Ethanolamine utilization in Salmonella typhimurium: nucleotide sequence, protein expression, and mutational analysis of the cchA cchB eutE eutJ eutG eutH gene cluster.

A fragment of the Salmonella typhimurium ethanolamine utilization operon was cloned and characterized. The 6.3-kb nucleotide sequence encoded six complete open reading frames, termed cchA, cchB, eutE, eutJ, eutG, and eutH. In addition, the nucleotide sequences of two incomplete open reading frames, termed eutX and eutI, were also determined. Comparison of the deduced amino acid sequences and entries in the GenBank database indicated that eutI encodes a phosphate acetyltransferase-like enzyme. The deduced amino acid sequences of the EutE and EutG proteins revealed a significant degree of homology with the Escherichia coli alcohol dehydrogenase AdhE sequence. Mutations in eutE or eutG completely abolished the ability of mutants to utilize ethanolamine as a carbon source and reduced the ability to utilize ethanolamine as a nitrogen source. The product of eutE is most probably an acetaldehyde dehydrogenase catalyzing the conversion of acetaldehyde into acetyl coenzyme A. The product of the eutG gene, an uncommon iron-containing alcohol dehydrogenase, may protect the cell from unconverted acetaldehyde by converting it into an alcohol. The deduced amino acid sequence of cchA resembles that of carboxysome shell proteins from Thiobacillus neapolitanus and Synechococcus sp. as well as that of the PduA product from S. typhimurium. CchA and CchB proteins may be involved in the formation of an intracellular microcompartment responsible for the metabolism of ethanolamine. The hydrophobic protein encoded by the eutH gene possesses some characteristics of bacterial permeases and might therefore be involved in the transport of ethanolamine. Ethanolamine-utilization mutants were slightly attenuated in a mouse model of S. typhimurium infection, indicating that ethanolamine may be an important source of nitrogen and carbon for S. typhimurium in vivo.     

Conserving a volatile metabolite: a role for carboxysome-like organelles in Salmonella enterica

Salmonellae can use ethanolamine (EA) as a sole source of carbon and nitrogen. This ability is encoded by an operon (eut) containing 17 genes, only 6 of which are required under standard conditions (37 degrees C; pH 7.0). Five of the extra genes (eutM, -N, -L, -K, and -G) become necessary under conditions that favor loss of the volatile intermediate, acetaldehyde, which escapes as a gas during growth on EA and is lost at a higher rate from these mutants. The eutM, -N, -L, and -K genes encode homologues of shell proteins of the carboxysome, an organelle shown (in other organisms) to concentrate CO(2). We propose that carboxysome-like organelles help bacteria conserve certain volatile metabolites-CO(2) or acetaldehyde-perhaps by providing a low-pH compartment. The EutG enzyme converts acetaldehyde to ethanol, which may improve carbon retention by forming acetals; alternatively, EutG may recycle NADH within the carboxysome.     

Drug resistance mutations can effect dimer stability of HIV-1 protease at neutral pH.

The monomer-dimer equilibrium for the human immunodeficiency virus type 1 (HIV-1) protease has been investigated under physiological conditions. Dimer dissociation at pH 7.0 was correlated with a loss in beta-sheet structure and a lower degree of ANS binding. An autolysis-resistant mutant, Q7K/L33I/L63I, was used to facilitate sedimentation equilibrium studies at neutral pH where the wild-type enzyme is typically unstable in the absence of bound inhibitor. The dimer dissociation constant (KD) of the triple mutant was 5.8 microM at pH 7.0 and was below the limit of measurement (approximately 100 nM) at pH 4.5. Similar studies using the catalytically inactive D25N mutant yielded a KD value of 1.0 microM at pH 7.0. These values differ significantly from a previously reported value of 23 nM obtained indirectly from inhibitor binding measurements (Darke et al., 1994). We show that the discrepancy may result from the thermodynamic linkage between the monomer-dimer and inhibitor binding equilibria. Under conditions where a significant degree of monomer is present, both substrates and competitive inhibitors will shift the equilibrium toward the dimer, resulting in apparent increases in dimer stability and decreases in ligand binding affinity. Sedimentation equilibrium studies were also carried out on several drug-resistant HIV-1 protease mutants: V82F, V82F/I84V, V82T/I84V, and L90M. All four mutants exhibited reduced dimer stability relative to the autolysis-resistant mutant at pH 7.0. Our results indicate that reductions in drug affinity may be due to the combined effects of mutations on both dimer stability and inhibitor binding.     

