Reversible inhibition of the proton pump bacteriorhodopsin by modification of tyrosine 64.

Five mol of lysine per mol of bacteriorhodopsin were modified with methylacetimidate. This treatment did not inactivate bacteriorhodopsin but prevented all lysines from subsequent reaction with diazotized sulfanilic acid. This reaction predominantly modified tyrosine 64 and light-induced proton translocation was abolished. Reduction of the mono(p-azobenzene sulfonic acid) tyrosine 64 to the corresponding 3-amino derivative with sodium dithionite led to complete reactivation of the proton translocation activity of bacteriorhodopsin. The relative location of tyrosines 26 and 64 and the COOH terminus on the two surfaces of the purple membrane was determined by incorporation into phospholipid vesicles, subsequent modification, and proteolytic treatment. The results obtained support the models proposed by Engelmann et al. (Engelman, D. M., Henderson, R. McLauchlan, A. D., and Wallace, B. A. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 2023-2027) and by Ovchinnikov et al. (Ovchinnikov, Yu. A., Abdulaev, N. G., Feigina M. Yu., Kiselev A. V., and Lobanov, N. A. (1979) FEBS Lett. 100, 219-224). Tyrosine 64 is located on the extracellular side of the membrane, whereas tyrosine 26 and the COOH terminus are located on the cytoplasmic side. Because specific nitration of tyrosine 26 also leads to inactivation of bacteriorhodopsin (Lemke, H. D., and Oesterhelt, D. (1981) Eur. J. Biochem. 115, 595-604), the results obtained demonstrate that amino acid residues located on both surfaces of the purple membrane are involved in proton translocation.

Rapid colorimetric assay for acetaminophen without salicylate or phenylephrine interference.

A simple rapid, and economical procedure is presented for the quantitative determination of acetaminophen in serum. Acetaminophen is extracted into solvent, and, when back-extracted into base, is simultaneously reacted with Folin-Ciocalteau reagent to form a colored complex. The potential interference of bilirubin is eliminated by treatment with p-diazobenzene sulfonic acid. Results obtained with this method agree with those obtained by "high-pressure" liquid chromatography.

The role of platelet surface proteins reacting with heterologous antibodies.

Platelets were labeled with surface-labelling agents which identified up to six platelet membrane proteins. Three of these labelled proteins were recognised by a specific anti-platelet membrane serum by immunoprecipitation. Affinity fractionation of platelets with insolubilised IgG obtained from the anti-platelet membrane serum indicated a greater reaction between the antiserum and the platelet surface. Fab fragments from the antiserum inhibited ristocetin-induced aggregation of platelets and partially inhibited collagen-induced aggregation but did not affect ADP aggregation. Crossed immunoelectrophoresis of platelets using the anti-platelet membrane serum showed that the antiserum was specific for platelet membranes.

Orientation of complex III in the yeast mitochondrial membrane: labeling with [125I] diazobenzenesulfonate and functional studies with the decyl analogue of coenzyme Q as substrate.

Mitochondria (or mitoplasts) and submitochondrial particles from yeast were treated with [125I] diazobenzenesulfonate to label selectively proteins exposed on the outer or inner surface of the inner mitochondrial membrane. Polyacrylamide gel analysis of the immunoprecipitates formed with antibodies against Complex III or cytochrome b revealed that the two core proteins and cytochrome b were labeled in both mitochondria and submitochondrial particles, suggesting that these proteins span the membrane. Cytochrome c1 and the iron sulfur protein were labeled in mitochondria but not in submitochondrial particles, suggesting that these proteins are exposed on the cytosolic side of the inner membrane. The steady-state reduction of cytochromes b and c1 was determined with succinate and the decyl analogue of coenzyme Q as substrates. Addition of the coenzyme Q analogue to mitochondria caused reduction of 15-30% of ;the total dithionite-reducible b and 100% of the cytochrome c1: Addition of the coenzyme Q analogue to submitochondrial particles led to the reduction of 70% of the total dithionite-reducible cytochrome b but insignificant amounts of cytochrome c1. A model to explain the topography of Complex III in the inner membrane is proposed based on these results.

Quantitative changes in adipocyte plasma membrane in response to nutritional manipulations.

