Oxidative turnover increases the rate constant and extent of intramolecular electron transfer in the multicopper enzymes, ascorbate oxidase and laccase

Using laser flash photolysis of lumiflavin/EDTA solutions containing ascorbate oxidase, we find that the rate constant for intramolecular electron transfer varies from one enzyme preparation to another and is generally a more sensitive measure of the state of the active site than are steady-state assays. Thus, type I copper is initially reduced in a second-order reaction followed by first-order reoxidation by the type II-III trinuclear copper center. The observed rate constant for this intramolecular process in presumably native enzyme is 160 s-1 at pH 7, whereas an enzyme preparation which had less than 20% activity had a rate constant of 2.6 s-1. Other samples of relatively active enzyme showed biphasic intramolecular kinetics intermediate between the above values. The inactive enzyme sample could be reactivated by dialysis against ascorbate or by treatment with ferricyanide, resulting in a corresponding increase in the intramolecular rate constant for type I copper reoxidation to a value comparable to that of native enzyme. Using this same methodology, we have determined that the type I copper in Japanese lacquer tree laccase is reoxidized by the type II-III trinuclear copper center in a first-order (intramolecular) process with rate constants of 1 s-1 at pH 7.0 and 4.9 s-1 at pH 6.0, values which are approximately two orders of magnitude smaller than for ascorbate oxidase. The intramolecular rate constant and enzyme activity for laccase also increased, but only by a factor of 2-6, when the enzyme was treated with ascorbate or ferricyanide, respectively. We further found that intramolecular electron transfer in laccase was completely inhibited by fluoride ion, in contrast to ascorbate oxidase which is unaffected by this ion. These differences in behavior for these two very similar enzymes are rather remarkable, when it is considered that the distance between copper atoms is constrained by the location of the protein-derived copper ligands in the three-dimensional structure, and that the redox potentials of the enzymes are similar. Our results may be interpreted in terms of an interconversion between active and inactive enzyme in which there is a rearrangement of the type II-III trinuclear copper center, resulting in a lowering of the redox potential and a block in electron transfer. Turnover restores the active enzyme conformation.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of the efficacy of atenolol and its combination with slow-release nifedipine in chronic stable angina

There is still uncertainty of whether combined therapy with a beta-blocker and calcium-channel antagonist provides additive or synergistic clinical benefits in most patients with stable angina pectoris. The comparative antianginal effect of atenolol 50 mg and atenolol 50 mg and slow release nifedipine (20 mg) twice a day was assessed in 27 patients with chronic stable angina in a randomized, double-blind, crossover study. After a 4 week run-in period on atenolol, patients were randomly allocated to receive either atenolol alone or its combination with nifedipine and then crossed over to the alternative treatment for a further 4 weeks. Symptom-limited exercise treadmill tests were performed according to the Naughton protocol. The major endpoints in this study were (a) exercise time to pain; (b) exercise time to > or = 1 mm ST depression; (c) total exercise time; (d) maximal ST-segment depression; (e) number of anginal attacks; and (f) nitrate consumption. The preexercise systolic blood pressure was lower on the combination treatment than on atenolol alone, but heart rate was lower on atenolol compared with the combination treatment. There was no difference in the systolic blood pressure at the onset of pain or at 1 mm ST depression, while heart rate was lower on both occasions with atenolol compared to the combination treatment. There was no difference between the two treatments in terms of the rate-pressure product at the onset of pain or at 1 mm ST depression. Twice as many patients experienced pain later with the combination treatment than with atenolol alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of laser flash photolysis time-resolved spectrophotometry to investigate interprotein and intraprotein electron transfer mechanisms

A description is given of the methodology developed in our laboratory for the application of laser flash photolysis to the elucidation of the kinetics and mechanism of electron transfer processes which occur intermolecularly between two protein molecules within a collisional complex, or intramolecularly between two redox centers within a single multisubunit or multidomain protein. This involves the use of flavin analogs, excited to their lowest triplet state by a laser flash, to initiate electron transfer, either by oxidation of a sacrificial donor followed by redox protein reduction via the flavin semiquinone, or by direct oxidation of a reduced redox protein by the flavin triplet. Time-resolved spectrophotometry is used to follow the course of the sequence of electron transfer events initiated by the laser flash. The application of this methodology to the following systems is described: cytochrome c/cytochrome c peroxidase; ferredoxin/ferredoxin NADP+ reductase; cytochrome c/plastocyanin; flavocytochrome b2; and sulfite oxidase.

