Enzyme immobilization using a cellulose-binding domain: properties of a beta-glucosidase fusion protein.

Using molecular genetic techniques, a fusion protein has been produced which contains the cellulose-binding domain (CBD) of an exoglucanase (Cex) from Cellulomonas fimi fused to a beta-glucosidase (Abg) from Agrobacterium sp. The CBD functions as an affinity tag for the simultaneous purification and immobilization of the enzyme on cellulose. Binding to cellulose was stable for prolonged periods at temperatures from 4 degrees C to at least 50 degrees C, at ionic strengths from 10 mM to greater than 1 M, and at pH values below 8. The fusion protein can be desorbed from cellulose with distilled water or at pH greater than 8. Immobilized enzyme columns of the fusion protein bound to cotton fibers exhibited stable beta-glucosidase activity for at least 10 days of continuous operation at temperatures up to 37 degrees C. At higher temperatures, the bound enzyme lost activity. The thermal stability of the fusion protein was greatly improved by immobilization. Immobilization did not alter the pH stability. Except for its ability to bind to cellulose, the properties of the fusion protein were virtually the same as those of the native enzyme.     

Atrial natriuretic factor R1 receptor from bovine adrenal zona glomerulosa: purification, characterization, and modulation by amiloride

The atrial natriuretic factor (ANF) R1 receptor from bovine adrenal zona glomerulosa was solubilized with Triton X-100 and purified 13,000-fold, to apparent homogeneity, by sequential affinity chromatography on ANF-agarose and steric exclusion high-performance liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining of the purified receptor preparation in the absence or presence of dithiothreitol revealed a single protein band of Mr 130,000. Affinity cross-linking of 125I-ANF to the purified receptor resulted in the labeling of the Mr 130,000 band. The purified receptor bound ANF with a specific activity of 6.8 nmol/mg of protein, corresponding to a stoichiometry of 0.9 mol of ANF bound/mol of Mr 130,000 polypeptide. Starting with 500 g of adrenal zona glomerulosa tissue, we obtained more than 500 pmol of purified receptor with an overall yield of 9%. The purified receptor showed a typical ANF-R1 pharmacological specificity similar to that of the membrane-bound receptor. The homogeneous Mr 130,000 receptor protein displayed high guanylate cyclase activity [1.4 mumol of cyclic GMP formed min-1 (mg of protein)-1] which was not stimulated by ANF. This finding supports the notion that the ANF binding and the guanylate cyclase activities are intrinsic components of the same polypeptide. Finally, the purified ANF-R1 receptor retained its sensitivity to modulation by amiloride, suggesting the presence of an allosteric binding site for amiloride on the receptor protein.     

Influence of hypoxemia and respiratory acidosis on the plasma kinetics and tissue distribution of digoxin in the conscious dog

The aim of the present study was to investigate the influence of hypoxemia combined with respiratory acidosis on the kinetics of digoxin in conscious dogs. One group of three beagles was exposed to air and 7 days later to 10% O2, 10% CO2, and 80% N2. In a second group of three dogs, the order of exposure to the two atmospheric conditions was reversed. The dogs received 25 micrograms/kg digoxin and blood and urine samples were collected over the next 29 h. At the conclusion of the second treatment, the dogs were sacrificed to determine digoxin concentrations in the left ventricle, liver, renal cortex, and skeletal muscle. Digoxin total body clearance increased from 6.2 +/- 0.9 in control to 9.0 +/- 1.0 mL X min-1 X kg-1 in hypoxemic and hypercapnic dogs (p less than 0.05). The digoxin apparent volume of distribution at steady state (Vss) was increased in the dogs with hypoxemia and hypercapnia (11.63 +/- 1.11 vs. 8.62 +/- 0.41 L/kg in the controls, p less than 0.05). As a consequence the digoxin plasma half-life remained unchanged (18.6 +/- 1.5 h in hypoxemic and hypercapnic dogs versus 20.1 +/- 2.8 h in the controls). In dogs with hypoxemia and hypercapnia, the ratio of tissue to plasma digoxin concentrations tended to increase in the liver, in the renal cortex, and in the left ventricle and remained unchanged in the left hind leg muscle. In vitro studies showed that the digoxin total binding to erythrocyte membranes was slightly increased in the dogs with hypoxemia and hypercapnia, resulting from an increase in the apparent intrinsic association constant for digoxin (p less than 0.003). It is concluded that hypoxemia combined with respiratory acidosis changes digoxin disposition in the conscious dog and is the cause of a digoxin redistribution into the tissues.     

