The nature of the primary photochemical events in rhodopsin and isorhodopsin

The nature of the primary photochemical events in rhodopsin and isorhodopsin is studied by using low temperature actinometry, low temperature absorption spectroscopy, and intermediate neglect of differential overlap including partial single and double configuration interaction (INDO-PSDCI) molecular orbital theory. The principal goal is a better understanding of how the protein binding site influences the energetic, photochemical, and spectroscopic properties of the bound chromophore. Absolute quantum yields for the isorhodopsin (I) to bathorhodopsin (B) phototransformation are assigned at 77 K by using the rhodopsin (R) to bathorhodopsin phototransformation as an internal standard (phi R----B = 0.67). In contrast to rhodopsin photochemistry, isorhodopsin displays a wavelength dependent quantum yield for photochemical generation of bathorhodopsin at 77 K. Measurements at seven wavelengths yielded values ranging from a low of 0.089 +/- 0.021 at 565 nm to a high of 0.168 +/- 0.012 at 440 nm. An analysis of these data based on a variety of kinetic models suggests that the I----B phototransformation encounters a small activation barrier (approximately 0.2 kcal mol-1) associated with the 9-cis----9-trans excited-state torsional-potential surface. The 9-cis retinal chromophore in solution (EPA, 77 K) has the smallest oscillator strength relative to the other isomers: 1.17 (all-trans), 0.98 (9-cis), 1.04 (11-cis), and 1.06 (13-cis). The effect of conformation is quite different for the opsin-bound chromophores. The oscillator strength of the lambda max absorption band of I is observed to be anomalously large (1.11) relative to the lambda max absorption bands of R (0.98) and B (1.07). The wavelength-dependent photoisomerization quantum yields and the anomalous oscillator strength associated with isorhodopsin provide important information on the nature of the opsin binding site. Various models of the binding site were tested by using INDO-PSDCI molecular orbital theory to predict the oscillator strengths of R, B, and I and to calculate the barriers and energy storage associated with the photochemistry of R and I for each model. Our experimental and theoretical investigation leads to the following conclusions: (a) The counterion (abbreviated as CTN) is not intimately associated with the imine proton in R, B, or I. The counterion lies underneath the plane of the chromophore in R and I, and the primary chromophore-counterion electrostatic interactions involve C15-CTN and C13-CTN. These interactions are responsible for the anomalous oscillator strength of I relative to R and B. (b) The presence of a small activation barrier (~0.2 kcal mol-1) in the 9-cis - 9-trans excited-state surface is associated with the location of the counterion as well as the intrinsic photophysical properties of the 9-cis chromophore. The principal difference between the 1 1-cis -c 1 -transphoto reaction surface and the 9-cis - 9-trans photoreaction surface is the lack of effective electrostatic stabilization of distorted 9 = 10 conformations due to incomplete charge polarization. (c) Hydrogen bonding to the imine proton, ifpresent, does not involve the counterion. We conclude that water in the active site, or secondary interactions with the protein (not involving the CTN), are responsible. (d) All photochemical transformations involve one-bond photoisomerizations.This prediction is based on the observation of a very small excited state barrier for the I -- B photoreaction and a negative barrier for the R - B phototransformation, coupled with the theoretical prediction that all two-bond photoisomerizations have significant S, barriers while one-bond photoisomerizations have small to negative S, barriers.(e) Rhodopsin is energetically stabilized relative to isorhodopsin due to both electrostatic interactions and conformational distortion, both favoring stabilization of R. The INDO-PSDCI calculations suggest that rhodopsin chromophore-CTN electrostatic interactions provide an enhanced stabilization of -2 kcal mol-1 relative to I. Conformational distortion of the 9-cis chromophore-lysine system accounts for -3 kcal mol-1. (f) Energy storage in bathorhodopsin is-60% conformational distortion and 40% charge separation. Our model predicts that the majority of the chromophore protein conformational distortion energy involves interaction of the C,3(-CH3)=CI4--C,5=N-lysine moiety with nearby (unknown) protein residues. (g) Strong interactions between the counterion and the chromophore in R and I will generate weak, but potentially observable charge-transfer bands in the near infrared. The key predictions are the presence of an observable charge-transfer transition at 859 nm (1 1,640 cm- 1) in I and an analogous, but slightly weaker band at 897 nm (11,150 cm-1) in R. Both transitions involve the transfer of an electron from the counterion into low-lying l theta* molecular orbitals.

