Effect of high pH on the spectral and catalytic properties of beef heart cytochrome oxidase

Incubation of cytochrome oxidase at high pH induces changes in several spectral properties. The optical Soret maximum shifts to longer wavelength, and there is an apparent loss in intensity of the 655-nm band, effects that are normally assigned either to a spin-state transition in cytochrome a3 or to a reduction of heme a. However, magnetic circular dichroism spectra show that cytochrome a3 remains high spin and that both cytochrome a and cytochrome a3 are oxidized. At the same time, there is the appearance of a low-spin signal indicative of hydroxide-imidazole coordination which we assign as arising from a structural transition at cytochrome a, rather than at cytochrome a3, as has been proposed previously. With longer incubation times, a new copper signal appears with electron paramagnetic resonance parameters markedly different from those obtained from copper centers which have undergone denaturation. Spin quantitation establishes that this new resonance does not arise from CuA and suggests that high pH breaks the magnetic coupling present at the cytochrome a3-CuB center. A significant proportion of cytochrome a3 may be converted to a low-spin thiolate during this process.     

Toward a unified theory of sexual mixing and pair formation.

Sexually transmitted diseases such as gonorrhea, syphilis, herpes, and AIDS are driven and maintained in populations by epidemiological and sociological factors that are not completely understood. One such factor is the way in which people mix sexually. In this paper, we outline a unified approach to modeling sexual mixing structures, where such structures are defined in terms of a set of axioms for a finite number of distinct groups of people. Theorems for homosexual, heterosexual, and arbitrary group mixing are presented, leading to a representation of all mixing structures defined by the axioms. The representation and its parameters are interpreted in terms of intergroup affinities for sexual mixing. The use of the approach in sexually transmitted disease modeling is discussed.     

Extensive variation in synonymous substitution rates in mitochondrial genes of seed plants

Background  

It has long been known that rates of synonymous substitutions are unusually low in mitochondrial genes of flowering and other land plants. Although two dramatic exceptions to this pattern have recently been reported, it is unclear how often major increases in substitution rates occur during plant mitochondrial evolution and what the overall magnitude of substitution rate variation is across plants.     

Platelet-activating factor secreted by DDAVP-treated monocytes mediates von willebrand factor release from endothelial cells

We have previously shown that although DDAVP (1-deamino-8-D-arginine vasopressin), a synthetic analogue of the natural hormone arginine vasopressin, does not directly promote release of vWf from human umbilical vein endothelial cells (ECs), enhanced release does occur when ECs were exposed to either monocytes or to supernatants recovered from DDAVP-treated monocytes. In the present study, we have found that exposure of monocytes to DDAVP did not increase secretion of interleukins (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF-α), growth factors G-CSF (granulocyte-), GM-CSF (granulocyte, monocyte-colony stimulating factor), prostaglandins (PG) E₂, PGF_2α, or PGI₂ or purine nucleotides such as ATP and ADP. However, increased levels of platelet-activating factor (PAF) were secreted by DDAVP-treated monocytes in a time- and dose-dependent manner that positively correlated with the enhancement in vWf release from ECs. Moreover, this effect could also be elicited when lipid extracts of these supernatants or purified PAF were added directly to ECs. This response could be inhibited with (±)-trans-2,5-Bis(3,4,5-trimethoxyphenyl)-1,3-dioxolane, a specific PAF receptor antagonist, when the ECs were exposed to supernatants from DDAVP-treated monocytes or to pure PAF. The present data indicate that enhanced secretion of PAF from monocytes is one mechanism whereby DDAVP can provoke release of vWf from ECs. © 1993 Wiley-Liss, Inc.