Effects of tryptophan and pH on the kinetics of superoxide radical binding to indoleamine 2,3-dioxygenase studied by pulse radiolysis

The reaction of superoxide radical (O2-) with the heme protein indoleamine 2,3-dioxygenase has been investigated by the use of pulse radiolysis. In the absence of the substrate tryptophan (Trp), the ferric enzyme reacted quantitatively with O2- to form the oxygenated enzyme. The rate constant for the reaction (8.0 x 10(6) M-1 s-1 at pH 7.0) increased with a decrease in pH. In the presence of low concentrations of L-Trp (approximately 50 microM), under which the catalytic site of the ferric enzyme is greater than 99% Trp-free at pH 7.0, the only spectral species observed upon O2- binding was L-Trp-bound oxygenated enzyme, the ternary complex. This suggests that under the conditions employed O2- binds first to the ferric enzyme to form the oxygenated enzyme and is followed by rapid binding of L-Trp. It was also found that absorbance changes (delta A) for the enzyme after the pulse were significantly decreased when an increased L-Trp concentration was employed. A 50% decrease in delta A was caused with approximately 50 microM L-Trp at pH 7.0. Similar results were also observed with other indole derivatives with decreasing delta A values in the order of indole, 3-indoleethanol, alpha-methyl-DL-Trp, and D-Trp. These results suggest that there exists a binding site for these compounds in the dioxygenase different from the catalytic site for Trp and, most significantly, that binding of Trp to the effector binding site of the ferric enzyme markedly inhibits its reaction with O2-.     

Covalent incorporation of 3'-O-(4-benzoyl)benzoyl-ATP into a P2 purinoceptor in transformed mouse fibroblasts.

ATP, 3'-O-(4-benzoyl)benzoyl-ATP (BzATP), a photoaffinity analog of ATP, and several other ATP analogs induced an increase in plasma membrane permeability to monovalent ions and normally impermeant metabolites, including nucleotides, in transformed 3T6 mouse fibroblasts. The rank order of agonist potency for induction of nucleotide channels was BzATP (EC50 = 15 microM) greater than ATP (EC50 = 50 microM) approximately adenosine 5'-O-(1-thiotriphosphate) (ATP alpha S) greater than 2-methylthio-ATP (EC50 = 75 microM) approximately 3'-amino-3'-deoxy-ATP greater than adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) (EC50 = 175 microM). Long wavelength UV illumination of 3T6 cells in the presence of greater than or equal to 20 microM BzATP at 4 degrees C, a nonpermeabilizing temperature, followed by removal of unbound BzATP, resulted in the efflux of 86Rb+ and the release of a prelabeled pool of cytoplasmic nucleotides when the temperature was shifted to 37 degrees C. Photoincorporation of BzATP was inhibited by ATP, ATP alpha S, ATP gamma S, and other ATP analogs that induced an increase in plasma membrane permeability to nucleotides in 3T6 cells under nonphotoactivating conditions. GTP, ITP, UTP, adenosine, and ATP analogs that did not alter plasma membrane permeability to nucleotides under nonphotoactivating conditions also had no effect on BzATP photoincorporation. Photoincorporation of BzATP occurred optimally between pH 6.6 and pH 8.2 but was inhibited at pH 6.0. Photoincorporation of BzATP was also modulated by the osmolarity and the divalent cation concentration of the assay medium. The increase in plasma membrane permeability to nucleotides induced by photoincorporated BzATP occurred at the same rate and had the same temperature, pH, ionic strength, and divalent cation requirements as the increase in plasma membrane permeability to nucleotides induced by ATP and BzATP under nonphotoactivating conditions. These findings support the hypothesis that BzATP can be covalently incorporated into a P2 purinoceptor in 3T6 cells that is coupled to plasma membrane channels for ions and other metabolites.     