Energy storage in the primary photochemical events of rhodopsin and isorhodopsin

The energetics associated with the photoequilibrium (Formula: see text) are measured at 77 K by using pulsed-laser photocalorimetry and a range of excitation wavelengths and relative starting concentrations. Enthalpies for the photochemical transformations R hv----B and I hv----B are measured to be delta HRB = 32.2 +/- 0.9 kcal mol-1 and delta HIB = 27.1 +/- 3.2 kcal mol-1, respectively. Although the value of delta HRB is slightly lower than that reported previously by Cooper of 34.7 +/- 2.2 kcal mol-1 [Cooper, A. (1979) Nature (London) 282, 531-533], the two values are in agreement within experimental error. The energy difference delta HRB - delta HIB = 5.1 +/- 3.3 kcal mol-1 is identical within experimental error with the difference in enthalpies of isorhodopsin and rhodopsin [5.2 +/- 2.3; Cooper, A. (1979) FEBS Lett. 100, 382-384]. We suggest that this result is consistent with the theory that bathorhodopsin is a single, common photochemical intermediate connecting rhodopsin and isorhodopsin.

Time-resolved optical spectroscopy and structural dynamics following photodissociation of carbonmonoxyhemoglobin

A summary is presented of our current understanding of the kinetics of ligand rebinding and conformational changes at room temperature following photodissociation of the carbon monoxide complex of hemoglobin with pulsed lasers. The events which occur subsequent to excitation have been followed over 12 decades in time, from about 100 fs to the completion of ligand rebinding at about 100 ms. Experiments with picosecond and subpicosecond lasers by others, together with molecular dynamics simulations, indicate that by 1 ns the deoxyhemoglobin photoproduct is in a thermally equilibrated ground electronic state, so that subsequent processes are unaffected by the initial laser excitation. The principal results have been obtained from time-resolved optical absorption spectroscopy using a sensitive nanosecond laser spectrometer. Five relaxations have been observed which are interpreted as geminate rebinding at about 50 ns that competes with motion of the ligand away from the heme which produces a tertiary conformational change, a second tertiary conformational change at 0.5-1 microseconds, transition from the R to T quaternary structure at about 20 microseconds, and overall bimolecular rebinding of ligands from the solvent to the R and T quaternary structures at about 200 microseconds and 10 ms. Assuming that the dissociation pathway in photolysis experiments is the reverse of the association pathway, we find that for the R state there is a 40% probability that the ligand will bind to the heme after entering the protein, and a 60% probability that it will return to the solvent. Studies on the alpha-subunit of an iron-cobalt hybrid hemoglobin indicate that carbon monoxide enters the protein at the same rate for both R and T quaternary structures. For the alpha-subunit in the T state the probability of binding after entry is much lower, and the ligand returns to the solvent more than 99% of the time, accounting for the 60-fold overall lower association rate. This decreased probability of binding results from a decreased rate of binding to the heme from within the protein, and not an increased rate of return to the solvent. There are still unresolved problems on the basic structural description of carbon monoxide binding and dissociation, particularly the functional significance of the tertiary relations in both the R and T states, and the precise number of kinetic barriers within the protein.

The effect of quaternary structure on the kinetics of conformational changes and nanosecond geminate rebinding of carbon monoxide to hemoglobin

To determine the effect of quaternary structure on the individual kinetic steps in the binding of carbon monoxide to the alpha subunit of hemoglobin, time-resolved absorption spectra were measured after photodissociation of carbon monoxide from a hemoglobin tetramer in which cobalt was substituted for iron in the beta subunits. Cobalt porphyrins do not bind carbon monoxide. Spectra were measured in the Soret region at room temperature after time delays that varied from a few nanoseconds to the completion of ligand rebinding at about 100 ms. The results show that the liganded molecule, alpha(Fe-CO)2 beta(Co)2, is in the R state, but can be almost completely switched into the T state by the allosteric effectors inositol hexaphosphate and bezafibrate. The geminate yield, which is the probability that the ligand rebinds to the heme from within the protein, is found to be 40% for the R state and less than 1% for the T state. According to the simplest kinetic model, these results indicate that carbon monoxide enters the protein in the R and T quaternary conformations at the same rate, and that the 60-fold decrease in the overall binding rate, of carbon monoxide to the alpha subunit in the T state compared to the R state is almost completely accounted for by the decreased probability of binding after the ligand has entered the protein. The results further suggest that the low probability for the T state results from a decreased binding rate to the heme and not from an increased rate of return of the ligand to the solvent.

