Crystallization and preliminary X-ray study of a new crystal form of cytochrome c' from Rhodobacter capsulatus

A new crystal form of diheme cytochrome c' from Rhodobacter capsulatus has been obtained and preliminary crystallographic experiments have been performed. The crystals belong to the space group P2(1)2(1)2 with unit-cell dimensions of a = 47.82, b = 72.59, c = 34.32 A. The assumption that an asymmetric unit of the crystal contains one half of the homodimer molecule indicates that the monomers in the dimeric molecule may be related by a crystallographic twofold axis. Crystals diffract up to 1.7 A resolution using the X-ray beam from synchrotron radiation, and 11 127 unique structure factors were obtained with an R(merge) of 7.1% from 52 922 indexed reflections. Structure analysis by means of molecular-replacement methods is now underway.

Influence of charge and polarity on the redox potentials of high-potential iron-sulfur proteins: evidence for the existence of two groups

We have investigated the HiPIPs from Ectothiorhodospira vacuolata (iso-1 and iso-2), Chromatium vinosum, Rhodocyclus gelatinosus, Rhodocyclus tenuis (strain 2761), Rhodopila globiformis, and Rhodospirillum salinarum (iso-2) by direct electrochemistry. Using a glassy carbon electrode with a negatively charged surface, direct, unpromoted electrochemistry is possible with the positively charged HiPIPs. With the negatively charged HiPIPs, the positively charged and flexible bridging promoter poly(L-lysine) is required. The stability of the response can be improved by morpholin, aspartate, tryptophan, or 4,4'-dipyridyl. These "stabilizers" prevent the blocking of the electrode by denatured protein. The redox potential of 500 mV found for R. salinarum iso-2 is the highest HiPIP potential reported. The presence of histidines in the sequence does not per se predict a pH-dependent redox potential. Only C. vinosum and R. gelatinosus HiPIPs show a weak but significant pH dependence with a difference of 35 mV between the low- and the high-pH form and maximum slopes of -20 mV/unit. The dependence of the midpoint potential on temperature and on ionic strength varies over the different HiPIPs. The dependence of the potentials on square root of I cannot be fully explained by the Debye-Hückel theory because the linearity exceeds the limiting concentration and only small negative slopes are observed (o to -28 mV/square root of M) Combination of the sequences, the optical spectra, the overall charges, and the redox thermodynamics suggests that existence of two groups of HiPIPs. One group consists of Chromatium-like HiPIPs with redox potentials between 300 and 350 mV, modulated only by the solvation of the cluster. The second group is formed by Ectothiorhodospira-like HiPIPS with potentials between 50 and 500 mV, modulated by the overall charge of the peptide (25 mV/unit) and by the solvation of the cluster.

Molecular cloning and sequencing of cytochrome c' from the phototrophic purple sulfur bacterium Chromatium vinosum

The gene for cytochrome c' from Chromatium vinosum was cloned from a HindIII-SalI digest of genomic DNA. A 1.4 kbp fragment containing the gene was sequenced in both directions using the Sanger dideoxy method. The cytochrome c' gene codes for a 154-residue peptide, of which the last 131 amino acids match the previously determined sequence of the protein. The remaining 23 residues represent a signal sequence that is cleaved from the polypeptide upon translocation to the periplasmic space. An additional open reading frame on the other strand of the fragment codes for a peptide that contains four regions that are homologous to corresponding regions of the cytochrome b-type subunit of several Ni-Fe hydrogenases.

Reduced left ventricular systolic pump performance and depressed myocardial contractile function in patients > 65 years of age with normal ejection fraction and a high relative wall thickness