Effects of bilirubin molecular species on membrane dynamic properties of human erythrocyte membranes: a spin label electron paramagnetic resonance spectroscopy study

Unconjugated bilirubin is a neurotoxic pigment that interacts with membrane lipids. In this study we used electron paramagnetic resonance and the spin labels 5-, 7-, 12-, and 16-doxyl-stearic acid (DSA) to evaluate the depth of the hydrocarbon chain at which interaction of bilirubin preferentially occurs. In addition, we used different pH values to determine the molecular species involved. Resealed right-side-out ghosts were incubated (1-60 min) with bilirubin (3.4-42.8 microM) at pH 7.0, 7.4, and 8.0. Alterations of membrane dynamic properties were maximum after 15 min of incubation with 8.6 microM bilirubin at pH 7.4 and were accompanied by a significant release of phospholipids. Interestingly, concentrations of bilirubin up to 42.8 microM and longer incubations resulted in the elution of cholesterol and further increased that of phospholipids while inducing less structural alterations. Variation of the pH values from 8.0 to 7.4 and 7.0, under conditions of maximum perturbation, led to a change from an increased to a diminished polarity sensed by 5-DSA. Conversely, a progressive enhancement in fluidity was reported by 7-DSA, followed by 12- and 16-DSA. These results indicate that bilirubin while enhancing membrane lipid order at C-5 simultaneously has disordering effects at C-7. Furthermore, recovery of membrane dynamics after 15 min of bilirubin exposure along with the release of lipids is compatible with a membrane adaptive response to the insult. In addition, our data provide evidence that uncharged diacid is the species primarily interacting with the membrane as perturbation is favored by acidosis, a condition frequently associated with hyperbilirubinemia in premature and severely ill infants.     

Role of anionic lipid in bacterial membranes

The major phospholipids of Bacillus stearothermophilus are phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CL). Under the growth conditions used in this study the concentration of anionic lipid (PG + CL) was determined by the pH of the culture medium. Cells grown in a complex medium at pH 5.8, 7.0, and 8.0 contained 17, 29 and 36 nmol of anionic (PG + CL) lipid/mg cell (dry weight). The concentration of the zwitterionic lipid phosphatidylethanolamine (PE) was 17-20 nmol/mg cell (dry weight) under all conditions. Analysis of isolated membrane preparations suggested that the amount of anionic lipid per unit area of membrane increased as the pH of the growth medium was increased. Membranes from cells grown at pH 5.8 and 8.0 contained 130 and 320 nmol anionic lipid/mg membrane protein, respectively. Phosphatidylethanolamine appeared to be localized on the inner membrane surface in cells grown under all conditions. Increasing the ionic strength of the culture medium by the addition of NaCl or KCl had little effect on growth at pH 5.8 but inhibited growth at pH 7 and 8. It was concluded that anionic phospholipid plays an important physiological role in maintaining an acidic pH at the outer membrane surface.     

Redox control in heme proteins: electrostatic substitution in the active site of leghemoglobin

The effects of electrostatic substitutions on the spectroscopic, ligand binding, and redox properties of the heme in leghemoglobin have been examined by replacement of the proximal leucine 88 residue with an aspartic acid residue (Leu88Asp). Electronic and resonance Raman spectra of the ferric derivative of Leu88Asp indicate a mixture of 6-coordinate, high-spin and 6-coordinate, low-spin hemes, analogous to that observed in the recombinant wild-type protein (rLb). At alkaline pH, formation of hydroxide-bound heme is indicated for Leu88Asp; the pK(a) for this transition (8.7 +/- 0.2, micro = 0.10 M, 25.0 degrees C) is 0.4 pH units higher than for rLb. Equilibrium dissociation constants (sodium phosphate, pH 7.0, micro = 0.10 M, 25.0 +/- 0.1 degrees C) for binding of anionic ligands (N(-)(3), nicotinate) to Leu88Asp are higher (K(d,nicotinate) = 6.8 +/- 0.2 microM; K(d,azide) = 33 +/- 0.6 microM) than the corresponding values for rLb (K(d,nicotinate) = 1.4 +/- 0.3 microM (pH 5.5, micro = 0.10 M, 25.0 +/- 0.1 degrees C); K(d,azide) = 4.8 +/- 0.2 microM). Resonance Raman spectra (sodium phosphate, pH 7.0, micro = 0.10 M) for the ferrous derivatives of Leu88Asp and rLb exhibit a strong nu(Fe-His) stretching frequency at 223 cm(-1) in both cases, indicating that the hydrogen bonding structure on the proximal side is not substantially altered in the variant. The reduction potential of Leu88Asp is -14 +/- 2 mV vs standard hydrogen electrode (SHE) (25.0 degrees C, micro = 0.10 M, pH 7.0), a decrease of 35 mV over the corresponding value for the wild-type protein under the same conditions (21 +/- 3 mV vs SHE). An assessment of these data in terms of electrostatic and hydrogen bonding considerations is presented.     

