Triton X-100-4 M urea as an extraction medium for membrane proteins. I. Purification of chloroplast cytochrome b559

Oxygen-induced changes in the redox state of the cytochrome b559 in photosystem II depend on the integrity of the Mn cluster

The effect of oxygen and anaerobiosis on the redox properties of Cyt b(559) was investigated in PSII preparations from spinach with different degree of disintegration of the donor side. Comparative studies were performed on intact PSII membranes and PSII membranes that were deprived of the 18-kDa peripheral subunit (0.25 NaCl washed), the 18- and 24-kDa peripheral subunits (1 M NaCl washed), the 18-, 24- and 33-kDa peripheral subunits (1.2 M CaCl(2) washed), Cl depleted and after complete depletion of the Mn cluster (Tris washed). In active PSII centers, about 75% of Cyt b(559) was found in the high-potential form and the rest in the intermediate potential form. With decomposition of the donor side, the intermediate potential form started to dominate, reaching more than 90% after Tris treatment. The oxygen-dependent conversion of the intermediate potential form of Cyt b(559) into the low-potential and high-potential forms was only observed after treatments that directly affect the Mn cluster. In PSII membranes, deprived of all three extrinsic subunits (CaCl(2) treatment), 21% of the intermediate potential form was converted into the low-potential form and 14% into the high-potential form by the removal of oxygen. In Tris-washed PSII membranes, completely lacking the Mn cluster, this conversion amounted to 60 and 33%, respectively. In intact PSII membranes, the oxygen-dependent conversion did not occur. The possible physiological role of this oxygen-dependent behavior of the Cyt b(559) redox forms during the assembly/photoactivation cycle of PSII is discussed.

Extinction coefficients of cytochromes b559 and c550 of Thermosynechococcus elongatus and Cyt b559/PS II stoichiometry of higher plants

"Reduced minus oxidized" difference extinction coefficients Deltavarepsilon in the alpha-bands of Cyt b559 and Cyt c550 were determined by using functionally and structurally well-characterized PS II core complexes from the thermophilic cyanobacterium Thermosynechococcus elongatus. Values of 25.1+/-1.0 mM(-1) cm(-1) and 27.0+/-1.0 mM(-1) cm(-1) were obtained for Cyt b559 and Cyt c550, respectively. Anaerobic redox titrations covering the wide range from -250 up to +450 mV revealed that the heme groups of both Cyt b559 and Cyt c550 exhibit homogenous redox properties in the sample preparation used, with E(m) values at pH 6.5 of 244+/-11 mV and -94+/-21 mV, respectively. No HP form of Cyt b559 could be detected. Experiments performed on PS II membrane fragments of higher plants where the content of the high potential form of Cyt b559 was varied by special treatments (pH, heat) have shown that the alpha-band extinction of Cyt b559 does not depend on the redox form of the heme group. Based on the results of this study the Cyt b559/PSII stoichiometry is inferred to be 1:1 not only in thermophilic cyanobacteria as known from the crystal structure but also in PSII of plants. Possible interrelationships between the structure of the Q(B) site and the microenvironment of the heme group of Cyt b559 are discussed.

Differing involvement of sulfoquinovosyl diacylglycerol in photosystem II in two species of unicellular cyanobacteria

Sulfoquinovosyl diacylglycerol (SQDG) is involved in the maintenance of photosystem II (PSII) activity in Chlamydomonas reinhardtii[Minoda, A., Sato, N., Nozaki, H., Okada, K., Takahashi, H., Sonoike, K. & Tsuzuki, M. et al. (2002) Eur. J. Biochem.269, 2353-2358]. To understand the spread of the taxa in which PSII interacts with SQDG, especially in cyanobacteria, we produced a mutant defective in the putative sqdB gene responsible for SQDG synthesis from two cyanobacteria, Synechocystis sp. PCC6803 and Synechococcus sp. PCC7942. The mutant of PCC6803, designated SD1, lacked SQDG synthetic ability and required SQDG supplementation for its growth. After transfer from SQDG-supplemented to SQDG-free conditions, SD1 showed decreased net photosynthetic and PSII activities on a chlorophyll (Chl) basis with a decrease in the SQDG content. Moreover, the sensitivity of PSII activity to 3-(3,4-dichlorophenyl)-1,1-dimethylurea and atrazine was increased in SD1. However, SD1 maintained normal amounts of cytochrome b559 and D1 protein (the subunits comprising the PSII complex) on a Chl basis, indicating that the PSII complex content changed little, irrespective of a decrease in the SQDG content. These results suggest that the role of SQDG is the conservation of the PSII properties in PCC6803, consistent with the results obtained with C. reinhardtii. In contrast, the SQDG-null mutant of PCC7942 showed the normal level of PSII activity with little effect on its sensitivity to PSII herbicides. Therefore, the difference in the SQDG requirement for PSII is species-specific in cyanobacteria; this could be of use when investigating the molecular evolution of the PSII complex.