We studied the relation between relative wall thickness, left ventricular systolic pump performance, and myocardial contractile function in 77 older patients with normal ejection fraction who were free of valvular and myocardial ischemic disease. Group 1 comprised 49 patients with relative wall thickness > or = 0.45; group 2 (n = 28) had normal relative wall thickness. Pump performance was characterized by stroke volume index, cardiac index, and stroke work; myocardial function was characterized by midwall shortening and circumferential stress versus shortening relations. Group 1 patients had lower end-diastolic volume (83 +/- 3 vs 124 +/- 5 ml, p < 0.05), cardiac index (2.6 +/- 0.2 vs 3.5 +/- 0.1 L/min/m2, p < 0.05), and stroke work/100 g left ventricular mass (43 +/- 2 vs 53 +/- 3 g-m/100 g, p < 0.005). Although there was no significant difference with regard to ejection fraction or fractional shortening at the endocardium, fractional shortening at the midwall was significantly lower in group 1 than in group 2 (16 +/- 1% vs 19 +/- 1%, p < 0.005). This lower value for midwall shortening was observed despite lower values for endsystolic stress, implying decreased myocardial contractile function. Lower stroke volume index in group 1 patients, likely due to small chamber size, was not offset by increased heart rate, resulting in a low-normal cardiac index; in 33% of group 1 patients, cardiac index was < 2.2 L/min/m2, indicating reduced pump performance. Our data indicate an abnormality in pump performance and myocardial function in patients who have high relative wall thickness and normal ejection fraction.

Exercise capacity and skeletal muscle structure and function before and after balloon mitral valvuloplasty

This study evaluated the effects of balloon mitral valvuloplasty (BMV) on exercise capacity and skeletal muscle structure and function in 10 subjects with mitral stenosis (mean age +/- SD 33 +/- 5.5). Measurements were obtained before, and 2 weeks and 4 months after BMV to provide baseline data, to examine the effects of improved hemodynamics, and to examine the effects of resumption of normal physical activity, respectively. Valvuloplasty caused an increase in mitral valve area (0.89 +/- 0.04 to 1.75 +/- 0.07 cm2; mean +/- SE), and an increase in resting cardiac output (3.8 +/- 0.18 to 4.6 +/- 0.19 L/min, p < 0.05). At early follow-up after 2 weeks, subjects did more work (31% increase, p < 0.01) and had greater maximal oxygen consumption (11% increase, p < 0.01). However, measurements reflecting skeletal muscle histology, biochemistry, and function were unaltered at this stage. Four months after BMV, subjects had a further increase in exercise capacity compared with both baseline (58% increase, p < 0.01) and early follow-up (20% increase, p < 0.05). There were associated late increases compared with baseline in quadriceps cross-sectional area (66 +/- 5.8 vs 61 +/- 5.5 cm2, p < 0.05) and torque production (125 +/- 14 vs 118 +/- 16 Nm, p < 0.05). The percentage of slow twitch type I fibers increased compared with baseline (41 +/- 2.0% vs 33 +/- 3.1%, p < 0.05), as did the size of type II fibers (5.9 +/- 0.49 vs 4.9 +/- 0.57 microns2 x 10(3), p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible super-reduction of the cubane [4Fe-4S](3+;2+;1+) in the high-potential iron-sulfur protein under non-denaturing conditions. EPR spectroscopic and electrochemical studies

The reversible 2 x 1 e- reduction of the cubane cluster from oxidized to reduced to super-reduced states ([4Fe-4S]3+<-->[4Fe-4S]2+<-->[4Fe-4S]1+) was studied in high-potential iron-sulfur proteins (HiPIPs). Super-reduction to the 1+ state was not observed in any of the seven HiPIPs tested during cyclic voltammetry (down to -0.95 V). However, equilibration at low potential (pH 7.5) of Rhodopila globiformis HiPIP yields a transient peak around -0.47 V due to the oxidation of super-reduced HiPIP adsorbed at the electrode. The peak area depends on the equilibration potential according to a one-electron Nernst curve with a half-wave potential at -0.91 V. Reduction of R. globiformis HiPIP with titanium (III)citrate at pH 9.5 is very slow [pseudo-first-order half-life of 23 min with a 100-fold excess Ti(III)] but is reversible, and the EPR spectrum with g values of 2.04 and 1.92 is similar to that of reduced [4Fe-4S]1+ ferredoxins. Chemical or electrochemical reoxidation of the super-reduced form resulted in an EPR spectrum with g parallel = 2.12 and g perpendicular = 2.03, i.e. identical to that of oxidized HiPIP. From the equilibrium concentration of super-reduced HiPIP at a low concentration of Ti(III), a reduction potential of -0.64 V can be estimated. Super-reduction of the large HiPIP (iso-2) from Rhodospirillum salinarum is also possible with Ti(III)(gz = 2.05) but the super-reduced state is unstable. No super-reduction with Ti(III) was observed for the other HiPIPs. The difference between the electrochemically observed reduction potential and oxidation potential is explained by a fast and reversible conformational change upon super-reduction. The rate of super-reduction with Ti(III) is limited by the small amount (0.1%) of HiPIP in the 2+ state with the super-reduced conformation.

