Exchange rates and numbers of annular lipids for the calcium and magnesium ion dependent adenosinetriphosphatase

A spin-labeled phospholipid is used to study lipid-protein interactions in the (Ca2+,Mg2+)-ATPase of sarcoplasmic reticulum from muscle. A novel null method is used to decompose composite electron spin resonance spectra into two components, characteristic of immobilized and mobile environments. Calculations based on a random mixing model suggest that protein-protein interactions will be relatively rare in these systems and that the immobilized lipid does not represent lipid trapped between proteins but rather represents annular phospholipid at the lipid-protein interface of the adenosinetriphosphatase. The apparent decrease in the amount of immobilized lipid with increasing temperature is shown to be consistent with lipid exchange between bulk and annulus, characterized by an exchange time of 10(-7) s at 37 degrees C. A minimum number of annular phospholipid sites of 32 and 22 are calculated at 0 and 37 degrees C, respectively.     

A complex biogeographic history of diversification in Neotropical lancehead pitvipers (Serpentes,Viperidae)

Based on the literature, we had predicted that the diversification within the Neotropical snake genus Bothrops occurred along a latitudinal gradient from north to south, with diversification into unoccupied niches through ecological opportunity, not correlated with geoclimatic events. Using a dated phylogeny and estimating likelihoods of ancestral states at cladogenesis events, we reconstructed ancestral areas and assessed major events of the diversification of Bothrops clades, and we also discuss systematic implications for this group. Based on the phylogeny we produced, B. lojanus was not considered as part of the genus Bothrops since the results recovered this species nested within the Bothrocophias clade. We infer that the diversification of the Miocene Bothrops pictus and Bothrops alternatus clades may be related to the uplift of the western slopes of the Andes and the Argentinian Patagonian Andes, respectively. The Pliocene Bothrops taeniatus and Bothrops osbornei clades may be related to the uplift of the eastern and northern Andes, respectively. The Plio-Pleistocene Bothrops neuwiedi clade may be related to the habitat transitions from a warmer and forested environment to a cooler and open landscape; the Bothrops jararaca (i.e. island endemic species) and Bothrops lanceolatus clades to over-water dispersal with island speciation; and Bothrops atrox clade to the appearance of the Panamanian land bridge. We found that a multitemporal and multidirectional history of diversification may be correlated with geoclimatic and dispersalist events. We argue that the vacant niche hypothesis by itself does not explain Bothrops diversification.     

The mechanism of action of the tetrapeptide Acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) in the control of haematopoietic stem cell proliferation

Abstract. The mechanism of action of the haemoregulatory tetrapeptide Acetyl-N-Ser-Asp-Lys-Pro (AcSDKP, Mr = 487 amu), was investigated using an in vitro assay of a murine high proliferative potential colony-forming cell (HPP-CFC) which responds to proliferation regulators of the haematopoietic stem cell population. AcSDKP had no direct inhibitory effect on the number, or the proportion in S phase, of the committed granulocyte-macrophage progenitor (GM-CFC), or cycling HPP-CFC populations. However, AcSDKP blocked the action of a stimulator of haematopoietic stem cell proliferation, preventing the switching of quiescent HPP-CFC into cell cycle. It would appear that AcSDKP exerts its inhibitory haemoregulatory role indirectly, by preventing stimulator action on haematopoietic stem cells.     

Training Primary Care Physicians in Flexible Sigmoidoscopy—Performance Evaluation of 17, 167 Procedures

The flexible fiber-optic sigmoidoscope is rapidly replacing the rigid sigmoidoscope in routine screening for colorectal cancer. This study was undertaken to evaluate the safety, usage pattern, and efficacy of fiber-optic sigmoidoscopy by evaluating the outcome of training and the results of procedures carried out by a group of primary care physicians. Of 1,153 participants in one-day flexible sigmoidoscopy workshops, 764 (66%) returned questionnaires evaluating their experiences following this training. Of these, 438 physicians had obtained a flexible sigmoidoscope, used it frequently, and had done a total of 17,167 examinations. The average time of scope usage was nine months. Although additional supervised training was suggested at the time of the workshop, 68% of physicians began doing flexible sigmoidoscopy without it. A total of 465 polyps and 153 cancers were detected by the study group for an overall detection rate of 2.7% for polyps and 0.9% for cancers. Four complications were reported. This study indicates that the technique of flexible sigmoidoscopy is readily learned, is diagnostically productive, and is reasonably safe in the hands of primary care physicians.