In vitro assembly of a beta2 cytochrome b559-like complex from the chemically synthesised beta-subunit encoded by the Synechocystis sp. 6803 psbF gene

The alpha- and beta-subunits of cytochrome b559 encoded by the psbE and psbF gene, respectively, are essential components of photosystem II. The exact structure of this cytochrome is not yet known. The beta-subunit of the Synechocystis sp. 6803 cytochrome b559 complex was synthesised by means of solid-phase peptide synthesis. Under reducing conditions, two beta-peptide molecules could be assembled specifically with one haem to form a beta2 cytochrome b559-like complex. The spectral properties and the midpoint redox potential (48+/-5 mV) of the in vitro assembled beta2 cytochrome are nearly identical to those of the low potential form of the native cytochrome b559.

A novel gene, pmgA, specifically regulates photosystem stoichiometry in the cyanobacterium Synechocystis species PCC 6803 in response to high light

Previously, we identified a novel gene, pmgA, as an essential factor to support photomixotrophic growth of Synechocystis species PCC 6803 and reported that a strain in which pmgA was deleted grew better than the wild type under photoautotrophic conditions. To gain insight into the role of pmgA, we investigated the mutant phenotype of pmgA in detail. When low-light-grown (20 microE m(-2) s(-1)) cells were transferred to high light (HL [200 microE m(-2) s(-1)]), pmgA mutants failed to respond in the manner typically associated with Synechocystis. Specifically, mutants lost their ability to suppress accumulation of chlorophyll and photosystem I and, consequently, could not modulate photosystem stoichiometry. These phenotypes seem to result in enhanced rates of photosynthesis and growth during short-term exposure to HL. Moreover, mixed-culture experiments clearly demonstrated that loss of pmgA function was selected against during longer-term exposure to HL, suggesting that pmgA is involved in acquisition of resistance to HL stress. Finally, early induction of pmgA expression detected by reverse transcriptase-PCR upon the shift to HL led us to conclude that pmgA is the first gene identified, to our knowledge, as a specific regulatory factor for HL acclimation.

Characterization of a D1-D2-cyt b-559 complex containing 4 chlorophyll a/2 pheophytin a isolated with the use of MgSO4

A D1-D2-cyt b-559 complex containing 4 chlorophyll alpha, 1 beta-carotene and 1 cytochrome b-559 per 2 pheophytin a has been isolated from spinach with 30% yield using a Q-Sepharose Fast-Flow anion-exchange column equilibrated with 0.1% Triton X-100, 10 mM MgSO4 and 50 mM Tris-HCl (pH 7.2). The preparation was then stabilized with 0.1% dodecyl-beta-D-maltoside. This method gave a yield 10 times higher than that using a Fractogel TSK-DEAE 650(S) column equilibrated with 0.1% Triton X-100, 30 mM NaCl and 50 mM Tris-HCl (pH 7.2). The PS II RC complex was characterized using absorption and fluorescence spectroscopy at 277 and 77 K. A selective reversible bleaching under reducing conditions with maximum at 682 nm, associated with pheophytin a reduction, and light-induced absorption differences with a lifetime of 1.0 ms, ascribed to the triplet state of P680 were measured and indicated that the isolated D1-D2-cyt b-559 complex is active in charge separation. The results are compared with the data obtained for a PS II RC preparation containing 6 chlorophyll alpha, 2 beta-carotene and 1 cyt b-559 per 2 pheophytin a.