Transient kinetics of intracomplex electron transfer in the human cytochrome b5 reductase-cytochrome b5 system: NAD+ modulates protein-protein binding and electron transfer

Transient kinetics of reduction and interprotein electron transfer in the human cytochrome b5 reductase-cytochrome b5 (b5R-b5) system was studied by laser flash photolysis in the presence of 5-deazariboflavin and EDTA at pH 7.0. Flash-induced reduction of the FAD cofactor of b5R by deazariboflavin semiquinone (in the absence of b5) occurred in a rapid second-order reaction (k2 = 3.1 x 10(8) M-1 s-1) and resulted in a neutral (blue) FAD semiquinone. The heme of cytochrome b5 (in the absence of b5R) was also rapidly reduced in this system with k2 = 3.1 x 10(8) M-1 s-1. When the two proteins were mixed at low ionic strength, a strong complex was formed. Although the heme of complexed b5 could be directly reduced by deazariboflavin semiquinone, the second-order rate constant was nearly an order of magnitude smaller than that of free b5 (k2 = 3.4 x 10(7) M-1 s-1). In contrast, access to the FAD of b5R by the external reductant was decreased by considerably more than an order of magnitude (k2 < 1 x 10(7) M-1 s-1). When an excess of b5R was titrated with small increments of b5 and then subjected to laser flash photolysis in the presence of deazariboflavin/EDTA, interprotein electron transfer from the b5R FAD semiquinone to the heme of b5 could be observed. At low ionic strength (I = 16 mM), the reaction showed saturation behavior with respect to the b5 concentration, with a limiting first-order rate constant for interprotein electron transfer k1 = 375 s-1, and a dissociation constant for protein-protein transient complex formation of approximately 1 microM. The observed rate constants for interprotein electron transfer decreased 23-fold when the ionic strength was increased to 1 M, indicating a plus-minus electrostatic interaction between the two proteins. Saturation kinetics were also observed at I = 56, 96, and 120 mM, with limiting first-order rate constants of 195, 155, and 63 s-1, respectively. In the presence of NAD+, the transient protein-protein complex was stabilized by approximately a factor of two, and limiting first-order rate constants of 360 s-1 were obtained at both I = 56 mM and I = 96 mM and 235 s-1 at I = 120 mM. Thus, NAD+ appears to stabilize as well as to optimize the protein-protein complex with respect to electron transfer. Another effect of NAD+ is to appreciably slow autoxidation and disproportionation of the FAD semiquinone.(ABSTRACT TRUNCATED AT 250 WORDS)

Photobleaching of the photoactive yellow protein from Ectothiorhodospira halophila promotes binding to lipid bilayers: evidence from surface plasmon resonance spectroscopy

The photoactive yellow protein (PYP) from the phototrophic bacterium Ectothiorhodospira halophila is a small, soluble protein that undergoes reversible photobleaching upon blue light irradiation and may function to mediate the negative phototactic response. Based on previous studies of the effects of solvent viscosity and of aliphatic alcohols on PYP photokinetics, we proposed that photobleaching is concomitant with a protein conformational change that exposes a hydrophobic region on the protein surface. In the present investigation, we have used surface plasmon resonance (SPR) spectroscopy to characterize the binding of PYP to lipid bilayers deposited on a thin silver film. SPR spectra demonstrate that the net negatively charged PYP molecule can bind in a saturable manner to electrically neutral, net positively, and net negatively charged bilayers. Illumination with either blue or white light of a PYP solution, which is in contact with the bilayer, at concentrations below saturation results in an increase in the extent of binding, consistent with exposure of a high affinity hydrophobic surface in the photobleached state, a property that may contribute to its biological function. A value for the thickness of the bound PYP layer (23 A), obtained from theoretical fits to the SPR spectra, is consistent with the structure of the protein determined by x-ray crystallography and indicates that the molecule binds with its long axis parallel to the membrane surface.