Dietary factors affecting the urinary mutagenicity assay system. I. Detection of mutagenic activity in human urine following a fried beef meal

Studies have been conducted to determine whether the mutagens in fried beef ingested by human subjects are excreted in the urine. Urine samples were collected from individuals on liquid or regular diets before and after a fried beef meal. The mutagenic activity of the samples was tested in the Ames Salmonella/microsome assay system. The results showed that in individuals on liquid diets, most of the urinary mutagenic activity is recovered within 2-6 h after consuming a fried beef meal. In one individual tested, mutagenic activity was found in urine samples obtained 6-15 h after the fried beef meal. No mutagenic activity was detected in any of the urine samples obtained 15-24 h following the meal. In individuals on a regular diet, however, mutagenic activity was frequently observed in urine samples obtained 16-24 h following the fried beef meal, although the mutagenic activity was not as great as that in the preceding 16 h. It appears that the mutagenic agents generated by the frying of beef are ingested, absorbed, and excreted by the human body in biologically detectable quantities. These results suggest that subjects should abstain from fried beef at least one day prior to and during urine mutagenicity screening.     

Dietary factors affecting the urinary mutagenicity assay system. II. The absence of mutagenic activity in human urine following consumption of red wine or grape juice

The mutagenic activity of urine samples from nonsmoking individuals before and after the consumption of either red wine or grape juice was determined. Urine samples collected from individuals on liquid or regular diets were concentrated using XAD-2 resin. No mutagenic activity of urine concentrates was detected with Salmonella tester strains TA98 or TA100 with or without microsomal activation. The addition of 1000 units of beta-glucuronidase into the agar overlay did not show any mutagenic activity. The mutagens in red wine and grape juice, however, were extracted using the XAD-2 column. Concentrates of urine samples spiked with either of the two extracts exhibited mutagenic activity.     

Proton nuclear magnetic resonance assignments of thyroid hormone and its analogues

1H NMR data of a series of thyroid hormone analogues, e.g., thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), 3,5-diiodothyronine (3,5-T2), 3',5'-diiodothyronine (3',5'-T2), 3-monoidothyronine (3-T1), 3'-monoiodothyronine (3'-T1), and thyronine (TO) in dimethylsulfoxide (DMSO) have been obtained on a 300 MHz spectrometer. The chemical shift and coupling constant are determined and tabulated for each aromatic proton. The inner tyrosyl ring protons in T4, T3, and 3,5-T2 have downfield chemical shifts with respect to those of the outer phenolic ring protons. Four-bond cross-ring coupling has been observed in all the monoiodinated rings. However, this long-range coupling does not exist in T4, diiodinated on both rings, and T0, containing no iodines on the rings. There is no evidence that at 30 degrees C these iodothyronines have any motional constraint in DMSO solution. In addition to identification of the hormones, the potential use of some characteristic peaks as probes in binding studies is discussed.     

Preparation of bovine blood coagulation factors X1 and X2

A method is described for the preparation of both Factor X1 and Factor X2 from citrated bovine blood. The proteins from the plasma were first adsorbed on barium citrate by adding barium chloride solution. The precipitate formed was stirred with citrate/NaOH pH 6.9 buffer; barium and other clotting factors were removed by adding ammonium sulphate (up to 30% saturation) to the suspension. The Factor X was then precipitated by 65% ammonium sulphate, after resolution in citrate buffer chromatographed on DEAE-Sephadex and purified by rechromatography on DEAE-Sephadex and DEAE-Sepharose, respectively. This yielded Factor X1 and Factor X2 with respective purifications of about 16 000 and 24 000-fold that of the plasma. The apparent molecular mass of both Factor X1 and Factor X2 was 55 kDa as estimated by the sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Factor X2 had a higher specific biological activity of about 340 000 units/mg compared to that of Factor X1 of about 230 000 units/mg.     

31P and19F NMR studies of glycophorin-reconstituted membranes: Preferential interaction of glycophorin with phosphatidylserine

Summary Glycophorin A, a major glycoprotein of the erythrocyte membrane, has been incorporated into small unilamellar vesicles composed of a variety of pure and mixed phospholipids. Nuclear spin labels including³¹P and¹⁹F have been used at natural abundance or have been synthetically incorporated in lipids to act as probes of lipid-protein interaction. Interactions produce broadening of resonances in several cases and it can be used to demonstrate preferential interaction of certain lipids with glycophorin.³¹P and¹⁹F probes show a strong preferential interaction of glycophorin with phosphatidylserine over phosphatidylcholine. There is some evidence that interactions are more pronounced at the inner surface of the bilayer and these results are rationalized in terms of the asymmetric distribution of protein and lipid.