Changes in composition of membrane proteins accompanying the regulation of PS I/PS II stoichiometry observed with Synechocystis PCC 6803

Changes in composition of membrane proteins in Synechocystis PCC 6803 induced by the shift of light regime for photosynthetic growth were studied in relation to the regulation of PS I/PS II stoichiometry. Special attention was paid to the changes in abundance of proteins of PS I and PS II complexes. Composition was examined using a LDS-PAGE and a quantitative enzyme immunoassay. Abundance of PsaA/B polypeptides and the PsaC polypeptide of the PS I complex, on a per cell basis, increased under the light regime exciting preferentially PS II and decreased under the light regime exciting mainly PS I. Similar changes were observed with polypeptides of 18.5, 10 and 8.5 kDa. The abundance of other proteins associated with membranes, including PsbA polypeptide of the PS II complex, was fairly constant irrespective of light regime. These results are consistent with our previous observations with other strains of cyanophytes (Anabaena variabilis M2 and Synechocystis PCC 6714) that PS I is the variable component in changes in PS I/PS II stoichiometry in response to changing light regimes for photosynthesis.

Pigment stoichiometry of a newly isolated D1-D2-Cyt b559 complex from the higher plant Beta vulgaris L

Two D1-D2-Cyt b559 complexes with different pigment stoichiometry were isolated from the higher plant B. vulgaris. The procedures for isolating both complexes only differed in the washing time of the DEAE column with 50 mM Tris-HCl, pH 7.2, 0.05% Triton X-100 and 30 mM NaCl. When the column was washed until the eluate had an absorbance of 0.01 at 670 nm, the isolated D1-D2-Cyt b559 complex presented a pigment stoichiometry of 6 chlorophyll a, 2 beta-carotene, and 1 cytochrome b559 per 2 pheophytin a. In contrast, when the column was exhaustively washed until the eluate reached an absorbance of 0.005 at 670 nm, the complex had a stoichiometry of 4 chlorophyll a, 1 beta-carotene, and 1 cytochrome b559 per 2 pheophytin a. We think that the former stoichiometry corresponds to that of the native D1-D2-Cyt b559 complex. Moreover, both preparations showed 2 mol of pheophytin a per 1 mol of reaction center protein.

Rapid and simple isolation of pure photosystem II core and reaction center particles from spinach

Pure and active oxygen-evolving PS II core particles containing 35 Chl per reaction center were isolated with 75% yield from spinach PS II membrane fragments by incubation with n-dodecyl-β-D-maltoside and a rapid one step anion-exchange separation. By Triton X-100 treatment on the column these particles could be converted with 55% yield to pure and active PS II reaction center particles, which contained 6 Chl per reaction center.

Electron-transfer reactions in manganese-depleted photosystem II

We have used flash-detection optical and electron paramagnetic resonance spectroscopy to measure the kinetics and yield per flash of the photooxidation of cytochrome b559 and the yield per flash of the photooxidation of the tyrosine residue YD in Mn-depleted photosystem II (PSII) membranes at room temperature. The initial charge separation forms YZ+ QA-. Following this, cytochrome b559 is oxidized on a time scale of the same order and with the same pH dependence as is observed for the decay of YZ+; under the conditions of our experiments, the decay of YZ+ is determined by the lifetime of YZ+ QA-. In order to explain this observation, we have constructed a model for electron donation in which YZ+ and P680+ are in redox equilibrium and cytochrome b559 and YD are oxidized via P680+. Using our results, together with data from earlier investigations of the kinetics of electron transfer from YZ to P680+ and charge recombination of YZ+ QA-, we have obtained the first global fit for electron donation in Mn-depleted PSII that accounts for the data over the pH range from 5 to 7.5. From these calculations, we have obtained the intrinsic rate constants of all the electron-donation reactions in Mn-depleted PSII. These rate constants allow us to calculate the free energy difference between YZ+ P680 and YZ P680+, which is found to increase by 47 +/- 4 mV/pH from pH 5 to 6 and is observed to increase more slowly per pH unit for pH greater than 6. An important conclusion of our experimental work is that the rates of photooxidation of cytochrome b559 and YD are determined by the lifetime of the oxidizing equivalent on YZ/P680. Extension of our model to oxygen-evolving PSII samples leads to the prediction that the kinetics and yields of electron donation from cytochrome b559 and YD to P680+ will depend on the S2- or S3-state lifetime.

