Radiation chemistry of a multicomponent aqueous system relevant to chemistry of cometary nuclei

Summary We have examined a water-dominated multicomponent system after irradiation in the multimegarad dose range with gamma rays from a⁶⁰Co source at both 77 and 310 K. The constituents were simple organic compounds in the proportions in which they appear in a dense interstellar cloud: HCN/CH₃OH/CH₃CN/C₂H₅CN/HCOOH=10.60.20.10.05. The total amounts were adjusted to correspond to a carbon to nitrogen ratio of 1.8 and a water content of about 50% in a cometary nucleus where the dust to volatiles ratio is 1; the total amount of CN-bearing compounds was taken to correspond to 0.4% of the cometary mass. In experiments at 310 K about 40 radiolytic products are identified, among them aldehydes and amino and carboxylic acids. Abundant polymeric material (M_w up to 80,000 daltons) is formed. The basic aspects of radiolysis of the liquid system are present also at 77 K, although at radiation-chemical yields that are lower by one to two orders of magnitude. We have considered the relevance of the present findings to the chemistry of a liquid-water core and the icy layers of a cometary nucleus.     

Radiation chemistry of an aqueous solution of glycine: compounds of interest to chemical evolution studies

Summary We have examined the radiolysis of an O₂-free aqueous solution of glycine at absorbed doses of⁶⁰Co gamma-radiation of up to 20 Mrad. At least 20 compounds are formed during radiolysis, among them several amino acids, an oligoamine, and the nitrogen-free polymers (M_w28,000 daltons). When dicyandiamide is present in the solution of glycine, various nitrogen-containing products, including some polymers (M_w12,000 daltons), are synthesized along with radiolytic products of glycine; polyglycines are not formed. We have determined the radiation-chemical yields of radiolytic-product formation and of decomposition of glycine, and have considered possible free-radical reactions leading to the radiation-induced changes observed.     

An oxygen-evolving complex with a simple subunit structure - ‘a water-plastoquinone oxidoreductase” - from the thermophilic cyanobacterium Synechococcus sp.

An oxygen-evolving complex has been highly purified from the thermophilic cyanobacterium Synechococcus sp. The complex, which reproducibly showed 5 major polypeptide bands of 47, 40, 35, 30 and 9 kDa on SDS-polyacrylamide gel electrophoresis and contained 3.2 Mn per Q_A, had an oxygen-evolving activity of 300–400 μmol/mg chl per h in the presence of 5 mM MnCl₂; or CaCl₂. The complex most likely represents a minimum functional unit of the photosynthetic oxygen evolution.     

A new mechanism for altering chromosome number during karyotype evolution

Summary A new mechanism for changing chromosome numbers (preserving the fundamental number of long chromosome arms) during karyotype evolution is suggested. It includes: 1) Occurrence of individuals heterozygous for two interchanges between different arms of three chromosomes (a metacentric and two acrocentric ones). 2) Formation in heterokaryotypes of multivalents during meiosis between the chromosomes involved in the interchanges and their unchanged homologues. 3) Mis-segregation of chromosomes from these multivalents resulting in hypoploid (n-1) and hyperploid (n+1) simultaneously instead of euhaploid gametes. 4) Fusion of n-1 or n+1 gametes which gives rise to (zygotes and) individuals representing homokaryotypes with changed number of chromosomes (2n+2 or 2n-2), but preserves (as compared to the parental karyotypes) the number of long chromosome arms. Under definite conditions, chromosome numbers of the progeny may be changed by this process in both directions (upwards and downwards). The mechanism is free of the difficulties associated with the explanation for such changes by direct Robertsonian interchanges (see Discussion), which are usually considered to be responsible for such alterations in chromosome number. The above-mentioned process has been experimentally documented in Vicia faba and it probably also occurred naturally within the Vicia sativa group.     

Similarities in the genomic sequence and coat protein structure of plant virsuses

The genomic sequences of several RNA plant viruses including cucumber mosaic virus, brome mosaic virus, alfalfa mosaic virus and tobacco mosaic virus have become available recently. The former two viruses are icosahedral while the latter two are bullet and rod shaped, respectively in particle morphology. The non-structural 3a proteins of cucumber mosaic virus and brome mosaic virus have an amino acid sequence homology of 35% and hence are evolutionarily related. In contrast, the coat proteins exhibit little homology, although the circular dichroism spectrum of these viruses are similar. The non-coding regions of the genome also exhibit variable but extensive homology. Comparison of the brome mosaic virus and alfalfa mosaic virus sequences reveals that they are probably related although with a much larger evolutionary distance. The polypeptide folds of the coat protein of three biologically distinct isometric plant viruses, tomato Bushy stunt virus, southern bean mosaic virus and satellite tobacco necrosis virus have been shown to display a striking resemblance. All of them consist of a topologically similar 8-standard β-Barrel. The implications of these studies to the understanding of the evolution of plant viruses will be discussed.     