1H and 13C NMR assignments and structural aspects of a ferrocytochrome c-551 from the purple phototrophic bacterium Ectothiorhodospira halophila

Two-dimensional nuclear magnetic resonance was used to assign the 1H and 13C resonances of ferrocytochrome c-551 from Ectothiorhodospira halophila, a halophilic phototrophic purple bacterium. This 78-residue protein belongs to a small subgroup of class I cytochromes c together with the analogous cytochromes c-551 from E. halochloris and E. abdelmalekii. A nearly complete assignment of 13C resonances was obtained at natural abundance using a gradient-enhanced 1H-detected heteronuclear single quantum coherence experiment (HSQC). This was found to be extremely useful for the unambigous assignment of side chain protons. The secondary structure of the protein was determined from analyses of short- and medium-range nuclear Overhauser enhancements (NOE), amide proton exchange and 13C alpha chemical shifts. Three helices could be identified which are well conserved among the class I cytochromes c. There is some evidence for two other regions of less well defined helical structure. From a preliminary analysis of long-range NOE it is shown that in the E. halophila cytochrome c-551 the general cytochrome c fold is well conserved, including the three conserved helices (residues 2-8, 41-50, 63-76), the regions around the heme ligands (Cys14-Ser15-Ser16-Cys17-His18, Met55) and the omega loop (residues 18-28). In addition, three variable segments of the protein are discussed in detail, one of those including a cis-proline, a feature so far unique in the cytochrome c family. Structural alignments of the E. halophila cytochrome c-551 with two other Pseudomonas cytochrome c5 homologs (Azotobacter vinelandii cytochrome c5 and Chlorobium limicola cytochrome c-555) are provided which are based on sequence similarities and secondary structure alignments.

Regional nonischemic performance as assessed by end-systolic measures of shortening and thickening

OBJECTIVES

Nonischemic contractile segmental performance was characterized by the end-systolic pressure-length and pressure-thickness relations during regional ischemia induced by proximal left anterior descending and left circumflex coronary artery occlusions.

BACKGROUND

The increases in shortening and thickening of the nonischemic myocardium during acute ischemia have been attributed to alterations in the regional loading conditions. However, it is uncertain to what extent ischemia affects the contractile performance of the nonischemic zone.

METHODS

Twenty-seven beagle dogs were instrumented with sonomicrometers and micromanometer pressure gauges. End-systolic pressure-length and pressure-thickness relation data were obtained during vena cava balloon inflation. Control data were obtained in both left anterior descending and left circumflex regions. Then, in random order, either the left anterior descending or left circumflex coronary artery was occluded for 90 s, and hemodynamic and nonischemic end-systolic pressure-length and pressure-thickness data were obtained. After a 45-min recovery period, the other artery was occluded, and the same recordings were obtained.

RESULTS

The end-systolic pressure-length relation exhibited variable degrees of rightward and downward shifts and the end-systolic pressure-thickness relation variable degrees of leftward and downward shifts. Left circumflex coronary artery occlusion was associated with a greater downward displacement (decreased slope) of the nonischemic end-systolic pressure-length relation than left anterior descending coronary artery occlusion. The baseline slope was the best predictor of the change in slope of the end-systolic pressure-length and pressure-thickness relations. The left circumflex coronary artery supplied a larger proportion of left ventricular myocardial mass than the left anterior descending coronary artery.

CONCLUSION

Acute ischemia profoundly affects the end-systolic performance of the nonischemic segment. Furthermore, the site, and probably size, of the ischemic zone may be important determinants of nonischemic contractile performance.

