Biological membranes provide selective barriers to a number of molecules and gases. However, the factors that affect permeability to gases remain unclear because of the difficulty of accurately measuring gas movements. To determine the roles of lipid composition and the aquaporin 1 (AQP1) water channel in altering CO 2 flux across membranes, we developed a fluorometric assay to measure CO 2 entry into vesicles. Maximal CO 2 flux was ϳ1000-fold above control values with 0.5 mg/ml carbonic anhydrase. Unilamellar phospholipid vesicles of varying composition gave widely varying water permeabilities but similar CO 2 permeabilities at 25°C. When AQP1 purified from human red blood cells was reconstituted into proteoliposomes, however, it increased water and CO 2 permeabilities markedly. Both increases were abolished with HgCl 2 , and the mercurial inhibition was reversible with -mercaptoethanol. We conclude that unlike water and small nonelectrolytes, CO 2 permeation is not significantly altered by lipid bilayer composition or fluidity. AQP1 clearly serves to increase CO 2 permeation, likely through the water pore; under certain circumstances, gas permeation through membranes is protein-mediated.
ABSTRACr A method is described for the retrieval of streptavidin from the culture broth of Streptomyces avidinii. The key step in this procedure is the adsorption of streptavidin from culture concentrates to an affinity column in which iminobiotin is attached to AH-Sepharose 4B. This column binds streptavidin at pH 11 and releases the protein at pH 4. The recovery of streptavidin is practically quantitative. The pH dependence of the iminobiotin-avidin affinity, discovered by Green [Green, N. M. (1I) Biochem. 1. 101, 774-7791, has thus found practical application. The streptavidin bound 4.07 1 0.02 mol of [14C]biotin per mol and was essentially homogeneous as judged by disc and slab gel electrophoresis. Streptavidin was extensivey succinoylated without loss of biotin-binding capacity. The observations that 12SI-labeled streptavidin and I15I-labeled succinoylstreptavidin are retained by iminobiotin-AH-Sepharose 4B columns at pH 7.5 and are eluted at pH 4.0 provides a convenient purification method for these iodinated proteins. The technique employed for the retrieval of streptavidin is generally applicable to the isolation of iminobiotinylated molecules.In recent communications (1, 2) we proposed a scheme for the labeling of peptide and protein hormones involving the noncovalent attachment of 125I-labeled avidin of high specific radioactivity to biotinylated hormones. To test this idea a procedure was developed for labeling avidin with 1251 to high specific radioactivity st2 mCi/nmol; 1 Ci = 3.7 X 1010 bec.-querels. The labeled pHPP-avidint bound avidly to rat liver plasma membranes and was not displaceable by unlabeled avidin. Clearly 125I-pHPP-avidin was not a suitable label for biotinylinsulin. Because we suspected that the basic nature of avidin (isoelectric point 10.5) could contribute to its affinity for the essentially negatively charged plasma membranes, we subjected pHPP-avidin to extensive succionylation with succinic anhydride. This modification did not significantly alter the binding affinity for biotin, but the 125I-labeled Suc-pHPPavidint bound less firmly to the plasma membranes and was displaceable by unlabeled Suc-pHPP-avidin. With The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.
A characteristic defect occurs in rat and human hepatocellular carcinoma (HCC) resulting in a loss of function of the vitamin K-dependent enzyme gamma-glutamyl-carboxylase in the tumor but not in the underlying liver. This causes the secretion of elevated levels of the immature or des-gamma-carboxylated form of prothrombin, which is used as a marker of HCC. We investigated whether, using the defined conditions of growing HCC cell lines in tissue culture, addition of the naturally occurring vitamins K1 or K2 or the synthetic vitamin K3 could influence the secretion of immature prothrombin. We found that vitamins K1, K2 and K3 all suppressed the secretion of immature prothrombin into the tissue culture medium. Vitamins K2 and K3 were also found to inhibit growth of the HCC cell line, in an apparently nontoxic and reversible manner. The influence of the vitamins K on the expression of some genes related to vitamin K action was examined and compared with that of another growth inhibitor, TGF beta 1 protein. The vitamins K were found to increase the expression of prothrombin and carboxylase messenger RNA and c-myc messenger RNA, but had no effects on the expression of TGF beta 1 messenger RNA. By contrast, TGF beta 1 increased TGF beta 1 messenger RNA levels, but had no effects on the other genes, suggesting a different pathway. The previously studied vitamin K3-mediated inhibition of growth was antagonized by the addition of catalase to the culture medium, but the inhibitory effects of vitamin K2 were not antagonized.(ABSTRACT TRUNCATED AT 250 WORDS)
Using three antisera to oxytocin (OT Pitt Ab-1, OT Pitt Ab-2, and TOR OT Ab), we found comparable levels of OT in response to infant suckling and during infusion of synthetic OT, and identical standard curves with biological and synthetic standards of OT. Pitt Ab-1, but not Pitt Ab-2 or TOR OT Ab, measured increased OT in response to estrogen. Using an arginine vasotocin RIA (TOR AVT Ab), we found an increase in AVT immunoreactivity after estrogen treatment. Mean basal OT levels measured with OT Pitt Ab-2 in plasma of men [0.75 +/- 0.06 (+/- SEM) microU/ml] and women (0.8 +/- 0.09 microU/ml) were lower than OT measured with Pitt Ab-1 (1.7 +/- 0.09 microU/ml in men and 1.7 +/- 0.07 microU/al in women; P less than 0.001). Mean OT measured with Pitt Ab-2 in the plasma of women given estrogen chronically (0.8 +/- 0.04 microU/ml) and acutely (0.6 +/- 0.15 microU/ml) were not significantly different from basal levels. OT levels measured with Pitt Ab-1 in the same samples were 4.6 +/- 0.5 and 4.3 +/- 0.5 microU/ml, respectively, both significantly increased from basal levels (P less than 0.001) and significantly higher than OT measured with Pitt Ab-2 (P less than 0.001). Mean OT measured with Pitt Ab-1 in the plasma of pregnant women was 8.6 +/- 1.02 microU/ml, significantly higher than OT measured with Pitt Ab-2 (1.0 +/- 0.3 microU/ml; P less than 0.001). Men given 25 mg diethylstilbestrol had significant increases in OT measured with Pitt Ab-1 and in AVT measured with TOR AVT (P less than 0.01), but not in OT measured with Pitt Ab-2. Plasma from a man given diethylstilbestrol was prepared for high performance liquid chromatography and applied to a C18 muBondapak reverse phase column. The plasma contained two peaks of immunoreactivity detected as OT with Pitt Ab-1 and as AVT using TOR AVT Ab. The material was not detected by Pitt Ab-2 or TOR OT Ab and did not coelute with standards of OT, AVT, or AVP. Pregnancy plasma, thioglycolic acid, chymotrypsin, and trypsin reduced Pitt Ab-1, Pitt Ab-2, and TOR OT immunoreactivity of synthetic OT. The percent recovery of OT immunoreactivity was not significantly different with Pitt Ab-1 vs. Pitt Ab-2. A novel peptide, which is increased in response to administered estrogen, is present in human plasma and is detected by some antisera to OT and AVT. The observation explains the wide variability in OT levels in the estrogen-primed state and provides a new mechanism to study estrogen-related physiology and pathophysiology.
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