On the structure and function of cytochrome b-559

A sumary of biochemical, biophysical, and molecular biological data is presented which led to the identification of two different polypeptides (α and β, MW=9.16 and 4.27 kDa) in the cytochrome b-559 protein. The presence of a single His residue on each polypeptide, and the conclusion from spectroscopy that the heme coordination must be bis-histidine led to an obligatory requirement for coordination of a single heme through a heme cross-linked dimer. This structure does not have a precedent among soluble or membrane bound cytochromes. The possible participation of the cytochrome in the pathway of photoactivation is discussed.

Isolation and purification of membrane-bound cytochrome b-560 from photosynthetic bacterium Chromatium vinosum

A membrane-bound cytochrome of the b-type (cytochrome b-560) was success-fully purified from chromatophores of the photosynthetic purple sulfur bacterium Chromatium vinosum by treatment with sodium cholate, sodium deoxycholate, sodium thiocyanate, and bacterial alkaline protease (EC 3·4·21·14) followed by gel filtration.The purified cytochrome b-560 showed the absorption maxima at 279, 412.5 and 533 nm in the oxidized form, and 427, 530 and 560 nm in the reduced form. Reduced-minus-oxidized difference millimolar absorption coefficient was 14.0 for a wavelength pair, 560 minus 540 nm.Isolated cytochrome b-560 was electrophoretically homogeneous, and its minimal molecular weight was estimated to the 13,000 by SDS polyacrylamide gel electrophoresis.The midpoint potential at pH 8.0 was -110mV, and was not dependent on the ambient pH in the pH range of 6.8 to 8.8.

Maternal inheritance of cytochrome f in interspecific Nicotiana hybrids

Cytochrome f has been purified to homogeneity, as judged by polyacrylamide gel electrophoresis, from the leaves of Nicotiana tabacum, Nicotiana glutinosa and their reciprocal hybrids. The cytochrome was extracted from chloroplast membranes by sonication in 2% Triton X-100 and 4M urea and was subsequently purified by acetone precipitation and chromatography on Ultrogel AcA 22 in the presence of cholate and on Sephadex G-200 in the presence of sodium dodecylsulphate. The purified cytochrome had a molecular weight of 32,700 determined by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate. A difference in the primary structure of cytochrome f from N. tabacum and N. glutinosa was detected by ion-exchange chromatography of the products of trypsin hydrolysis. Cytochrome f from N. tabacum contained an additional peptide not present in the cytochrome fom N. glutinosa. This additional peptide was present in the cytochrome from N. tabacum female x N. glutinosa male, but not in the cytochrome from N. glutinosa female x N. tabacum male, indicating a maternal mode of inheritance of the primary structure of cytochrome f. This suggests an extranuclear, probably chloroplast, location for the genetic information for cytochrome f.

Synthesis of thylakoid membrane proteins by chloroplasts isolated from spinach. Cytochrome b559 and P700-chlorophyll a-protein

Intact chloroplasts, purified from spinach leaves by sedimentation in density gradients of colloidal silica, incorporate labeled amino acids into at least 16 different polypeptides of the thylakoid membranes, using light as the only source of energy. The thylakoid products of chloroplast translation were visualized by subjecting membranes purified from chloroplasts labeled with [35S]methionine to electrophoresis in high-resolution, SDS-containing acrylamide gradient slab gels and autoradiography. The apparent mol wt of the labeled products ranged from less than 10,000 to greater than 70,000. One of the labeled products is the apoprotein of the P700-chlorophyll a-protein (CPI). The CPI apoprotein is assembled into a pigment-protein complex which is electrophoretically indistinguishable from the native CPI complex. Isolated spinach chloroplasts also incorporate [3H]leucine and [35S]methionine into cytochrome b559. The radioactive label remains with the cytochrome through all stages of purification: extraction of the thylakoid membranes with Triton X-100 and urea, adsorption of impurities on DEAE cellulose, two cycles of electrophoresis in Triton-containing polyacrylamide gels and electrophoresis in SDS-containing gradient gels. Cytochrome b559 becomes labeled with both [3H]leucine and [35S]methionine and accounts for somewhat less than 1% of the total isotopic incorporation into thylakoid protein. The lipoprotein appears to be fully assembled during the time-course of our labeling experiments.