Transient proton uptake and release is associated with the photocycle of the photoactive yellow protein from the purple phototrophic bacterium Ectothiorhodospira halophila

Upon excitation by a laser flash at 445 nm, the photoactive yellow protein (PYP) undergoes a bleach and red-shift occurring in less than 10 ns, undergoes a further bleach in approximately 200 microseconds, and then recolors in approximately 200 ms. A conformational change occurs during photobleaching which exposes a hydrophobic site. We have now shown that this photocycle also involves a net uptake of one proton during formation of the fully bleached second intermediate, followed by an equivalent proton release upon return of PYP to the ground state. Proton uptake lags slightly behind PYP bleaching and is first-order, indicating that the protein conformational change occurs in two steps. The results suggest that a basic residue which is normally buried in the protein interior is transiently exposed to solvent during the PYP photocycle and, as a consequence, undergoes a change in pK. On the basis of the crystal structure of PYP, we propose that this basic residue is lysine 111.

Amino acid sequence of a high redox potential ferredoxin (HiPIP) from the purple phototrophic bacterium Rhodopila globiformis, which has the highest known redox potential of its class

Rhodopila globiformis HiPIP has a redox potential (ca. 450 mV) that is 100 mV higher than any other known iron-sulfur protein. The amino acid sequence contains 57 residues and can be aligned with that of Thiobacillus ferrooxidans without any insertions or deletions and is 51% identical. Rp. globiformis HiPIP is also similar to that of Rhodocyclus tenuis, but six- and two-residue gaps must be postulated and there is only 37% identity. Most of the amino acid residues near the iron-sulfur cluster are similar in these two species based on inspection of the three-dimensional structure of Rc. tenuis HiPIP. The reason for the higher redox potential may be a more hydrophilic environment of the Rp. globiformis HiPIP iron-sulfur cluster due to the above two deletions and to substitution of Ser 32 for Gly. Rp. globiformis is unusual in that it has a cytochrome c2 in addition to the HiPIP, and it too has a very high redox potential. These results suggest that the cytochrome c2 and HiPIP may function interchangeably and that the species normally resides in a very high potential environment, although it is not known to grow aerobically in the dark.

Amino acid sequences of cytochromes c-551 from the halophilic purple phototrophic bacteria, Ectothiorhodospira halophila and E. halochloris

The cytochromes c-551 from Ectothiorhodospira halophila and E. halochloris contain 78 and 79 residues, respectively. The sequences can be aligned without the need to postulate any internal deletions or insertions to give 63% identity. They are apparently distantly related to the class I cytochromes c, based on the location of the heme attachment site near the N-terminus and the sixth ligand methionine near the C-terminus. Alignment with cytochromes c5 from Azotobacter and Pseudomonas, with cytochromes c6 from cyanobacteria and algae, and with cytochromes c-555 from the green phototrophic bacteria suggests that residues which occupy important positions in the three-dimensional structures of these proteins have their equivalents in the Ectothiorhodospira cytochromes c-551, but the levels of overall identity are very low, around 30%. Although the Ectothiorhodospira cytochromes c-551 are apparently distantly related to the above, they should be regarded as representative of a new subclass of type I bacterial cytochromes c. Homologs of all of the cytochromes c normally found in Pseudomonas and Azotobacter have now been found in one or more purple bacterial species. Among these, cytochrome c5 homologs are the most widely occurring in purple, green, and cyanobacteria. For the first time, all families of phototrophic bacteria plus Pseudomonas can be related to one another at the molecular level.