Na+-like effect of imidazole on the phosphorylation of (Na+ + K+)-ATPase

A high basal level of phosphorylation (approx. 70% of the optimal Na+-dependent phosphorylation level) is observed in 50 mM imidazole-HCl (pH 7.0), in the absence of added Na+ and K+ and the presence of 10-100 microM Mg2+. In 50 mM Tris-HCl (pH 7.0) the basal level is only 5%, irrespective of the Mg2+ concentration. Nevertheless, imidazole is a less effective activator of phosphorylation than Na+ (Km imidazole-H+ 5.9 mM, Km Na+ 2 mM under comparable conditions). Imidazole-activated phosphorylation is strongly pH dependent, being optimal at pH less than or equal to 7 and minimal at pH greater than or equal to 8, while Na+-activated phosphorylation is optimal at pH 7.4. This suggests that imidazole-H+ is the activating species. Imidazole facilitates Na+-stimulated phosphorylation. The Km for Na+ decreases from 0.63 mM at 5 mM imidazole-HCl to 0.21 mM at 50 mM imidazole-HCl (pH 7; 0.1 mM Mg2+ in all cases). Imidazole-activated phosphorylation is more sensitive to inhibition by K+ (I50 = 12.5 microM) than Na+-activated phosphorylation (I50 = 180 microM). Mg2+ antagonizes activation by imidazole-H+ and also inhibition by K+. The Ki value for Mg2+ (approx. 0.3 mM) is the same for the two antagonistic effects. Tris buffer (pH 7.0) inhibits imidazole-activated phosphorylation with an I50 value of 30 mM in 50 mM imidazole-HCl (pH 7.0) plus 0.1 mM Mg2+. We conclude that imidazole-H+, but not Tris-H+, can replace Na+ as an activator of ATP-dependent phosphorylation, primarily by shifting the E2----E1 transition to the right, leading to a phosphorylating E1 conformation which is different from that in Tris buffer.     

The base-exchange enzyme activities of sarcolemma and sarcoplasmic reticulum from rat heart

The Ca2+ dependent incorporation of [14C]ethanolamine, L-[14C]serine and [14C]choline into phosphatidylethanolamine, phosphatidylserine and phosphatidylcholine, respectively, were investigated in membrane preparations from rat heart. The ethanolamine and serine base-exchange enzyme-catalyzed reactions were associated with the sarcolemma and sarcoplasmic reticulum. There was a 17.2-fold and 6.8-fold enrichment, respectively, of the serine and the ethanolamine base-exchange enzyme activities in the sarcolemma compared to the starting whole homogenate. The sarcoplasmic reticulum was enriched in the ethanolamine and serine base-exchange enzyme activities. The choline base-exchange enzyme activity of all membranes fractions was negligible compared to the ethanolamine or serine base-exchange enzyme activities. The apparent Km for the ethanolamine and serine base-exchange enzyme in sarcolemma was 14 microM and 25 microM, respectively. The pH optimum for these base-exchange activities was 7.5-8.0. There was a dependence upon Ca2+ for these reactions with a 1 or 4 mM concentration required for maximal activity. The properties of the sarcoplasmic reticulum base-exchange enzymes were similar to the sarcolemmal base-exchange enzymes.     