A "parallel plate" electrostatic model for bimolecular rate constants applied to electron transfer proteins

A "parallel plate" model describing the electrostatic potential energy of protein-protein interactions is presented that provides an analytical representation of the effect of ionic strength on a biomolecular rate constant. The model takes into account the asymmetric distribution of charge on the surface of the protein and localized charges at the site of electron transfer that are modeled as elements of a parallel plate condenser. Both monopolar and dipolar interactions are included. Examples of simple (monophasic) and complex (biphasic) ionic strength dependencies obtained from experiments with several electron transfer protein systems are presented, all of which can be accommodated by the model. The simple cases do not require the use of both monopolar and dipolar terms (i.e., they can be fit well by either alone). The biphasic dependencies can be fit only by using dipolar and monopolar terms of opposite sign, which is physically unreasonable for the molecules considered. Alternatively, the high ionic strength portion of the complex dependencies can be fit using either the monopolar term alone or the complete equation; this assumes a model in which such behavior is a consequence of electron transfer mechanisms involving changes in orientation or site of reaction as the ionic strength is varied. Based on these analyses, we conclude that the principal applications of the model presented here are to provide information about the structural properties of intermediate electron transfer complexes and to quantify comparisons between related proteins or site-specific mutants. We also conclude that the relative contributions of monopolar and dipolar effects to protein electron transfer kinetics cannot be evaluated from experimental data by present approximations.

The structure of flavocytochrome c sulfide dehydrogenase from a purple phototrophic bacterium

The structure of the heterodimeric flavocytochrome c sulfide dehydrogenase from Chromatium vinosum was determined at a resolution of 2.53 angstroms. It contains a glutathione reductase-like flavin-binding subunit and a diheme cytochrome subunit. The diheme cytochrome folds as two domains, each resembling mitochondrial cytochrome c, and has an unusual interpropionic acid linkage joining the two heme groups in the interior of the subunit. The active site of the flavoprotein subunit contains a catalytically important disulfide bridge located above the pyrimidine portion of the flavin ring. A tryptophan, threonine, or tyrosine side chain may provide a partial conduit for electron transfer to one of the heme groups located 10 angstroms from the flavin.

Measurement and global analysis of the absorbance changes in the photocycle of the photoactive yellow protein from Ectothiorhodospira halophila

The photocycle of the photoactive yellow protein (PYP) from Ectothiorhodospira halophila was examined by time-resolved difference absorption spectroscopy in the wavelength range of 300-600 nm. Both time-gated spectra and single wavelength traces were measured. Global analysis of the data established that in the time domain between 5 ns and 2 s only two intermediates are involved in the room temperature photocycle of PYP, as has been proposed before (Meyer T.E., E. Yakali, M. A. Cusanovich, and G. Tollin. 1987. Biochemistry. 26:418-423; Meyer, T. E., G. Tollin, T. P. Causgrove, P. Cheng, and R. E. Blankenship. 1991. Biophys. J. 59:988-991). The first, red-shifted intermediate decays biexponentially (60% with tau = 0.25 ms and 40% with tau = 1.2 ms) to a blue-shifted intermediate. The last step of the photocycle is the biexponential (93% with tau = 0.15 s and 7% with tau = 2.0 s) recovery to the ground state of the protein. Reconstruction of the absolute spectra of these photointermediates yielded absorbance maxima of about 465 and 355 nm for the red- and blue-shifted intermediate with an epsilon max at about 50% and 40% relative to the epsilon max of the ground state. The quantitative analysis of the photocycle in PYP described here paves the way to a detailed biophysical analysis of the processes occurring in this photoreceptor molecule.

The photoactive yellow protein from Ectothiorhodospira halophila as studied with a highly specific polyclonal antiserum: (intra)cellular localization, regulation of expression, and taxonomic distribution of cross-reacting proteins

A rabbit antiserum was raised against the photoactive yellow protein (PYP) from Ectothiorhodospira halophila and purified by adsorption experiments to obtain a highly specific polyclonal antiserum. This antiserum was used to obtain the following results. (i) In E. halophila, PYP can be isolated from the fraction of soluble proteins. In the intact cell, however, PYP appeared to be associated with (intra)cytoplasmic membranes, as was concluded from analysis of immunogold-labelled thin sections of the organism. (ii) The regulation of expression of PYP was studied by using dot blot assays, Western blotting (immunoblotting), and rocket immunoelectrophoresis. Under all conditions investigated (light color, salt concentration, and growth phase), PYP was expressed constitutively in E. halophila. However, when Rhodospirillum salexigens was grown aerobically, the expression of PYP was suppressed. (iii) A large number of prokaryotic microorganisms contained a single protein, with an apparent size of approximately 15 kDa, that cross-reacted with the antiserum. Among the positively reacting organisms were both phototrophic and chemotrophic, as well as motile and nonmotile, organisms. After separation of cellular proteins into a membrane fraction and soluble proteins, it was established that organisms adapted to growth at higher salt concentrations tended to have the cross-reacting protein in the soluble fraction. In the cases of R. salexigens and Chromatium salexigens, we have shown that the cross-reacting protein involved is strongly homologous to PYP from E. halophila.