Amino acid residues in Anabaena ferredoxin crucial to interaction with ferredoxin-NADP+ reductase: site-directed mutagenesis and laser flash photolysis

Ferredoxin (Fd) functions in photosynthesis to transfer electrons from photosystem I to ferredoxin-NADP+ reductase (FNR). We have made several site-directed mutants of Anabaena 7120 Fd and have used laser flash photolysis to investigate the effects of these mutations on the kinetics of reduction of oxidized Fd by deazariboflavin semiquinone (dRfH.) and the reduction of oxidized Anabaena FNR by reduced Fd. None of the mutations influenced the second-order rate constant for dRfH. reduction by more than a factor of 2, suggesting that the ability of the [2Fe-2S] cluster to participate in electron transfer was not seriously affected. In contrast, a surface charge reversal mutation, E94K, resulted in a 20,000-fold decrease in the second-order rate constant for electron transfer from Fd to FNR, whereas a similar mutation at an adjacent site, E95K, produced little or no change in reaction rate constant compared to wild-type Fd. Such a dramatic difference between contiguous surface mutations suggests a very precise surface complementarity at the protein-protein interface. Mutations introduced at F65 (F65I and F65A) also decreased the rate constant for the Fd/FNR electron transfer reaction by more than 3 orders of magnitude. Spectroscopic and thermodynamic measurements with both the E94 and F65 mutants indicated that the kinetic differences cannot be ascribed to changes in gross conformation, redox potential, or FNR binding constant but rather reflect the protein-protein interactions that control electron transfer. Several mutations at other sites in the vicinity of E94 and F65 (R42, T48, D68, and D69) resulted in little or no perturbation of the Fd/FNR interaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleotide sequence of the heme subunit of flavocytochrome c from the purple phototrophic bacterium, Chromatium vinosum. A 2.6-kilobase pair DNA fragment contains two multiheme cytochromes, a flavoprotein, and a homolog of human ankyrin

The gene for the cytochrome subunit of Chromatium vinosum flavocytochrome c (sulfide dehydrogenase) was cloned from an EcoRI digest of chromosomal DNA. The mature cytochrome subunit contains 175 amino acid residues and two heme binding sites in agreement with the previously reported amino acid sequence. There is also a signal peptide of 25 residues, which apparently directs the protein to the periplasmic space. There are two open reading frames upstream of the heme subunit gene, which encode a tetraheme cytochrome c and a homolog of human ankyrin. The gene for the flavoprotein subunit of flavocytochrome c is in frame 15 nucleotides downstream of the stop codon for the cytochrome gene. Messenger RNA was isolated from malate grown cells. The transcript is approximately 3 kilobases in size and does not hybridize with a probe containing the tetraheme cytochrome gene and part of the ankyrin homolog gene. The heme subunit and flavoprotein subunit genes thus appear to form an operon. The flavoprotein subunit has a 30-residue signal peptide. The clone ends 95 amino acids into the N-terminal sequence of the mature flavoprotein subunit (which should contain about 400 residues). The apparently periplasmic location of flavocytochrome c has important consequences for the presumed function as a sulfide dehydrogenase, because sulfur, which is the product of oxidation, is stored in the cytoplasm. Our results on the location of the enzyme are incompatible with this function.

Primary structure of a photoactive yellow protein from the phototrophic bacterium Ectothiorhodospira halophila, with evidence for the mass and the binding site of the chromophore

The complete amino acid sequence of the 125-residue photoactive yellow protein (PYP) from Ectothiorhodospira halophila has been determined to be MEHVAFGSEDIENTLAKMDDGQLDGLAFGAIQLDGDGNILQYNAAEGDITGRDPKEVIGKNFFKDVAP+ ++ CTDSPEFYGKFKEGVASGNLNTMFEYTFDYQMTPTKVKVHMKKALSGDSYWVFVKRV. This is the first sequence to be reported for this class of proteins. There is no obvious sequence homology to any other protein, although the crystal structure, known at 2.4 A resolution (McRee, D.E., et al., 1989, Proc. Natl. Acad. Sci. USA 86, 6533-6537), indicates a relationship to the similarly sized fatty acid binding protein (FABP), a representative of a family of eukaryotic proteins that bind hydrophobic molecules. The amino acid sequence exhibits no greater similarity between PYP and FABP than for proteins chosen at random (8%). The photoactive yellow protein contains an unidentified chromophore that is bleached by light but recovers within a second. Here we demonstrate that the chromophore is bound covalently to Cys 69 instead of Lys 111 as deduced from the crystal structure analysis. The partially exposed side chains of Tyr 76, 94, and 118, plus Trp 119 appear to be arranged in a cluster and probably become more exposed due to a conformational change of the protein resulting from light-induced chromophore bleaching. The charged residues are not uniformly distributed on the protein surface but are arranged in positive and negative clusters on opposite sides of the protein. The exact chemical nature of the chromophore remains undetermined, but we here propose a possible structure based on precise mass analysis of a chromophore-binding peptide by electrospray ionization mass spectrometry and on the fact that the chromophore can be cleaved off the apoprotein upon reduction with a thiol reagent. The molecular mass of the chromophore, including an SH group, is 147.6 Da (+/- 0.5 Da); the cysteine residue to which it is bound is at sequence position 69.