Sedimentation equilibrium measurements of the intermediate-size tobacco mosaic virus protein polymers

Short-column sedimentation equilibrium methods have been applied for the first time to tobacco mosaic virus (TMV) protein (0.1 M ionic strength orthophosphate) at pH 6.5 and at pH 7.0 to estimate molecular weights. Previous sedimentation velocity experiments at pH 6.5, 20 degrees C have led to the conclusion that the major boundary with an S0(20),w value of 24.4 +/- 0.1 S consists of a distribution of polymers which are mainly three-turn, 48-51-subunit helical rod aggregates. The directly measured z-average molecular weights together with sedimentation velocity data are entirely consistent with this assignment of a three-turn aggregate. Molecular weights have also been determined under two conditions where a large mass fraction of the protein sediments with an S0(20),w value of 20.3 +/- 0.2 S. At pH 6.5, 6-8 degrees C, the aggregates in this boundary are metastable and correspond to 50-60% of the preparation. At pH 7.0, 20 degrees C at equilibrium, 65-75% of the protein sediments at 20.3 S. The 20.3S boundary is very similar under both conditions and is interpreted as being composed of a distribution of protein aggregates centered about 39 +/- 2 subunits. This result is important in the interpretation of previous kinetic measurements of TMV self-assembly. The current view is that the 34-subunit structure of TMV protein, in the form of a cylindrical disk which is made up of two 17-subunit layers and has been characterized in single-crystal X-ray diffraction studies, plays a central role in the initial binding steps with RNA. The present results are not consistent with the view that there is a significant concentration of the TMV protein disk structure in solution under the usual conditions of TMV self-assembly.     

Simultaneous measurements of proton motive force, delta pH, membrane potential, and H+/O ratios in intact Escherichia coli.

An instrument is described that enables the simultaneous monitoring of proton motive force (PMF), membrane potential (delta psi), the delta pH across a membrane, oxidase activity, proton movements, and H+/O ratios. We have studied the relationship existing among these parameters of energy transduction as a critical condition is changed during an experiment. The major findings are: (a) In the pH range of 4.5 to 7.5, increasing the external pH causes an increase in delta psi, internal pH, and oxidase activity, a decrease in H+/O ratio, and a peak-plateau in PMF from pH 5.5 to 6.6 where delta pH is converted to delta psi. (b) An increase in [K+] from 1 to 100 mM, in the presence of 0.5 microM valinomycin, causes the conversion of delta psi to delta pH, a gradual decline in PMF and an increase in H+/O ratio, internal pH, and oxidase activity. (c) Increasing valinomycin concentration from 0 to 2.5 microM, in the presence of 50 mM [K+], causes a decline in delta psi from 125 to 0 mV, and an increase in delta pH from 35 to 70 mV. From 2.5 to 10 microM, the delta pH and the PMF (which it solely represents), stay constant, H+/O ratio increases mainly from 0 to 0.5 microM and much more slowly from 2.5 to 10 microM. (d) Oxygen at only 10% of its concentration in air-saturated buffer can support the generation of 90% or more of the delta psi, delta pH, and PMF generated in an air-saturated solution. (e) The return of extruded protons to the cell (referred to here as "suck-back") represents a complicated process driven by delta psi and influenced by a variety of factors. (f) H+/O ratios measured by the kinetic technique used here are much higher than those measured by standard oxygen pulse techniques.     

Benefits of membrane electrodes in the electrochemistry of metalloproteins: mediated catalysis of Paracoccus pantotrophus cytochrome c peroxidase by horse cytochrome c: a case study