Effect of critical coronary stenosis on regional function of a segment remote from the acute ischemic bed

BACKGROUND

Limited information is available about the earliest manifestations of ischemia in an area of myocardium supplied by a critically constricted vessel following abrupt occlusion of another vessel. The aim of this study was to describe quantitatively the mechanical behavior of different non-ischemic zones, with and without critical stenosis of the supplying artery.

METHODS

Regional myocardial function was measured in 14 open-chest anesthetized dogs, with piezoelectric length and thickness crystals placed within the perfusion beds of the proximal left anterior descending and left circumflex arteries. After baseline recordings, the left circumflex artery was critically constricted and the left anterior descending artery was abruptly occluded for 60 s. The same procedure was repeated after 30 min without stenosis of the artery. After 45 min of recovery, the same protocol was repeated for a narrowed left anterior descending artery.

RESULTS

Regional performance was assessed by analyzing the phases of segmental contraction. In the non-ischemic zone, isovolumic shortening and thickening and systolic shortening increased following left anterior descending artery occlusion, whereas, in the presence of critical constriction of the circumflex artery, isovolumic and systolic shortening and thickening did not increase. Occlusion of the left circumflex artery resulted in a significant increase in isovolumic shortening and thickening, ejection shortening, systolic shortening and thickening, whereas, with critical constriction of the left anterior descending artery, the same segment did not exhibit hyperkinesis.

CONCLUSIONS

The compensatory potential of the non-ischemic zone seems to be dependent on whether there is restriction to its vascular supply.

Perindopril and physiologic responses to exercise

Cardiovascular drugs have varying effects on hemodynamic, metabolic, and hormonal responses to exercise. To evaluate the effects of the novel angiotensin-converting enzyme (ACE) inhibitor, perindopril on these exercise-related responses, we studied 9 healthy volunteers in a double-blind, randomized, placebo-controlled trial. After a week of perindopril 4 mg orally daily or placebo therapy, volunteers performed a treadmill effort test; the sequence was repeated after a 1-week washout period. Perindopril caused a significant reduction in mean resting systolic and diastolic blood pressure (SBP, DBP) without increasing resting heart rate (HR); 15-min post-exercise SBP was also significantly reduced. There were no significant differences between the perindopril and placebo effort tests with respect to metabolic indexes studied (serum K+, plasma glucose, plasma free fatty acids) or plasma hormonal concentrations measured (ACTH and cortisol, norepinephrine (NE) and epinephrine (EPI), glucagon and insulin, growth hormone and prolactin, renin activity). In the perindopril arm of the study, however, there were modest but significant increases in mean serum K+ before exercise to immediately after exercise (0.4 +/- 0.1 mM, p < 0.01) and mean plasma glucose from before exercise to 5 min (0.6 +/- 0.2 mM, p < 0.01) and 15 min (0.5 +/- 0.2 mM, p < 0.05) after exercise. These data show that perindopril does not impair the hormonal changes associated with exercise in healthy subjects but induces a more consistent increase in blood K+ and glucose concentrations.

X-Ray structure of the cytochrome c2 isolated from Paracoccus denitrificans refined to 1.7-A resolution

The cytochrome c2 (formerly c550) isolated from Paracoccus denitrificans is one of the larger bacterial c-type proteins examined thus far. The molecular structure of this cytochrome has been redetermined and refined to 1.7-A resolution with a crystallographic R-factor of 17.5% for all measured X-ray data. Like other, smaller c-type cytochromes, the molecule consists of five alpha-helices that wrap around the heme group. In addition, this bacterial cytochrome contains two strands of anti-parallel beta-sheet, five Type I turns, and three Type II turns. The present model differs from the originally determined structure in several regions including the N-terminus, the loop delineated by Asp 25 to Lys 31, the region defined by Trp 86 to Val 88, and the C-terminus. A total of 103 water molecules has been positioned into the electron density map. Six of these waters are directly involved in heme binding.