Purification and properties of an unusual membrane-derived cytochrome b-561 from the purple phototrophic bacterium Rhodobacter capsulatus, which is structurally related to the bacteriochlorophyll-binding protein, LHII beta

An abundant cytochrome b-561 was solubilized from Rhodobacter capsulatus membranes by successive treatments with perchlorate and butanol/water. Neither procedure was effective alone although they could be combined into a single step. Once solubilized, cytochrome b-561 was purified by standard chromatographic procedures used for water-soluble proteins without addition of butanol or detergents. Cytochrome b-561 appears to be highly acidic, it has a size greater than about 1000 kDa as isolated, and the subunit size measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis is less than 8 kDa. The redox potential measured by cyclic voltammetry is -65 mV at pH 7. The N-terminal amino acid sequence is identical to that of the Rb. capsulatus LHII beta light-harvesting bacteriochlorophyll binding protein subunit which has only 48 amino acid residues, and the mass, determined by mass spectroscopy, is identical to that of LHII beta. There is but one heme per two to three peptide chains of 5 kDa, which suggests that the two extraplanar ligands to the heme are on separate subunits. There is strong exciton splitting in the circular dichroism spectrum in the Soret region indicative of heme-heme interaction. The helix content based on far-uv CD is 41%. Together, these properties of cytochrome b-561 are very similar to those of isolated LHII alpha beta bacteriochlorophyll-protein complexes.

Kinetics of photooxidation of soluble cytochromes, HiPIP, and azurin by the photosynthetic reaction center of the purple phototrophic bacterium Rhodopseudomonas viridis

The photosynthetic reaction center of Rhodopseudomonas viridis contains a bound tetraheme cytochrome c subunit which is the primary electron donor to the photooxidized special pair bacteriochlorophyll. We have tested a variety of soluble electron-transfer proteins for their ability to serve as secondary electron donors to the bacteriochlorophyll via the bound cytochrome by measuring the kinetics of reaction center heme reduction following photooxidation by a laser flash, as a function of soluble protein concentration and ionic strength. All of the soluble redox proteins utilized appear to interact with a negatively charged region on the reaction center and to transfer electrons to the 300-mV heme c-556 of the bound cytochrome. Rps. viridis cytochrome c2 was the best electron donor among those proteins tested, with a second-order rate constant extrapolated to infinite ionic strength of 1.2 x 10(6) M-1 s-1, which is two orders of magnitude larger than that of horse cytochrome c. Rps. viridis cytochrome c2 apparently binds to the reaction center at low ionic strength, as evidenced by a nonlinear dependence of kobs on protein concentration. The limiting first-order electron-transfer rate constant at 6 mM ionic strength is approximately 1300 s-1. Horse cytochrome c and the reaction center also form a complex, with a limiting first-order rate constant for electron transfer which is 5 times smaller than for cytochrome c2. Other cytochromes c2 are intermediate in reactivity. More distantly related cytochromes, HiPIP, and azurin are relatively poor electron donors under the conditions of assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient kinetics of electron transfer from a variety of c-type cytochromes to plastocyanin

