A possible energetic role of mineral surfaces in chemical evolution

The postulated roles of clays and other minerals in chemical evolution and the origin of life are reconsidered in terms of the interaction of these minerals with penetrating sources of energy such as ionizing radiation and mechanical stress. This interaction, including such facets as excitation, degradation, storage, and transfer, is considered here with regard to its profound potential for altering the capabilities of minerals to serve both as substrates for prebiological chemistry and as inorganic prototypic life forms. The interaction of minerals and energy in relationship to surface chemistry is discussed in terms of the spectroscopic properties of minerals, the interaction of energy with condensed phases, some commonly accepted concepts of heterogeneous catalysis in the absence of electronic energy inputs, and some commonly accepted and novel means by which surface activity might be enhanced in the presence of energy inputs.An estimation is made of the potential contribution of two poorly characterized prebiotic energy sources, natural radioactive decay and triboelectric energy. These estimates place a conservative lower limit on their prebiotic abundance. Also some special properties of these energy sources, relative to solar energy, are pointed out which might give them particular suitability for driving reactions occurring under geological conditions.Skeletal support for this broadly defined framework of demonstrated and potential relationships between minerals, electronic excitation, and surface reactivity, as applied to chemical evolution, is provided from the results of our studies on 1/1 clays. We have discovered and partially characterized a number of novel luminescent properties of these clays, that indicate energy storage and transfer processes in clays. These luminescent properties are interpreted in relationship to the electron spin resonance phenomena, to provide a basis for estimating the potential significance of energy storage and transduction in monitoring or driving clay surface chemistry.Consideration of the electronic structure of abundant minerals in terms of band theory and localized defect centers provides a predictive theoretical framework from which to rationalize the capacity of these materials to store and transduce energy. The bulk crystal is seen as a collecting antenna for electronic energy, with the defect centers serving as storage sites.The clay properties produced by isomorphic substitution appear to be intimately associated with all of the life-mimetic chemical processes that have been attributed to clays. It appears sensible to postulate that the energetic properties of these substitutional defect centers may also be influential in these biomimetic processes: the promotion of surface reactions, storage of information, replication with transfer of information, and asymmetric separation of electrical charges, as well as their more recently hypothesized roles in energy storage and transduction. The identity of the sites implicated in all of the biomimetic functions of clays as well as their capacity for energy storage is seen to offer significant potential for coupling these functions to an environmental energy source. A yet more specific and experimentally testable hypothesis is offered for a new biomimetic process performed by clays. This hypothesis is that energy stored near isomorphically substituted sites provides the energetic basis for the coupled transport of electrical charge and/or electronic energy through the clay layer, which operates via environmental activation of electron/hole mobility. This is to say that mobility of charge/electronic excitation between defect centers serves as the basis for a primordial inorganic electron transport chain.     

Mapping of epitopes, glycosylation sites, and complement regulatory domains in human decay accelerating factor.

Decay accelerating factor (DAF, CD55) is a glycophospholipid-anchored membrane protein that protects cells from complement-mediated damage by inhibiting the formation and accelerating the decay of C3/C5 convertases. DAF deletion mutants lacking each of the four short consensus repeats (SCR) or the serine/threonine-rich region (S/T) were created by site-directed mutagenesis. These deletion mutants were expressed by stable transfection in Chinese hamster ovary cells for the purpose of mapping important structural and functional sites in DAF. The epitopes on DAF for 16 murine mAb were mapped by immunoprecipitation studies as follows: SCR1, 6; SCR2, 3; SCR3, 3; SCR4, 3; S/T, 1. Testing of 13 mAb showed complete blocking of DAF function only by 1C6 and 1H4, both directed at SCR3. The single N-linked glycosylation site was confirmed at a location between SCR1 and SCR2, and the multiple O-linked oligosaccharides were localized to the S/T region. Functional activity of DAF mutants was assessed by the ability of these transfected constructs to protect Chinese hamster ovary cells from cytotoxicity induced by rabbit antibody plus human complement. Removal of SCR1 had no effect on DAF function, but individual deletion of SCR2, SCR3, or SCR4 totally abolished DAF function. Surprisingly, deletion of the S/T region totally abrogated DAF function, but this could be restored by a fusion construct placing the four SCR domains of DAF onto the HLA-B44 molecule, implying that the O-glycosylated S/T region serves as an important but nonspecific spacer projecting the DAF functional domains above the plasma membrane. Overall, the creation of DAF deletion mutants has elucidated important structure-function relations in the DAF molecule.     

