PubMed · 531449
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B Charbonnel. 1979-10-11. [Hints for the practitioner].. https://pubmed.ncbi.nlm.nih.gov/531449/
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Purified adrenocortical microsomal cytochromes P-45017 alpha,lyase and P-450C21 were reconstituted with and without NADPH-cytochrome P-450 reductase in phosphatidylcholine-phosphatidylethanolamine-phosphatidylserine vesicles at a lipid to P-450 ratio of 35 (w/w) by cholate dialysis procedures. Trypsinolysis revealed that a considerable part of each P-450 molecule is deeply embedded in the lipid bilayer, on the basis of the observation of no detectable digestion for P-45017 alpha,lyase and the proteolysis-resistant membrane-bound heavy fragments for P-450C21. Rotational diffusion was measured in proteoliposomes and adrenocortical microsomes by observing the decay of absorption anisotropy, r(t), after photolysis of the heme-CO complex. Analysis of r(t) was based on a "rotation-about-membrane normal" model. The absorption anisotropy decayed within 1-2 ms to a time-independent value r3. Coexistence of a mobile population with an average rotational relaxation time phi of 138-577 microseconds and immobile (phi > or = 20 ms) populations of cytochrome P-450 was observed in both phospholipid vesicles and microsomes. Different tilt angles of the heme plane from the membrane plane were determined in proteoliposomes to be either 47 degrees or 63 degrees for P-45017 alpha,lyase from [r3/r(0)]min = 0.04 and either 38 degrees or 78 degrees for P-450C21 from [r3/r(0)]min = 0.19, when these P-450s were completely mobilized by incubation with 730 mM NaCl. Very different interactions with the reductase have been observed for the two P-450s in proteoliposomes. In the presence of the reductase, the mobile population of cytochrome P-450C21 was increased significantly from 79% to 96% due to dissociation of P-450 oligomers.(ABSTRACT TRUNCATED AT 250 WORDS)
Many avian species of the North American Sonoran desert, e.g., the black-throated sparrow, Amphispiza bilineata, cactus wren, Campylorhynchus brunneicapillus, and curve-billed thrasher, Toxostoma curvirostre, can potentially breed from March/April to August. It is possible that, at least in summer, intense heat and aridity may have inhibitory effects on breeding by precipitating a stress response. Stress typically results in a rise in secretion of adrenocorticosteroid hormones that then inhibit reproduction by suppressing release of gonadal hormones. However, we found that plasma levels of corticosterone were not higher during summer, compared with winter, even in 1989 when summer temperatures were higher than normal. In June 1990, temperatures were also above normal and soared to the highest level recorded in Arizona (50 degrees C). Plasma levels of corticosterone during June were high in black-throated sparrows, but less so in two other species (Abert's towhee, Pipilo aberti, and Inca dove, Scardafella inca) found in more shady riparian and suburban habitat with constant access to water. The adrenocortical response to stress (as measured by the rate of corticosterone increase following capture) was reduced in the hottest summer months in black-throated sparrows, cactus wrens, and curve-billed thrashers, but less so in Abert's towhee an Inca dove. These data suggest that at least some birds breeding in the open desert with restricted access to water are able to suppress the classical adrenocortical response to stress. The response is then reactivated in winter after breeding has ceased. It is possible that this stress modulation may allow breeding to continue despite severe heat. Analysis of plasma from these species indicated that the apparent modulation of the adrenocortical response to stress was not an artifact of reduced affinity or capacity of corticosterone binding proteins.
Vascular endothelial growth factor (VEGF), also known as vascular permeability factor or vasculotropin, is a recently characterized endothelial-specific mitogen which is angiogenic in vivo. Here we demonstrate that VEGF is angiogenic in vitro: when added to microvascular endothelial cells grown on the surface of three-dimensional collagen gels, VEGF induces the cells to invade the underlying matrix and to form capillary-like tubules, with an optimal effect at approximately 2.2nM (100ng/ml). When compared to basic fibroblast growth factor (bFGF) at equimolar (0.5nM) concentrations, VEGF was about half as potent. The most striking effect was seen in combination with bFGF: when added simultaneously, VEGF and bFGF induced an in vitro angiogenic response which was far greater than additive, and which occurred with greater rapidity than the response to either cytokine alone. These results demonstrate that like bFGF, VEGF induces an angiogenic response via a direct effect on endothelial cells, and that by acting in concert, these two cytokines have a potent synergistic effect on the induction of angiogenesis in vitro. We suggest that the synergism between VEGF and bFGF plays an important role in the control of angiogenesis in vivo.