Plastocyanin (PC) and its physiological reaction partner cytochrome (cyt) f form a complex which is electrostatically stabilized by interactions between complementary localized charges. We have measured the kinetics of intracomplex electron transfer between several reduced cytochromes and PC using laser flash photolysis. With spinach cyt f and spinach PC, we obtain first-order rate constants, kforward = 2780 s-1 and kreverse = 1050 s-1, for the reversible reaction and a complex dissociation constant of about 23 microM at an ionic strength (I) of 5 mM. The observed rate constant increases by a factor of 2 between I = 5 and 40 mM and then decreases monotonically at higher ionic strengths. This indicates that the complex is not completely dissociated until I = 150 mM and that the proteins within the electrostatically most stable complex are not optimally oriented for electron transfer. Similar results were obtained with turnip cyt f and spinach PC, although in this case intracomplex electron transfer is about 4 times as fast. Horse cyt c also forms an electrostatically stabilized complex with PC, and yields a limiting rate constant for intracomplex electron transfer (1750 s-1) and a dissociation constant (10 microM) comparable to those for spinach cyt f. The ionic strength dependence shows that the complex is more readily dissociated (complete at I = 25 mM) than is that of cyt f and that rearrangement is not required for optimal electron transfer. Addition of polylysine results in 10-fold inhibition of the rate of electron transfer. Pseudomonas cyt c-551 is an acidic cytochrome which does not form a complex with PC.(ABSTRACT TRUNCATED AT 250 WORDS)

The promoter of the gene encoding 3',5'-cyclic adenosine monophosphate (cAMP) response element binding protein contains cAMP response elements: evidence for positive autoregulation of gene transcription

The transcriptional transactivational activities of the phosphoprotein cAMP-response element-binding protein (CREB) are activated by the cAMP-dependent protein kinase A signaling pathway. Dimers of CREB bind to the palindromic DNA element 5'-TGACGTCA-3' (or similar motifs) called cAMP-responsive enhancers (CREs) found in the control regions of many genes, and activate transcription in response to phosphorylation of CREB by protein kinase A. Earlier we reported on the cyclical expression of the CREB gene in the Sertoli cells of the rat testis that occurred concomitant with the FSH-induced rise in cellular cAMP levels and suggested that transcription of the CREB gene may be autoregulated by cAMP-dependent transcriptional proteins. We now report the structure of the 5'-flanking sequence of the human CREB gene containing promoter activity. The promoter has a high content of guanosines and cytosines and lacks canonical TATA and CCAAT boxes typically found in the promoters of genes in eukaryotes. Notably, the promoter contains three CREs and transcriptional activities of a promoter-luciferase reporter plasmid transfected to placental JEG-3 cells are increased 3- to 5-fold over basal activities in response to either cAMP or 12-O-tetradecanoyl phorbol-14-acetate, and give 6- to 7-fold responses when both agents are added. The CREs bind recombinant CREB and endogenous CREB or CREB-like proteins contained in placental JEG-3 cells and also confer cAMP-inducible transcriptional activation to a heterologous minimal promoter. Our studies suggest that the expression of the CREB gene is positively autoregulated in trans.

Laser flash photolysis studies of electron transfer to the cytochrome b5-cytochrome c complex

Rate constants for electron transfer in the complex between recombinant rat mitochondrial outer membrane cytochrome b5 or the tryptic fragment of bovine liver cytochrome b5 and horse mitochondrial cytochrome c were measured by laser flash photolysis of 5-deazariboflavin-EDTA solutions. When an excess of cytochrome b5 was titrated with increasing amounts of cytochrome c at low ionic strength and electron transfer was initiated by a laser flash, both proteins were rapidly reduced by deazariboflavin semiquinone. The initial photoreduction was followed by a slower second-order reduction of b5 complexed oxidized cytochrome c by free reduced cytochrome b5. At an 8:1 ratio of cytochromes b5 to c, the pseudo-first-order rate constant for reduction of complexed cytochrome c increased 3-5-fold between ionic strengths of 5 and 40 mM, and then dropped precipitously at higher ionic strengths. The ionic strength dependent increase in rate constant is likely to be due to relief of steric hindrance via rearrangement of cytochrome c in the complex. The reaction rate showed no sign of saturation at any ionic strength, indicating a first-order rate constant greater than 10(4) s-1 within a transient ternary protein complex; i.e., interprotein electron transfer approaches the largest values previously reported for the stable binary protein complex (approximately 4 x 10(5) s-1). Our results emphasize the flexibility of electron-transfer protein complexes, which had previously been modeled in a single conformation with specific salt bridges. It appears that a variety of orientations can exist within such protein-protein complexes and that the population of conformations changes with ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Early and late changes in left ventricular filling after acute myocardial infarction and the effect of infarct size