EVOLUTIONARY GENETICS OF TWO SIBLING SPECIES,DROSOPHILA SIMULANS AND D. SECHELLIA

Drosophila simulans and D. sechellia are sibling species, the former cosmopolitan and the latter restricted to the Seychelles Islands. We used classical genetic analysis to measure the numbers and effects of genes responsible for reproductive isolation and morphological differences in male genitalia between these species. At least five loci are responsible for male sterility in hybrids, with the strongest effects produced by at least two genes on the X chromosome. At least three (and probably four) loci are responsible for the interspecific difference in the size of the posterior process of the male genital arch. These genetic results, as well as the pattern of morphological divergence between the species, show several parallels with the divergence between D. simulans and its other island relative, D. mauritiana. We also present the DNA sequence of a 4.5 kilobase region containing the alcohol dehydrogenase (Adh) locus of D. sechellia, and combine this with previous data to reconstruct the phylogenies of the three species and their more distant relative D. melanogaster. Both D. mauritiana and D. sechellia are very closely related to D. simulans. Although most phylogenies show the two island species to be independent offshoots of the D. simulans lineage (with D. sechellia the more recent), the branch points are too close to make this conclusion unambiguous. The genetic and evolutionary parallels between the simulans/mauritiana and the simulans/sechellia divergences may therefore represent either a striking evolutionary convergence or a close common ancestry of the island species. A comparison of Adh alleles within species shows that the divergence among them may be almost as large as among alleles from different species. We conclude that many of the nucleotide differences among these species actually represent polymorphisms within common ancestors. It may be difficult to build accurate phylogenies using only a single DNA sequence from each species.     

Ectopic Cushing's syndrome in cloacogenic carcinoma of the anal canal: a case demonstrating APUD characteristics

A patient found to have ectopic Cushing's syndrome three months after surgical resection of cloacogenic carcinoma of the anal canal was studied with serial plasma cortisol and ACTH measurements. The effects of therapy on plasma ACTH and cortisol levels were noted. An autopsy was performed immediately after death and liver metastatic tumor tissue was assayed for "small" ACTH, "big" ACTH, PTH, and alpha sub-unit of hCG, Clinical Cushing's syndrome was observed along with nonsuppressible plasma cortisol level. Plasma ACTH only reached the highest normal level but tumor ACTH ("small"), "big" ACTH, alpha sub-unit and PTH were markedly elevated. It was concluded that a case of classic cloacogenic carcinoma of the anal canal produced ectopic Cushing's syndrome. Elevated tumor alpha sub-unit and PTH were not associated with appreciable biologic activity. Ectopic Cushing's syndrome in this disease may imply poorer prognosis.     

A study of the mortality and fecundity of Haemonchus contortus in sheep following experimental infections.

The regulation of the fecundity and mortality of H. contortus in sheep was examined using a series of mathematical models. Six-month-old Dorset crossbred lambs were infected once only with various doses of infective H. contortus larvae (500-20,000 larvae). Parasite mortality was found to be an increasing linear function of the magnitude of the initial infection over the range of doses examined. Parasite fecundity was found to remain constant over the intensity and duration of the infection. The average fecundity for H. contortus at the time of slaughter was found to be 7037 eggs per female worm per day. There was no evidence of time-dependent changes in fecundity or density-dependent regulation of fecundity.     

Immunological identification and distribution of dissimilatory heme cd1 and nonheme copper nitrite reductases in denitrifying bacteria.

Polyclonal antibodies were used to identify heme or copper nitrite reductases in the following groups: 23 taxonomically diverse denitrifiers from culture collections, 100 numerically dominant denitrifiers from geographically diverse environments, and 51 denitrifiers from a culture collection not selected for denitrification. Antisera were raised against heme nitrite reductases from Pseudomonas aeruginosa and Pseudomonas stutzeri and against copper nitrite reductase from Achromobacter cycloclastes. Nitrite reductases were identified by Western immunoblot. Diethyldithiocarbamate, which specifically inhibits copper nitrite reductases, was used to confirm the immunological characterization and determine which type was present in strains nonreactive with any antiserum. For groups in which the type of nitrite reductase has not been previously described, we found that Alcaligenes eutrophus, Bacillus azotoformans, Bradyrhizobium japonicum, Corynebacterium nephridii, and Rhizobium spp. contained copper nitrite reductase, while Aquaspirillum itersonii, Flavobacterium spp., and Pseudomonas fluorescens contained heme nitrite reductase. Heme nitrite reductases dominated, regardless of soil type or geographic origin. They occurred in 64 and 92%, respectively, of denitrifiers in the numerically dominant and nonselected collections. The two nitrite reductase types were mutually exclusive in individual bacteria, but both appeared in different strains from the Alcaligenes and Pseudomonas genera. The heme type predominated in Pseudomonas strains. The heme-type nitrite reductase appeared more conserved if judged by similarities in molecular weights and immunological reactions. The Cu type was found in more taxonomically unrelated strains and varied in molecular weight and antiserum recognition.     

The evolutionary genetics of speciation.

The last decade has brought renewed interest in the genetics of speciation, yielding a number of new models and empirical results. Defining speciation as ''the origin of reproductive isolation between two taxa'', we review recent theoretical studies and relevant data, emphasizing the regular patterns seen among genetic analyses. Finally, we point out some important and tractable questions about speciation that have been neglected.