Crystal structure of subtilisin complexed with its trapped substrateStreptomyces subtilisin inhibitor—Protein-protein interaction and evolution of serine proteinases and their proteinaceous inhibitors

The complex of a bacterial alkaline serine proteinase, subtilisin BPN’, with its proteinaceous inhibitorStreptomyces subtilisin inhibitor is unique in several respects, compared with other similar complexes containing serine proteinases of trypsin family. In addition to the usual antiparallelβ-sheet involving P₁-P₃ residues of the inhibitor, P₄-P₆ residues form antiparallelβ-sheet with a previously unnoticed chain segment (the ‘S4-6 site’) of subtilisin. The ‘S4-6 site’ does not exist in serine proteinases of trypsin family, whether of mammalian or microbial origin. Global induced-fit movement seems to occur on the ‘trapped substrate’Streptomyces subtilisin inhibitor: a channel-like structure in SSI remote from the contact region becomes about 2 Å wider upon complexing with subtilisin. Main role of the secondary contact region ofStreptomyces subtilisin inhibitor seems to support the reactive site loop (primary contact region). Steric homology for the two contact regions is so high between the inhibitors ofStreptomyces subtilisin inhibitor family and those of pancreatic secretory trypsin inhibitor-ovomucoid inhibitor family that it seems to favour a divergent evolution and to support the general notion as to the relationship of prokaryotic and eukaryotic genes put forwarded by Doolittle(Nature (London),272, 581, 1978).     

Prediction and comparison of the secondary structure of legume lectins

Secondary structure prediction for the 4 legume lectins: Concanavalin A, soybean agglutinin, favabean lectin and lentil lectin, was done by the method of Chou and Fasman. This prediction shows that these four lectins fall into a structurally distinct class of proteins, containing high amounts of β-sheet and β-turns. There is a notable similarity in the gross structure of these proteins; all four of them contain about 40–50% of β-sheet, 35–45 % β-turn and 0–10% of α-helix. When the secondary structure of corresponding residues in each pair of these lectins was compared, there was a striking similarity in the Concanavalin A-soybean agglutinin and favabean lectin-lentil lectin pairs, and considerably less similarity in the other pairs, suggesting that these legume lectins have probably evolved in a divergent manner from a common ancestor. A comparison of the predicted potential β-turn sites also supports the hypothesis of divergent evolution in this class of lectins.     

A new pollen type,C-banded and fluorochrome counterstained chromosomes,and evolution inGuatteria and related genera (Annonaceae)

Guatteria, Guatteriopsis, Guatteriella andHeteropetalum share the same conspicuous pollen type which is new for theSpermatophyta. It is zonoaperturate with a folded aperture region and an extremely reduced exine. First chromosome counts and karyotype analyses forGuatteriopsis (4 species investigated) andGuatteriella (1 species) are identical with those ofGuatteria (19 species seen): 2n = 28. The genome is characterized by diploidization and partly telocentric chromosomes. Sequentially Giemsa C- and fluorochrome banded chromosomes and interphase nuclei are described. The cuticular folding pattern is distinct forHeteropetalum only. Growth forms and ecology are reported for many species. The evolutionary pattern of theGuatteria group is discussed and compared with other genera and families.     

How can quantum mechanics of material evolution be possible?: Symmetry and symmetry-breaking in protobiological evolution

Material self-assembly as a self-organizing process is always accompanied by symmetry-breaking in the material configuration. Self-sequencing of amino acids during their thermal polymerization has lost a certain property of permutation symmetry that was observed in the mixture of free amino acids. The evolutionary precursor state is more symmetrical about its internal material configuration and more degenerate due to the multitude of the indistinguishable individuals. The evolution proceeds in the direction along which the degeneracy in the internal states dissolves owing to the symmetry-breaking originating in material flow equilibrium of open material aggregates. Protobiological information is latent in the material system which is highly symmetrical and highly degenerate in its internal states. Evolution of matter is an endogenous process in which the earlier symmetric property is lost and less degenerate states are approached. Quantum-mechanically, the generation of protobiological information is due to the symmetry-breaking of the Hamiltonian originating in the interaction with the exterior through material flow, in contrast to the Schrödinger equation which preserves a symmetry and the associated invariants.     

Phosphoglucose isomerase isozymes in teleostean fishes from the Arabian Gulf

Two phosphoglucose isomerases (PGI) with different electrophoretic mobilities have been found in all groups of teleostean fishes studied, with the exception of the Clupeomorpha. PGI proved to be a good taxonomic criterion to differentiate members of the Nemipteridae, Sciaenidae, Platycephalidae and Stromateidae from the other teleost families.