To characterize the early (1 week) and late (6 weeks) changes in left ventricular (LV) filling pattern associated with acute myocardial infarction (AMI) 45 patients (mean age 65 +/- 2 years) were studied by Doppler echocardiography. Based on clinical criteria, patients were divided into those with large (group L; n = 12) and those with small (group S; n = 33) infarcts and then compared with 16 age-matched control subjects. The following parameters were calculated from the mitral velocity waveform: (1) peak early and peak atrial velocities and their integrals; (2) peak early to atrial velocity ratio and velocity integral ratio; and (3) the pressure half-time of the early wave. One week after AMI, group L showed a decreased atrial and increased early velocity, velocity ratio and integral ratio, whereas the pressure half-time of the early wave was shorter than that in group S and in control subjects. At 6 weeks group L showed a reduction in early velocity, early to atrial velocity ratio and integral ratio, whereas pressure half-time increased. When groups S and L were combined there was a good inverse correlation between pressure half-time and infarct size as measured by peak enzyme release (r = -0.64, p < 0.001). These data suggest that, depending on infarct size, patients exhibit a "restrictive" filling pattern early after the acute event. This is manifested by the greater proportion of filling occurring in early diastole, reflecting an overall increase in chamber stiffness. At 6 weeks, this pattern is less pronounced presumably due to the remodeling process.

Three-dimensional structure of the high-potential iron-sulfur protein isolated from the purple phototrophic bacterium Rhodocyclus tenuis determined and refined at 1.5 A resolution

The molecular structure of the high-potential iron-sulfur protein (HiPIP) isolated from the phototrophic bacterium, Rhodocyclus tenuis, has been solved and refined to a nominal resolution of 1.5 A with a crystallographic R-factor of 17.3% for all measured X-ray data from 30 A to 1.5 A. It is the smallest of the HiPIP structures studied thus far with 62 amino acid residues. Crystals used in the investigation belonged to the space group P2(1) with unit cell dimensions of a = 36.7 A, b = 52.6 A, c = 27.6 A and beta = 90.8 degrees and contained two molecules per asymmetric unit. The structure was solved by a combination of multiple isomorphous replacement with two heavy-atom derivatives, anomalous scattering from the iron-sulfur cluster, symmetry averaging and solvent flattening. The folding motif for this HiPIP is characterized by one small alpha-helix, six Type I turns, an approximate Type II turn and one Type I' turn. As in other HiPIPs, the iron-sulfur cluster is co-ordinated by four cysteinyl ligands and exhibits a cubane-like motif. These cysteinyl ligands are all located in Type I turns. The hydrogen bonding around the metal cluster in the R. tenuis protein is similar to the patterns observed in the Chromatium vinosum and Ectothiorhodospira halophila HiPIPs. Several of the amino acid residues invariant in the previously determined C. vinosum and E. halophila structures are not retained in the R. tenuis molecule. There are 13 solvent molecules structurally conserved between the two R. tenuis HiPIP molecules in the asymmetric unit, some of which are important for stabilizing surface loops. Interestingly, while it is assumed that this HiPIP functions as a monomer in solution, the two molecules in the asymmetric unit pack as a dimer and are related to each other by an approximate twofold rotation axis.

Effects of mild physical activity, atenolol and the combination on ambulatory blood pressure in hypertensive subjects

OBJECTIVE

To evaluate whether beta-blocker treatment could enhance the effect of a mild physical training programme upon blood pressure.

DESIGN AND METHODS

In 12 hypertensive subjects (mean age: 40.3 years) a prospective randomized Latin square-design trial was performed with three treatments: physical training and placebo tablets; atenolol 50 mg once a day and inactivity; and physical training and atenolol 50 mg once a day.

RESULTS

Training significantly increased maximal ventilatory oxygen consumption (VO2MAX), and there was a decrease in ambulatory diastolic blood pressure (DBP) which did not reach statistical significance. Atenolol alone significantly reduced ambulatory systolic blood pressure (SBP) and DBP. Atenolol alone did not reduce VO2MAX. The combination of training and atenolol resulted in an increase in VO2MAX compared with atenolol alone, but no additional significant fall in blood pressure.

CONCLUSIONS

Atenolol did not enhance the effect of physical training upon blood pressure and had little if any effect upon the training-induced increase in exercise tolerance.