A comparative study of direct and mediated electrochemistry of metalloproteins in bulk and membrane-entrapped solutions is presented. This work reports the first electrochemical study of the electron transfer between a bacterial cytochrome c peroxidase and horse heart cytochrome c. The mediated catalysis of the peroxidase was analysed both using the membrane electrode configuration and with all proteins in solution. An apparent Michaelis constant of 66 +/- 4 and 42 +/- 5 microM was determined at pH 7.0 and 0 M NaCl for membrane and bulk solutions, respectively. The data revealed that maximum activity occurs at 50 mM NaCl, pH 7.0, with intermolecular rate constants of (4.4 +/- 0.5) x 10(6) and (1.0 +/- 0.5) x 10(6) M(-1) s(-1) for membrane-entrapped and bulk solutions, respectively. The influence of parameters such as pH or ionic strength on the mediated catalytic activity was analysed using this approach, drawing attention to the fact that careful analysis of the results is needed to ensure that no artefacts are introduced by the use of the membrane configuration and/or promoters, and therefore the dependence truly reflects the influence of these parameters on the (mediated) catalysis. From the pH dependence, a pK of 7.5 was estimated for the mediated enzymatic catalysis.     

Regulation of cardiac sarcoplasmic reticulum calcium transport by calcium-calmodulin-dependent phosphorylation

Cardiac sarcoplasmic reticulum contains an endogenous calcium-calmodulin-dependent protein kinase and a 22,000-Da substrate, phospholamban. This kinase is half-maximally activated (EC50) by 3.8 +/- 0.3 microM calcium and is absolutely dependent on exogenous calmodulin (EC50 = 49 nM). To determine the effect of this phosphorylation on calcium transport, sarcoplasmic reticulum vesicles (0.5 mg/ml) were preincubated under conditions for optimal phosphorylation (50 mM potassium phosphate, pH 7.0, 10 mM MgCl2, 0.5 mM EGTA, 0.478 mM CACl2, 0.1 microM calmodulin, 0.5 mM ATP). Control sarcoplasmic reticulum was preincubated under identical conditions but in the absence of ATP to avoid phosphorylation. Both control and phosphorylated vesicles were centrifuged and resuspended in 0.3 M sucrose, 20 mM Tris-HCl, 100 mM KCl, pH 7.0, to remove calmodulin and subsequently assayed for calcium (45Ca) transport in the presence of 2.5 mM Tris-oxalate. Phosphorylation of sarcoplasmic reticulum vesicles by calcium-calmodulin-dependent protein kinase resulted in a significant increase (2- to 4-fold) in the rate of calcium transport at low calcium concentrations (less than 3 microM), while calcium transport was minimally affected at higher calcium. Hill coefficients (n) derived from Hill plots of transport data showed no difference between control and phosphorylated sarcoplasmic reticulum (n = 2.0), indicating that phosphorylation does not alter the cooperativity between calcium sites on the calcium pump. The EC50 for calcium activation of calcium transport by control vesicles was 0.86 +/- 0.1 microM calcium, and phosphorylation of phospholamban decreased this value to 0.61 +/- 0.07 microM calcium (n = 7, p less than 0.028), indicating an increase in the apparent affinity for calcium upon phosphorylation. These results were found to be specific for calcium-calmodulin-dependent phosphorylation of phospholamban. Control experiments on the effects of the reactants used in the phosphorylation assay and subsequent centrifugation of sarcoplasmic reticulum showed no alteration of the rate of calcium transport. Therefore, the calcium pump in cardiac sarcoplasmic reticulum appears to be regulated by an endogenous calcium-calmodulin-dependent protein kinase, and this may provide an important regulatory mechanism for the myocardium.     

Unfolding and aggregation during the thermal denaturation of streptokinase.

The thermal denaturation of streptokinase from Streptococcus equisimilis (SK) together with that of a set of fragments encompassing each of its three domains has been investigated using differential scanning calorimetry (DSC). Analysis of the effects of pH, sample concentration and heating rates on the DSC thermograms has allowed us to find conditions where thermal unfolding occurs unequivocally under equilibrium. Under these conditions, pH 7.0 and a sample concentration of less than approximately 1.5 mg x mL(-1), or pH 8.0, the heat capacity curves of intact SK can be quantitatively described by three independent two-state transitions, each of which compares well with the two-state transition observed for the corresponding isolated SK domain. The results indicate that each structural domain of SK behaves as a single cooperative unfolding unit under equilibrium conditions. At pH 7.0 and high sample concentration, or at pH 6.0 at any concentration investigated, the thermal unfolding of domain A was accompanied by the time-dependent formation of aggregates of SK. This produces a severe deformation of the DSC curves, which become concentration dependent and kinetically controlled, and thus precludes their proper analysis by standard deconvolution methods. A simple model involving time-dependent, high-order aggregation may account for the observed effects. Limited-proteolysis experiments suggest that in the aggregates the N-terminal segment 1-63 and the whole of SK domain C are at least partially structured, while domain B is highly unstructured. Unfolding of domain A, under conditions where the N-terminal segment 1-63 has a high propensity for beta sheet structure and a partially formed hydrophobic core, gives rise to rapid aggregation. It is likely that this region is able to act as a nucleus for the aggregation of the full-length protein.     

