PubMed · 4863938
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
C M Weiss. 1967. Water pollution.. https://pubmed.ncbi.nlm.nih.gov/4863938/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Tonoplast membrane fractions were isolated from beetroot (Beta vulgaris) using a refined method of preparation which significantly improved the yield of active tonoplast H(+)-ATPase, and electron microscopy showed these fractions to be a preparation of small vesicles, of diameter 500 nm to 50 nm and a minor fraction consisting of mainly tubular membrane structures of diameter 5 nm and length up to 1 micron. The stability of the tonoplast H(+)-ATPase was assessed in the presence of many biological detergents, using a linked assay. The addition of detergent to tonoplast membranes generally led to an increase in ATPase activity, and activity was maintained in a wide range of both non-ionic and zwitterionic detergents. Using the non-ionic detergent dodecyl maltoside, the tonoplast H(+)-ATPase was partially purified using ion-exchange chromatography on an HPLC system. Very high rates of ATP hydrolysis were recorded in these fractions. The purified membranes behaved as expected in the presence of known activators and inhibitors. An unexpected observation, however, was that low concentrations of vanadate could significantly increase the rate of H(+)-ATPase activity.
The platelet integrin, glycoprotein IIb-IIIa (GPIIb-IIIa), is a calcium-dependent heterodimer that binds fibrinogen, von Willebrand factor, and fibronectin after platelet activation. We examined GPIIb-IIIa alone and bound to these ligands by electron microscopy after rotary shadowing with platinum/tungsten. We found, as observed previously, that in the presence of detergent and 2 mM Ca2+, GPIIb-IIIa consists of an 8 x 12-nm globular head with two 18-nm flexible tails extending from one side. We also found that in the presence of EDTA, GPIIb-IIIa dissociates into two similar comma-shaped subunits, each containing a portion of the globular head and a single tail. Using monoclonal antibodies to GPIIb, GPIIIa, and the GPIIb-IIIa heterodimer, we found that the tails contained the carboxyl termini of each subunit, while the nodular head was composed of amino-terminal segments of both subunits. Electron microscopy of GPIIb-IIIa bound to fibrinogen revealed a highly specific interaction of the nodular head of GPIIb-IIIa with the distal end of the trinodular fibrinogen molecule and with the tails of GPIIb-IIIa extended laterally at an angle of approximately 98 degrees with respect to the long axis of fibrinogen. When a GPIIb-IIIa was bound to each end of a single fibrinogen, the tails were oriented to opposite sides of fibrinogen, enabling fibrinogen to bridge two adjacent platelets. Electron microscopy of GPIIb-IIIa bound to fibronectin revealed GPIIb/IIIa-binding sites approximately two-thirds of the distance from the amino terminus of each end of the fibronectin molecule, while GPIIb-IIIa was found to bind to von Willebrand factor protomers along a rod-like region near the central nodule of the molecule.
The membrane nature of squalene oxide cyclase from Saccharomyces cerevisiae was investigated by comparing properties of the enzyme recovered from both microsomes and the soluble fraction of the yeast homogenate. The "apparent soluble" form and microsomal form of the enzyme were both stimulated by the presence of mammalian soluble cytoplasm and corresponded to one another in response to detergents Triton X-100 and Triton X-114. The observed strong dependence of the enzyme activity on the presence of detergents and the behavior of the enzyme after Triton X-114 phase separation were peculiar to a lipophilic membrane-bound enzyme. A study of the conditions required to extract the enzyme from microsomes confirmed the lipophilic character of the enzyme. Microsomes, exposed to ipotonic conditions to remove peripheral membrane proteins, retained most of the enzyme activity within the integral protein fraction. Quantitative dissociation of the enzyme from membranes occurred only if microsomes were treated with detergents (Triton X-100 or octylglucoside) at concentrations which alter membrane integrity. The squalene oxide cyclase was purified 140 times from yeast microsomes by (a) removal of peripheral proteins, (b) extraction of the enzyme from the integral protein fraction with octylglucoside, and (c) separation of the solubilized proteins by DEAE Bio-Gel A chromatography. Removal of the peripheral proteins seemed to be a key step necessary for obtaining high yields.