[The evaluation of the end-ejection pressure-length relation as an index of regional contractility]

Although end-systolic pressure-length relationship (ESPLR) is now widely used as a regional substitute for the end-systolic pressure-volume relationship, there are some reservations about its use as an index of systolic performance. This study aimed at assessing whether by using end-ejection (zero aortic flow) as a definition of end-systole, ESPLR can be used to characterize myocardial performance independent of load, and if the choice of the region where to implant the sonomicrometers is critical. Ten anaesthetized dogs (16 +/- 2 kg) were instrumented with a left ventricular (LV) pressure micromanometer and an aortic flow probe. Sonomicrometers were implanted in the apical (L1) and the mid-ventricular (L2) regions of the anterior LV wall, and in the basal region of the lateral wall (L3). End-systolic pressure-length relationships were obtained during acute preload reduction induced by the inflation of a vena caval balloon. This evaluation was repeated after increasing end-diastolic pressure to 14-18 mmHg (delta PL), after increasing systolic pressure by 15 (delta P-I) and 25 mmHg (delta P-II) with graded descending aorta occlusion, and during dobutamine infusions at 2.5 (Db 2.5) and 5 micrograms/kg/min (Db5). End-systolic pressure-length relationships (r > 0.97; pressure range: 70-100 mmHg) were characterized by their slopes (Ees), the extrapolated intercept at zero pressure (L0) and the values of segment length at a pressure of 75 (L75) and 100 mmHg (L100). In all the myocardial regions studied by sonomicrometry, the increments in preload and afterload did not significantly shift ESPLR.(ABSTRACT TRUNCATED AT 250 WORDS)

Controlled trial of physical training in chronic heart failure. Exercise performance, hemodynamics, ventilation, and autonomic function

BACKGROUND

Many secondary abnormalities in chronic heart failure (CHF) may reflect physical deconditioning. There has been no prospective, controlled study of the effects of physical training on hemodynamics and autonomic function in CHF.

METHODS AND RESULTS

In a controlled crossover trial of 8 weeks of exercise training, 17 men with stable moderate to severe CHF (age, 61.8 +/- 1.5 years; left ventricular ejection fraction, 19.6 +/- 2.3%), increased exercise tolerance (13.9 +/- 1.0 to 16.5 +/- 1.0 minutes, p less than 0.001), and peak oxygen uptake (13.2 +/- 0.9 to 15.6 +/- 1.0 ml/kg/min, p less than 0.01) significantly compared with controls. Training increased cardiac output at submaximal (5.9-6.7 l/min, p less than 0.05) and peak exercise (6.3-7.1 l/min, p less than 0.05), with a significant reduction in systemic vascular resistance. Training reduced minute ventilation and the slope relating minute ventilation to carbon dioxide production (-10.5%, p less than 0.05). Sympathovagal balance was altered by physical training when assessed by three methods: 1) RR variability (+19.2%, p less than 0.05); 2) autoregressive power spectral analysis of the resting ECG divided into low-frequency (-21.2%, p less than 0.01) and high-frequency (+51.3%, p less than 0.05) components; and 3) whole-body radiolabeled norepinephrine spillover (-16%, p less than 0.05). These measurements all showed a significant shift away from sympathetic toward enhanced vagal activity after training.

CONCLUSIONS

Carefully selected patients with moderate to severe CHF can achieve significant, worthwhile improvements with exercise training. Physical deconditioning may be partly responsible for some of the associated abnormalities and exercise limitation of CHF, including abnormalities in autonomic balance.

Regional interaction and its effect on patterns of myocardial segmental shortening and lengthening during different models of asynchronous contraction in the dog

OBJECTIVE

The aim was to examine the effect of asynchrony and regional myocardial interaction on the pattern of segmental contraction and relaxation.

METHODS

Three models of asynchrony were produced. Firstly the left anterior descending artery was abruptly occluded for 60 s. Secondly, the same artery was gradually occluded to produce four degrees of ischaemia based on the severity of the mechanical dysfunction. Finally, asynchrony was created by infusing isoprenaline (0.04 microgram.ml-1) into the left circumflex artery. Twelve anaesthetised beagles, weighing 16-21 kg, were used for the study.