Characterization of undecaprenol kinase from Lactobacillus plantarum

A membrane-bound undecaprenol kinase from Lactobacillus has been identified by observing the ATP-dependent phosphorylation of [14C]undercaprenol. The product of this reaction was shown to be [14C]undecaprenyl monophosphate by comparison of its chromatographic mobilities with authentic undecaprenyl monophosphate. It was shown that 32P from [gamma-32P]ATP was incorporated into undecaprenyl monophosphate. The kinase was partially solubilized by a variety of methods utilizing Triton X-100. Both the membrane-associated and solubilized enzymes required Mg2+, Triton X-100 and dimethylsulfoxide for activity. The enzyme preferentially phosphorylated the C34, C50 AND C 55 polyprenols. Geranylgeraniol (C20) and dolichol (C100), however, were utilized only 6% and 13% as well as undecaprenol, respectively. Despite the 8-fold difference in apparent V values, the apparent Km values for dolichol and undecaprenol were both 14 microM. The apparent Km for the nucleotide cosubstrate, ATP, was 2 mM. No other nucleoside triphosphate could substitute for ATP.

On preparative separation of brain mitochondrial monoamine oxidases

A method was developed for solubilization from bovine brain stem mitochondrial fraction of monoamine oxidases deminating biogenic amines. Preparative separation of the monoamine oxidases, possessing different substrate specificities, was achieved by column chromatography on a biospecific adsorbent AH-Sepharose 4 B. The enzyme preparations thus obtained did not contain any detectable by disc-electrophoresis of isoelectrofocusing in polyacrylamide gels proteins which were devoid of the monoamine oxidase activity.

Polypeptide profiles of chlorophyll . protein complexes and thylakoid membranes of spinach chloroplasts

In addition to the major chlorophyll . protein complexes I and II, two minor chlorophyll proteins have been observed in sodium dodecyl sulfate (SDS))-polyacrylamide gels of spinach chloroplast membranes. These minor pigmented zones appeared to be derived from the light-harvesting chlorophyll a/b . protein and from the reaction centre complex of Photosystem II. Data are presented on the polypeptide profiles of purified digitonin-subschloroplast particles, with special regard to the effect of solubilization temperature and extraction of lipids. The results are compared with the SDS-polypeptide pattern of spinach thylakoids obtained under exactly the same conditions with respect to electrophoresis technique, solubilization method and presence of lipid. In addition, the effects of temperature and lipid extraction on the distinct chlorophyll . protein complexes appearing in SDS gel electrophoretograms of chloroplast membranes were studied by slicing the chlorophyll-containing regions and subjecting them to a second run with or without heating or extraction with acetone. By supplementing these data with an examination of the polypeptide composition of cytochrome f and coupling factor, it has been possible to identify most of the major chloroplast membrane polypeptides.

Some photoreactions of isolated cytochrome b-559

Cytochrome b-559 was isolated from spinach and the alga Bumilleriopsis filiformis (Xanthophyceae) and characterized by functional properties: (a) It was active as electron acceptor in a diaphorase system using NADPH as donor and ferredoxin and ferredoxin-NADP reductase as redox proteins. (b) It exhibited photooxidation with Photosystem-I particles, when illuminated with 707 nm light. (c) It was photooxidized by Photosystem-II particles and 652 nm light at room temperature. Light greater than 702 nm was ineffective. The data corroborate previous reports on redox reactions of bound cytochrome b-559.