Serum transferrin receptor in hereditary hemochromatosis and African siderosis

The present investigation evaluated the serum transferrin receptor concentration in subjects with nontransfusional iron overload who were identified in two separate studies on the basis of a serum ferritin level above 400 micrograms/L. Subjects with preclinical hereditary hemochromatosis were evaluated in the first study and those with the African form of iron overload in the second. In the first study, hereditary hemochromatosis was identified in 14 white men on the basis of a persistent elevation in transferrin saturation above 55%. The serum receptor concentration was elevated above the upper cut-off of 8.5 mg/L in two of the subjects, but the mean receptor of 6.1 +/- 1.4 mg/L (mean +/- 2 SE) did not differ significantly from the normal mean for this assay of 5.6 +/- 0.3 mg/L. In the same study, 60 control subjects with secondary iron overload were identified on the basis of a serum ferritin persistently above 400 micrograms/L, with a normal serum C-reactive protein concentration but with a transferrin saturation < 55%. Three of these subjects had an elevated serum receptor concentration but the mean value of 5.5 +/- 0.4 mg/L did not differ from normals nor from subjects with hemochromatosis. In the second study, 49 black Africans with iron overload were divided into those with or without an elevated transferrin saturation. The mean serum receptor concentration of 5.0 +/- 0.8 mg/L and 4.5 +/- 0.4 mg/L, respectively, did not differ statistically. It was concluded that there is no evidence of generalized dysregulation of the transferrin receptor in hemochromatosis or African siderosis.

Molecular structure of the oxidized high-potential iron-sulfur protein isolated from Ectothiorhodospira vacuolata

The high-potential iron-sulfur protein (iso-form II) isolated from Ectothiorhodospira vacuolata has been crystallized and its three-dimensional structure determined by molecular replacement procedures and refined to 1.8-A resolution with a crystallographic R factor of 16.3%. Crystals employed in the investigation belonged to the space group C222(1) with unit cell dimensions of a = 58.4 A, b = 64.7 A, and c = 39.3 A and one molecule per asymmetric unit. Like those HiPIPs structurally characterized thus far, the E. vacuolata molecule contains mostly reverse turns that wrap around the iron-sulfur cluster with cysteine residues 34, 37, 51, and 65 ligating the metal center to the polypeptide chain. There are 57 ordered solvent molecules, most of which lie at the surface of the protein. Two of these water molecules play important structural roles by stabilizing the loops located between Asp 42 and Lys 57. The metal center binding pocket is decidedly hydrophobic with the closest solvent molecule being 6.9 A from S2 of the [4Fe-4S] cluster. The E. vacuolata HiPIP molecules pack in the crystalline lattice as dimers with their iron-sulfur centers approximately 17.5 A apart. On the basis of biochemical properties, it was anticipated that the E. vacuolata HiPIP would be structurally more similar to the HiPIP isolated from Ectothiorhodospira halophila than to the protein obtained from Chromatium vinosum. In fact, the E. vacuolata molecule is as structurally close to the C. vinosum HiPIP as it is to the E. halophila protein due to the presence of various insertions and deletions that disrupt local folding.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein interaction sites obtained via sequence homology. The site of complexation of electron transfer partners of cytochrome c revealed by mapping amino acid substitutions onto three-dimensional protein surfaces

Amino acid substitutions in all but the most divergent of cytochromes c have been categorized as being conservative or radical and mapped onto the three-dimensional structure of yeast cytochrome c. Color-coded, space-filling representations reveal a large 24 A diameter surface area which is invariant or conservatively substituted on the front left face of the cytochrome c molecule. Chemical modifications and mutations which inhibit complex formation and electron transfer with reaction partners also map to this surface. In sharp contrast, the back side of the protein is randomly substituted with both conservative and radical replacements. The invariant/conservatively substituted surface on the front of cytochrome c thus defines the site of interaction with redox partners and provides a measure of its dimensions. Further, this analysis strongly suggests that there is only a single site of oxidation and reduction on cytochrome c for all of its physiological reactions. The same analysis applied to bacterial cytochrome c2 shows that its conserved surface is similar in size and location to that of cytochrome c. Analyses of native and model reaction partners of cytochromes c and c2, such as cytochrome b5, plastocyanin, and bacterial photosynthetic reaction centers, also reveal probable active site surfaces for complexation and electron transfer, which are complementary in size to that of the c-type cytochromes. The availability of a three-dimensional structure and of several closely related amino acid sequences for a given functional class of protein is the only limitation on this type of analysis, which can then serve as a basis for designing site-directed mutagenesis experiments.