RESULTS

The patterns of contraction and relaxation were characterised by analysing the phases of shortening and lengthening, the peak lengthening rate (dL/dt), and the timing from the onset of systole to minimum systolic length. A consistent pattern of shortening and lengthening was evident during all three models of asynchrony. There were reciprocal relations between the extent of isovolumetric shortening in the normal segment and in the abnormal segment, and on occasion between the extent of isovolumetric shortening in the normal segment and the extent of isovolumetric lengthening in the same segment. Normal segments that showed minimal shortening or even some lengthening during isovolumetric systole tended to shorten beyond ejection, while segments that shortened significantly during isovolumetric contraction, lengthened earlier. Despite no change in isovolumetric shortening, segments also shortened after ejection when the opposite segment lengthened in late systole and early diastole.

CONCLUSIONS

The pattern of shortening and lengthening depends on the path of contraction or on its entire loading pattern throughout systole. It is also possible that during early isovolumetric systole a segment can either be unloaded or preloaded by an opposing segment.

Isolation, characterization, and amino acid sequences of auracyanins, blue copper proteins from the green photosynthetic bacterium Chloroflexus aurantiacus

Three small blue copper proteins designated auracyanin A, auracyanin B-1, and auracyanin B-2 have been isolated from the thermophilic green gliding photosynthetic bacterium Chloroflexus aurantiacus. All three auracyanins are peripheral membrane proteins. Auracyanin A was described previously (Trost, J. T., McManus, J. D., Freeman, J. C., Ramakrishna, B. L., and Blankenship, R. E. (1988) Biochemistry 27, 7858-7863) and is not glycosylated. The two B forms are glycoproteins and have almost identical properties to each other, but are distinct from the A form. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis apparent monomer molecular masses are 14 (A), 18 (B-2), and 22 (B-1) kDa. The amino acid sequences of the B forms are presented. All three proteins have similar absorbance, circular dichroism, and resonance Raman spectra, but the electron spin resonance signals are quite different. Laser flash photolysis kinetic analysis of the reactions of the three forms of auracyanin with lumiflavin and flavin mononucleotide semiquinones indicates that the site of electron transfer is negatively charged and has an accessibility similar to that found in other blue copper proteins. Copper analysis indicates that all three proteins contain 1 mol of copper per mol of protein. All three auracyanins exhibit a midpoint redox potential of +240 mV. Light-induced absorbance changes and electron spin resonance signals suggest that auracyanin A may play a role in photosynthetic electron transfer. Kinetic data indicate that all three proteins can donate electrons to cytochrome c-554, the electron donor to the photosynthetic reaction center.

Baroreflex control of stroke volume in man: an effect mediated by the vagus

1. Beat-by-beat changes in cardiac performance in response to arterial baroreceptor stimulation induced by phenylephrine were evaluated by pulsed-wave aortic Doppler ultrasound in eighteen subjects. Stroke distance was used as an index of stroke volume and minute distance as an index of cardiac output; peak velocity was also measured. 2. The sensitivity of the baroreceptor-cardiac reflex was assessed by calculating the slope of the regression lines relating the changes in heart period (R-R interval), peak velocity and stroke distance in response to the rise in systolic blood pressure (SBP) induced by phenylephrine. In ten subjects the experiment was repeated after vagal blockade by atropine. Since the tachycardia induced by vagal blockade could alter the sensitivity of the baroreflex, we compared the results obtained after atropine with those obtained during pacing at similar rates in six subjects with cardiac pacemakers. 3. As R-R interval lengthened in response to the rise in SBP, stroke distance and peak velocity fell sharply. The subjects with a highly sensitive baroreceptor-heart rate reflex showed the greatest fall in peak velocity and stroke distance. The slope of the relationship between R-R interval and SBP for each subject correlated closely with that of peak velocity/SBP (correlation coefficient, r = 0.88) and stroke distance/SBP (r = 0.93) relationships. 4. Atropine virtually abolished all the cardiac reflex changes, despite a considerable increase in SBP induced by phenylephrine. At comparable heart rates achieved by pacing the sensitivity of the baroreceptor-cardiac reflex (calculated from the slopes of the regression lines relating changes in stroke distance and in peak velocity to the rise in SBP) was maintained and was significantly greater when compared to that obtained after vagal blockade. 5. These results show that the stimulation of arterial baroreceptors is accompanied by a fall in the Doppler-derived indices of stroke volume and cardiac output. This response is neural and is abolished by atropine, which indicates that it is mediated through the efferent vagus.