The effects of changes in adipocyte size and the effects of nutritional manipulations on the quantity of plasma membrane per adipocyte were investigated. A method for estimating the quantity of plasma membrane was developed based on the specific labeling of adipocyte plasma membrane protein with the nonpermeable labeling agent 125I-labeled diazotized diiodosulfanilic acid. By studying rats (ranging in age from 50 to 125 days) fed a standard laboratory chow or a low fat diet or a high fat diet, a wide range of mean fat cell sizes was obtained. It was found that as the volume of the fat cell increased, the amount of plasma membrane increased in a linear fashion and that this linear relationship had the same slope whether the size of the adipocyte increased slowly with age or rapidly in response to a high fat diet. In contrast, fasting for up to 3 days caused a marked decrease in the mean volume of the adipocytes, but either no change or much less change in the amount of plasma membrane per cell than would have been predicted from the linear relationship between adipocytes, but either no change or much less change in the amount of plasma membrane per cell than would have been predicted form the linear relationship between adipocyte volume and amount of plasma membrane per cell obtained with fed rats, i.e., adipocytes from fasted rats contain more plasma membrane per cell than do fat cells of the same size from fed rats. Neither feeding a high fat diet nor fasting caused detectable changes in the protein and lipid composition of the adipocyte plasma membrane.

The organization of formate dehydrogenase in the cytoplasmic membrane of Escherichia coli.

The arrangement of the proton-translocating formate dehydrogenase of the anaerobic respiratory chain of Escherichia coli within the cytoplasmic membrane was examined by direct covalent modification with non-membrane-permeant reagents. Three methods were employed, lactoperoxidase-catalysed radioiodination, labelling with diazotized [125I] di-iodosulphanilic acid and labelling with diazobenzene [35S] sulphonate. All three procedures yield consistent with the view that the two larger subunits of the enzyme, Mr 110000 and 32000, both occupy transmembranous locations within the membrane. In each case the modification of the Ca2+ or Mg2+-activated F1-ATPase was monitored, and all reagents employed correctly located this enzyme at the cytoplasmic face of the membrane. A procedure involving agglutination with specific antibodies is described which appears to fractionate membrane vesicles of mixed orientation into two populations, one with the same membrane orientation as that of spheroplasts and the other opposite orientation.

Respiratory burst enzyme in human neutrophils. Evidence for multiple mechanisms of activation.

Alteration of the surface of human neutrophils with the nonpenetrating, protein-inactivating agent p-diazobenzenesulfonic acid (DASA) was found to prevent activation of the respiratory burst by some stimuli, but not others. Production of superoxide anion (O2-) stimulated by concanavalin A or the chemotactic peptide formyl-methionyl-leucyl-phenylalanine FMLP was inhibited by DASA pretreatment, whereas O2- production stimulated by phorbol myristate acetate (PMA), sodium fluoride. or the ionophore A23187 was not inhibited by DASA. Pretreatment with DASA inhibited oxygen uptake stimulated by FMLP, but not oxygen uptake stimulated by PMA. DASA reproducibly inhibited activities of two known surface enzymes Mg++-ATPase and alkaline phosphatase, by 45-55% and 60-70%, respectively. The inhibition by DASA of O2- production did not appear to be caused by interference with binding of the affected stimuli, since pretreatment with DASA did not inhibit release of the lysosomal enzymes lysozyme and myeloperoxidase induced by concanavalin A or FMLP. Membrane-rich particulate fractions from neutrophils have been shown to contain NADPH-dependent oxidative activity that is presumably responsible for the phagocytosis-associated respiratory burst of intact cells. The PMA-activated enzyme was susceptible to inhibition of directly exposed to DASA in this particulate fraction. These findings suggest that more than one mechanism exists for activation of the respiratory burst oxidase in human neutrophils, and that the neutrophil possesses at least one oxidase that is not an ectoenzyme.

Studies on the sidedness of the human red blood cell membrane: preparation of stable azo-erythrocytes.

