 3.75 kb). There is a high density of replication origins spaced about 6.7 kb apart at the telomeres. These replication origins are part of the X or the Y sequences. Some of the 131-Y repetitive units are tandemly arranged. The terminal sequence T (about 0.33 to 0.6 kb) is different from the 131, X, or Y sequences and is heterogeneous in length. The order of these sequences from the telomeric end towards the centromere is T-(Y-131)n-X-, where n ranges from 1 to no more than 4. Although these telomeric sequences are conserved among S. cerevisiae strains, they show striking divergence in certain closely related yeast species.