Kinetics of the photoreduction of cytochrome b-559 by photosystem II in chloroplasts

The kinetics of the photoreduction of cytochrome b-559 and plastoquinone were measured using well-coupled spinach chloroplasts. High potential (i.e, hydroquinone reducible) cytochrome b-559 was oxidized with low intensity far-red light in the presence of N-methyl phenazonium methosulfate or after preillumination with high intensity light. Using long flashes of red light, the half-reduction time of cytochrome b-559 was found to be 100 +/- 10 ms, compared to 6-10 ms for the photoreduction of the plastoquinone pool. Light saturation of the photoreduction of cytochrome b-559 occurred at a light intensity less than one-third of the intensity necessary for the saturation of ferricyanide reduction under identical illumination conditions. The photoreduction of cytochrome b-559 was accelerated in the presence of dibromothymoquinone with a t 1/2 = 25-35 ms. The addition of uncouplers, which caused stimulatory effect on ferricyanide reduction under the same experimental conditions resulted in a decrease in the rate of cytochrome b-559 reduction. The relatively slow photoreduction rate of cytochrome b-559 compared to the plastoquinone pool implies that electrons can be transferred efficiently from Photosystem II to plastoquinone without the involvement of cytochrome b-559 as an intermediate. These results indicate that it is unlikely that high potential cytochrome b-559 functions as an obligatory redox component in the main electron transport chain joining the two photosystems.

Picosecond laser study of fluorescence lifetimes in spinach chloroplast photosytem I and photosystem II preparations

Fractions enriched in either Photosystem I or Photosystem II have been prepared from chloroplasts with digitonin. A more detailed analysis of the decay kinetics of fluorescence excited by a picosecond laser pulse has been possible compared to experiments with unfractionated systems. The Photosystem I fractions show a very short component (less than or equal to 100 ps) at room temperature which is apparently independent of pulse intensity over the range of photon densities used (5 - 10(13)--1 - 10(16) photons cm-2). The Photosystem II fraction has a short initial lifetime at room temperature which is strongly intensity-dependent approaching 500 ps at low photon densities, but decreasing to close to 150 ps at the highest photon densities. All of these room temperature decays appear to be non-exponential, and may possibly be fitted by at t1/2 expression, expected from a random diffusion of excitations via Förster energy transfer. On cooling to 77K, lifetimes of both Photosystem I and Photosytem II increase, the lengthening with Photosystem I being more striking. The Photosystem I decays become intensity dependent like the Photosystem II, and at the lowest photon densities decays which are more nearly exponential within the experimental error give initial lifetimes of about 2 ns. The non-exponential decays seen at high photon densities appear to fit a t1/2 expression.

Lymphocyte surface immunoglobulins: detection, characterization, and occurrence in disease of the lymphoid system

Surface immunoglobulins (Igs) of lymphocytes are of considerable interest because these molecules probably function as receptors for antigen, and knowledge of their molecular properties should provide information on the mechanisms of immune differentiation. The density and types of surface Ig on a cell provide markers useful in indicating the class of a lymphocyte and its stage of maturity. Moreover, knowledge of the specificities of the surface Ig of neoplastic lymphocytes might suggest the nature of agents involved in the generation of the disease. Two broad classes of lymphocytes, bone marrow-derived lymphocytes (B cells) active in antibody secretion, and thymus-derived lymphocytes (T cells) which mediate cellular immune reactions, and their subpopulations must be considered with reference to the nature, origin, and function of their surface immunoglobulin. This article analyzes direct and indirect methods for the demonstration of surface Igs and describes certain physicochemical properties of isolated surface Ig molecules. Roles of these surface molecules in recognition of antigen, initiation of all differentiation, and cooperation among lymphocytes and accessory cells are discussed.

Effect of the hydrophile-lipophile balance of non-ionic detergents (Triton X-series) on the solubilization of biological membranes and their integral b-type cytochromes

The solubilization of four integral membrane proteins (i.e. cytochrome b-561 of the chromaffin granule membrane, cytochrome b5 of the endoplasmic reticulum and the mitochondrial b-type cytochrome(s) as well as cytochrome c oxidase) has been studied at 0 degrees C using the non-ionic detergents of the Triton X-series having the common hydrophobic 4(1,1,3,3-tetramethylbutyl)phenoxy (t-octyl-phenoxy) group and a variable average number (n) of polar ethylene oxide units added. Following a pre-extraction of peripheral membrane and matrix proteins with low and high salt concentration and a weak non-ionic detergent (Tween 20, average hydrophile-lipophile balance (HLB) = 16.7), the amount of heme proteins solubilized by subsequent Triton X-solutions was measured. With the detergents tested the degree of solubilization decreased in the sequence cytochrome b-561 greater than cytochrome b5 greater than mitochondrial cytochrome(s) b and parallelled the effect of the detergents on light scattering and the phospholipid to protein ratio of the three membranes. For all the b-cytochromes, the solubilizing power of the detergent increased with decreasing average length of the polar ethylene oxide chain and the hydrophile-lipophile balance as long as clouding did not occur (e.g. Triton X-114,n = 7.5 and HLB = 12.4). Thus, the greatest difference in the degree os solubilization of the three cytochromes was observed with Triton X-405 (n = 40 and HLB = 17.9). All the cytochromes were most efficiently solubilized (i.e. approx. 90%) by Triton X-100 (n = 9.5 and HLB = 13.5).