Para-diazobenzenesulfonic acid (DBSA), a non-penetrating compound, which reacts with proteins of the external surface of intact cells, was used for the preparation of AZO-erythrocytes. When coupling of p-diazobenzenesulfonic acid to human red blood cells was carried out in phosphate-buffered saline (PBS), the cells lysed within one hour, before the completion of the reaction. Elimination of sodium chloride from the reaction mixture allowed the completion of coupling by prolonging the survival of red blood cells in he diazonium salt from one hour to three hours. The survival of human erythrocytes could be further prolonged to seven hours by carrying out coupling in the presence of cyclic 3',5'-guanosine monophosphate (cGMP). Azo-erythrocytes prepared in the absence of cyclic GMP and washed free of the diazonium salt lysed in phosphate-buffered saline, but remained stable for hours in isosmotic phosphate buffers devoid of sodium chloride ions. Under identical conditions, azo-erythrocytes prepared in the presence of cyclic GMP remained stable for two days and were suited for studies on the functional and structural aspects of red blood cell membrane.

Labelling of intestinal brush border membrane proteins in vivo using diazotised[125I]iodosulfanilic acid.

Membrane proteins of the intestinal brush border were labelled in vivo by intraluminal injection of diazotised [125I]iodosulfanilic acid, a highly polar molecule. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of brush border membranes labelled in this manner showed 20 protein bands, 11 of which contained significant radioactivity. The most heavily labelled proteins had molecular weights greater than 150000, indicating that they were the most exposed to the intestinal lumen. Little radioactivity was detected in proteins with molecular weights of less than 94000. The majority of these smaller proteins were likely to have been brush border core proteins. The evidence that diazotised [125I]iodosulfanilic acid bound primarily to brush border membrane proteins when administered in this way, was: (a) the specific activity of brush border proteins was up to 3-fold greater than that of total cell particulate proteins (pelleted by 27000 x g from mucosal homogenates); (b) principal peaks in the gel radioactivity profile of total cell particulate proteins corresponded to the most heavily labelled proteins of the isolated brush border membrane; and (c) brush border core proteins showed minimal radioactivity in vivo, but considerably higher radioactivity when brush border membranes were labelled in vitro. A small amount of label was absorbed across the intestinal mucosa. However, secondary labelling of brush border proteins by this absorbed label was minimal, since the specific activity of brush border proteins in jejunum adjacent to the labelled loop was only 0.22% of the level for those proteins in the labelled segment. Since this technique did not affect the cellular morphology, enzyme activity or biochemical integrity of the membrane, it should prove useful as a means of accurately studying in vivo turnover rates of brush border membrane proteins.

Diazobenzenesulphonate selectively abolishes stimulation of glucuronidation by UDP-N-acetylglucosamine.

1. Basal rates of glucuronidation of oestrone (guinea pig) or of 4-nitrophenol (rat or guinea pig) were not significantly altered in sealed liver microsomal vesicles, treated with the membrane-impermeant protein-modifying agent diazobenzenesulphonate at 0.5-1.0 mM. 2. Contrarily, diazobenzenesulphonate abolished the normal stimulation of glucuronidation by UDP-N-acetylglucosamine. 3. Ultrasonication to increase microsomal permeability activated glucuronidation by 680-750% and permitted significant inhibition by diazobenzenesulphonate. 4. These findings are consistent with a model wherein glucuronyltransferases are embedded in the luminal leaflet of the endoplasmic reticulum and access of UDP-glucuronic acid to the transferases is facilitated by transmembrane carriers, which are stimulated by UDP-N-acetylglucosamine and are available to diazobenzenesulphonate; ultrasonication serves to permit access of diazobenzenesulphonate to glucuronyltransferases themselves, resulting in inhibition of their activity.

Structure of the cytochrome c oxidase complex: labeling by hydrophilic and hydrophobic protein modifying reagents.

Beef heart cytochrome c oxidase has been reacted with [35S]diazobenzenesulfonate ([35S]DABS), [35S]-N-(4-azido-2-nitrophenyl)-2-aminoethylsulfonate ([35S]NAP-taurine), and two different radioactive arylazidophospholipids. The labeling of the seven different subunits of the enzyme with these protein modifying reagents has been examined. DABS, a water-soluble, lipid-insoluble reagent, reacted with subunits II, III, IV, V, and VII but labeled I or VI only poorly. The arylazidophospholipids, probes for the bilayer-intercalated portion of cytochrome c oxidase, labeled I, III, and VII heavily and II and IV lightly but did not react with V or VI. NAP-taurine labeled all of the subunits of cytochrome c oxidase. Evidence is presented that this latter reagent reacts with the enzyme from outside the bilayer, and the pattern of labeling with the different hydrophilic and hydrophobic labeling reagents is used to derive a model for the arrangement of subunits in cytochrome c oxidase.