Retinoid metabolism (LRAT,REH) in the yolk-sac membrane of Japanese quail eggs and effects of mono-ortho-PCBs

Retinoids stored in the avian egg are essential for normal development, however, laboratory and field experiments suggest that they are affected by environmental contaminants. Lecithin:retinol acyltransferase (LRAT) activity was detected in the microsomal fraction of the yolk-sac membrane of the Japanese quail at day 6 of development. LRAT activity was maximal at pH 7.0 having apparent kinetic parameters of K(m)=1.35 microM and V(max)=0.21 nmol/mg protein/h and was inhibited by the sulfhydryl modifying agent N-ethyl-maleimide. Retinol ester hydrolase (REH) activity in the microsomal fraction of the yolk-sac membrane was stimulated by the bile salt analogue 3-[(3-cholamidopropyl) dimethyl-ammonio]-1-propane sulfonate and was maximal at pH 9.0 with apparent K(m)=77 microM and V(max)=34.3 nmol/mg protein/h. Injection of the PCB congener 2,3,3',4,4'-pentachlorobiphenyl increased both REH and LRAT activities, whereas 2,3,3',4-tetrachlorobiphenyl stimulated LRAT. Yolk retinol concentration and the molar ratio retinol:retinyl palmitate were lower in the exposed eggs. Yolk retinol concentration decreased as LRAT increased (R(2)=0.89) suggesting that certain PCB congeners may affect vitamin A mobilization in ovo by increasing LRAT activity in the yolk-sac membrane.     

Iionization of tyrosyl groups of ovalbumin under native and denaturing conditions.

Phenolic titration of ovalbumin was performed in the pH range 7-12 at 30 degrees C and at three ionic strengths viz. 0.033, 0.133 and 0.200. The conformational integrity of ovalbumin was studied by viscosity measurements at different pH values in the pH range 7-12.4. At ionic strength 0.133 two phenolic groups titrated reversibly with pKint = 10.31, and w = 0.032 up to pH 11.25 under native conditions. The value of w expectedly decreased with increase in ionic strength. Two additional phenolic groups became available for reversible titration between pH 11.25 and 11.95 after some conformational change. Above pH 12, the phenolic titration became irreversible and all of the nine tyrosine residues were titrated at pH 13.3 Exposure of ovalbumin to alkaline pH (12.4) caused considerable disruption of the native protein conformation. The reduced viscosity increased from 4.2 ml/g at pH 7.0 to 16.8 ml/g at pH 12.4 under identical conditions of the protein concentration. All of the nine tyrosyl groups of ovalbumin were titrated normally (pKint = 9.9) in a mixture of 5 M guanidine hydrochloride and 1.2 M urea. However, even in this mixture electrostatic interaction, as measured by w was not completely abolished.     

Distribution of mannosamine and mannosaminuronic acid among cell walls of Bacillus species

Some Escherichia coli K-12 lamB mutants, those producing reduced amounts of LamB protein (one-tenth the wild type amount), grow normally on dextrins but transport maltose when present at a concentration of 1 microM at about one-tenth the normal rate. lamB Dex- mutants were found as derivatives of these strains. These Dex- mutants are considerably impaired in the transport of maltose at low concentrations (below 10 microM), and they have a structurally altered LamB protein which is impaired in its interaction with phages lambda and K10 but still interacts with a lambda host range mutant lambda hh*. The Dex- mutants are double lamB mutants carrying one mutation, already present in the parental strains, that reduces LamB synthesis and a second that alters LamB structure. The secondary mutations, present in different independent Dex- mutants, are clustered in the same region of the lamB gene. Dex+ revertants were isolated and analyzed: when the altered LamB protein is made in wild-type amount, due to a reversion of the first mutation, the phenotype reverts to Dex+. However, these Dex+ revertants are still very significantly impaired in maltose transport at low concentrations (below 10 microM).     