Purification and properties of a periplasmic aminoendopeptidase from Escherichia coli

A periplasmic aminoendopeptidase from Escherichia coli has been purified to hemogeneity. It is a monomer of molecular weight 45000 and containing one -- SH group that is necessary for catalytic activity. The study of its substrate specificity indicated that the enzyme has both aminopeptidase and endopeptidase activity. The pH optimum for L-alanine p-nitroanilide hydrolysis is between 7 and 7.5 and that for 125I-labeled casein proteolysis between 7.3 and 7.6. The activation energy for the hydrolysis of L-anine p-nitroanilide was calculated to be 5.3 kcal X mol-1 (22.2 kJ X mol-1).

Yeast manno-protein biosynthesis: solubilization and selective assay of four mannosyltransferases

Using appropriate yeast strains and exogenous acceptors, we have devised specific assays for four mannosyltransferase activities involved in biosynthesis of the carbohydrate outer chain of yeast mannoproteins. The assays utilize GDP-[14C]mannose as the donor and unlabeled oligosaccharides as the acceptors, the products being neutral radioactive oligosaccharides one mannose unit larger than the acceptors. The multiglycosyltransferase system from Saccharomyces cerevisiae was solubilized in Triton X-100 and urea and purified 100-fold. Free mannose is an acceptor for the alpha1 leads to 2-mannosyltransferase, the major product being alpha[14C]Man leads to 2Man. The alpha1 leads to 6-mannooligosaccharides serve as acceptors for both the alpha1 leads to 2- and alpha1 leads to 6-transferases, but the tetrasaccharide alphaMan leads to 3alphsMan leads to 2alphaMan is a specific acceptor for the latter enzyme and yields (see article). When reduced, this same tetrasaccharide serves as the acceptor for an alpha1 leads to 3-mannosyltransferase from Saccharomyces chevalieri, yielding a pentasaccharide with two terminal 1 leads to 3 linkages. Assay of the alpha1 leads to 3-transferase in S. cerevisiae utilizes reduced alpha1 leads to 2-mannotriose as the acceptor, the product being alpha[14C]Man leads to 3alphaMan leads to 2alphaMan leads to 2Mannitol. The multienzyme system works in concert to make "mannan" in a cell-free in vitro system.

Chloroplast cytochrome b-6. Molecular composition as a lipoprotein

Disc electrophoretically homogeneous spinach-chloroplast cytochrome b-6 was found to be a lipoprotein whose redox potential was essentially unchanged during isolation. These results further support the hypothesis of Triton X-100/4 M urea, pH 8, as a useful extracting medium for membrane lipoproteins. Cytochrome b-6 was found to have a heme equivalent dry weight of 1 mol of heme per 60000 g. Of this, 20000 g was lipid-extractable. The molecular weight was 60000 with a partial specific volume of 0.84 ml/g. The protein portion of the molecule (40000) consisted of 1 polypeptide chain of 20000 daltons, 1 of 9600 daltons and 2 of 6600 daltons. A simple lipid composition (relative to the original membrane) was found consisting of 7 mol of chlorophyll a and 6 mol of cardiolipin per mol of cytochrome; these two lipids thus account for about 75-80% of the lipid content. An unidentified minor neutral lipid and minor polar lipid were also detected. At pH 7.0 in the presence of 0.5% Triton X-100, E'-o was -0.080 V, and in the absence of Triton X-100, E'-o was -0.120 V. At pH 8 in 0.5% Triton X-100, E'-o was -0.084 V, thus indicating that the redox potential is independent of pH in the region 7-8. The redox reaction proceeded via a one-electron-transfer.