Amino acid sequences of cytochromes c2 and c' from the moderately halophilic purple phototrophic bacterium Rhodospirillum salexigens

Rhodospirillum salexigens is a moderately halophilic purple phototrophic bacterium which grows optimally in 8% NaCl. The amino acid sequences of the two principal soluble cytochromes c have been determined. One of these is a cytochrome c2, similar in size to mitochondrial cytochrome c. While clearly of the same sequence class as mitochondrial cytochrome c and the proteins from several other Gram-negative bacteria, it does not show particular affinity to any already known sequence in terms of the percentage sequence identity. The other protein is a cytochrome c', but is also a divergent member of this widespread group. The lack of appreciable sequence identity to other species is probably due to a limit of divergence which has been reached for the majority of purple bacterial species. However, the numbers of insertions and deletions and their locations in cytochromes c2 and c' suggest that R salexigens may be related to Rhodospirillum molischianum. Like other electron transport proteins from halophiles, both of these cytochromes are notable for their high content of arginine as compared with lysine and both are acidic. However, they do not show any particular sequence homology to electron transport proteins that have been characterized from the extremely halophilic phototrophes of the genus Ectothiorhodospira. Thus, it appears that adaptation to halophilic habitats has independently occurred more than once in purple bacteria.

Evolution of photosynthetic reaction centers and light harvesting chlorophyll proteins

It is proposed that there is a single evolutionary origin for photosynthetic reaction centers and also for most light-harvesting chlorophyll proteins. It is generally accepted that the purple bacterial reaction center (quinone-reducing photosystem) and the plant and cyanobacterial PSII (oxygen-evolving photosystem) are homologous. It is also apparent that the green sulfur bacterial reaction center is homologous to cyanobacterial PSI (the pyridine nucleotide reducing photosystem). However, it is less obvious that PSI is related to the purple bacterial reaction center. It is herein proposed that PSI represents a gene fusion of the precursors of small light harvesting bacteriochlorophyll proteins from purple bacteria and purple bacterial reaction centers. Furthermore, it is proposed that reaction centers evolved from the membrane-spanning cytochrome b of the cytochrome bc1 complex and that most membrane-spanning cytochromes may have a common origin.

[During experimental coronary occlusion dobutamine further slows down the time constant of isovolumetric relaxation]

It has been shown that the time constant (tau) of isovolumic left ventricular (LV) pressure fall is shortened by beta-adrenergic stimulation, possibly reflecting enhanced myocardial relaxation and improved uniformity within the LV wall. Conversely, acute regional ischaemia , slows tau due to mechanical nonuniformity between the nonischaemic and the ischaemic regions. In order to assess the effect of inotropic stimulation on LV pressure fall during acute regional ischaemia, 7 anaesthetized dogs (16 +/- 2 kg) were instrumented with LV and aortic micromanometers. Sonomicrometers were implanted in the areas supplied by the left circumflex and anterior descending arteries to monitor subendocardial segment length (L). After baseline recordings, acute regional ischaemia was induced by 60 s occlusion of the proximal circumflex artery. After a 30 min recovery, the same was repeated during dobutamine infusion (5 micrograms/kg/min). In order to derive tau from heart beats with comparable end-systolic pressures, a caval occlusion run was performed at each stage. The % systolic bulging of the ischaemic zone was defined as: (maximal L--end-diastolic L)/end-diastolic L x 100. The fitting of the exponential model used to derive tau was always good (r > or = 0.99). At comparable end-systolic pressures, tau was increased by acute regional ischaemia (36 +/- 2 versus 32 +/- 2 ms, p < 0.01) and reduced by dobutamine infusion (27 +/- 2 versus 32 +/- 2 ms, p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)