Alcohol dehydrogenases in Acinetobacter sp. strain HO1-N: role in hexadecane and hexadecanol metabolism.

Multiple alcohol dehydrogenases (ADH) were demonstrated in Acinetobacter sp. strain HO1-N. ADH-A and ADH-B were distinguished on the basis of electrophoretic mobility, pyridine nucleotide cofactor requirement, and substrate specificity. ADH-A is a soluble, NAD-linked, inducible ethanol dehydrogenase (EDH) exhibiting an apparent Km for ethanol of 512 microM and a Vmax of 138 nmol/min. An ethanol-negative mutant (Eth1) was isolated which contained 6.5% of wild-type EDH activity and was deficient in ADH-A. Eth1 exhibited normal growth on hexadecane and hexadecanol. A second ethanol-negative mutant (Eth3) was acetaldehyde dehydrogenase (ALDH) deficient, having 12.5% of wild-type ALDH activity. Eth3 had threefold-higher EDH activity than the wild-type strain. ALDH is a soluble, NAD-linked, ethanol-inducible enzyme which exhibited an apparent Km for acetaldehyde of 50 microM and a Vmax of 183 nmol/min. Eth3 exhibited normal growth on hexadecane, hexadecanol, and fatty aldehyde. ADH-B is a soluble, constitutive, NADP-linked ADH which was active with medium-chain-length alcohols. Hexadecanol dehydrogenase (HDH), a soluble and membrane-bound, NAD-linked ADH, was induced 5- to 11-fold by growth on hexadecane or hexadecanol. HDH exhibited apparent Kms for hexadecanol of 1.6 and 2.8 microM in crude extracts derived from hexadecane- and hexadecanol-grown cells, respectively. HDH was distinct from ADH-A and ADH-B, since HDH and ADH-A were not coinduced; Eth1 had wild-type levels of HDH; and HDH requires NAD, while ADH-B requires NADP. NAD- and NADP-independent HDH activity was not detected in the soluble or membrane fraction of extracts derived from hexadecane- or hexadecanol-grown cells. NAD-linked HDH appears to possess a functional role in hexadecane and hexadecanol dissimilation.     

Physiological and biochemical role of the butanediol pathway in Aerobacter (Enterobacter) aerogenes.

Aerobacter (Enterobacter) aerogenes wild type and three mutants deficient in the formation of acetoin and 2,3-butanediol were grown in a glucose minimal medium. Culture densities, pH, and diacetyl, acetoin, and 2,3-butanediol levels were recorded. The pH in wild-type cultures dropped from 7.0 to 5.8, remained constant while acetoin and 2,3-butanediol were formed, and increased to pH 6.5 after exhaustion of the carbon source. More 2,3-butanediol than acetoin was formed initially, but after glucose exhaustion reoxidation to acetoin occurred. The three mutants differed from the wild type in yielding acid cultures (pH below 4.5). The wild type and one of the mutants were grown exponentially under aerobic and anaerobic conditions with the pH fixed at 7.0, 5.8, and 5.0, respectively. Growth rates decreased with decreasing pH values. Aerobically, this effect was weak, and the two strains were affected to the same degree. Under anaerobic conditions, the growth rates were markedly inhibited at a low pH, and the mutant was slightly more affected than the wild type. Levels of alcohol dehydrogenase were low under all conditions, indicating that the enzyme plays no role during exponential growth. The levels of diacetyl (acetoin) reductase, lactate dehydrogenase, and phosphotransacetylase were independent of the pH during aerobic growth of the two strains. Under anaerobic conditions, the formation of diacetyl (acetoin) reductase was pH dependent, with much higher levels of the enzyme at pH 5.0 than at pH 7.0. Lactate dehydrogenase and phosphotransacetylase revealed the same pattern of pH-dependent formation in the mutant, but not in the wild type.