A clinical trial of minocycline in lepromatous leprosy

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Dynamics of the quaternary conformational change in trout hemoglobin

The kinetics of conformational changes in trout hemoglobin I have been characterized over the temperature range 2-65 degrees C from time-resolved absorption spectra measured following photodissociation of the carbon monoxide complex. Changes in the spectra of the deoxyheme photoproduct were used to monitor changes in the protein conformation. Although the deoxyheme spectral changes are only about 8% of the total spectral change due to ligand rebinding, a combination of high-precision measurements and singular value decomposition of the data permits a detailed analysis of both their amplitudes and relaxation rates. Systematic variation of the degree of photolysis was used to alter the distribution of liganded tetramers, permitting the assignment of the spectral relaxation at 20 microseconds to the R----T quaternary conformational change of the zero-liganded and singly liganded molecules and spectral relaxations at about 50 ns and 2 microseconds to tertiary conformational changes within the R structure. Analysis of the effect of photoselection by the linearly polarized excitation pulse indicates that a major contribution to the apparent geminate rebinding in the 50-ns relaxation arises from rotational diffusion of molecules containing unphotolyzed heme-CO complexes. The activation enthalpy and activation entropy for the R0----T0 transition are +7.4 kcal/mol and -12 cal mol-1 K-1. Using the equilibrium data, delta H = +29.4 kcal/mol and delta S = +84.4 cal mol-1 K-1 [Barisas, B. G., & Gill, S. J. (1979) Biophys. Chem. 9, 235-244], the activation parameters for the T0----R0 transition are calculated to be delta H = +37 kcal/mol and delta S = +73 cal mol-1 K-1. The similarity of the equilibrium and activation parameters for the T0----R0 transition indicates that the transition state is much more R-like than T-like. This result suggests that in the path from T0 to R0 the subunits have already almost completely rearranged into the R configuration when the transition state is reached, while in the path from R0 to T0 the subunits remain in a configuration close to R in the transition state. The finding of an R-like transition state explains why the binding of ligands causes much smaller changes in the R----T rates than in the T----R rates.

Activities of various macrolide antibiotics against Mycobacterium leprae infection in mice

We evaluated the activities of several macrolide antibiotics against M. leprae infections in mouse footpads. Erythromycin and azithromycin were inactive, while both roxithromycin and clarithromycin were found to be consistently active and, in fact, bactericidal. By both methods, clarithromycin was found to be superior to roxithromycin, a finding which, at least in part, may be a consequence of the higher levels of clarithromycin at the site of infection.

Vaccination with pure Mycobacterium leprae proteins inhibits M. leprae multiplication in mouse footpads

In this study, we evaluated vaccination with a number of purified, as well as recombinant, Mycobacterium leprae proteins for protective efficacy in mice. BALB/c mice were immunized intradermally with various native somatic (purified) or recombinant M. leprae proteins and their synthetic polypeptides emulsified in Freund's incomplete adjuvant. The protective efficacy of these preparations was assessed by enumeration of bacilli in the footpads of mice challenged with viable M. leprae 1 to 2 months following immunization. Protection was afforded by the purified and recombinant 10-kDa M. leprae cytoplasmic heat shock protein, the recombinant cell wall-associated 65-kDa M. leprae heat shock protein, and to a lesser extent, the purified 28-kDa M. leprae cytoplasmic protein (superoxide dismutase). Vaccination with either the purified or recombinant 35-kDa M. leprae cell membrane protein, the synthetic 27-amino-acid N-terminal peptide of the 10-kDa protein, the recombinant 18-kDa M. leprae protein, or the purified 22-kDa cell membrane protein was ineffective. When the interval between immunization and challenge was increased to 6 months, the purified 10-kDa M. leprae protein and the recombinant 65-kDa M. leprae protein lost vaccine efficacy, while a sodium dodecyl sulfate-soluble protein fraction of the M. leprae cell wall (soluble proteins), as had been found previously, continued to protect, suggesting that multiple M. leprae protein epitopes are critical for solid vaccine protection.

Viability of Mycobacterium leprae after multiplication in mice

To measure the rate at which Mycobacterium leprae are killed in the course of the mouse footpad infection after the maximum of multiplication has been achieved, M. leprae were harvested shortly before and at intervals after multiplication had reached the level of 10(6) organisms per footpad, serially diluted, and inoculated into the footpads of passage mice. Beginning 1 year later, foot-by-foot harvests of M. leprae were performed from passage mice, and the proportion of viable organisms in the passage inocula was calculated by means of a most-probable-number calculation. In addition, the proportion of solidly staining M. leprae was measured in the passage inocula. The proportion of viable M. leprae in the passage inocula was found to decrease with the time after multiplication to 10(6) organisms per footpad of donor mice; the half-time of loss of viable M. leprae was 25 days. The proportion of solidly staining organisms appeared to be directly related to the proportion of viable organisms, as measured by mouse passage, and inversely proportional to the time after multiplication to 10(6) organisms per footpad.

Effect of low-level and intermittent minocycline therapy on the growth of Mycobacterium leprae in mice

We evaluated the minimal concentrations of minocycline in the diet and in serum required to inhibit the growth of seven Mycobacterium leprae isolates in mice. Minocycline concentrations of 0.01 and 0.04% in the diet, which resulted in levels in serum of less than or equal to 0.17 and 0.51 microgram/ml, respectively, were consistently and completely inhibitory. Even 0.004% dietary minocycline (levels in serum, less than or equal to 0.08 microgram/ml) partially inhibited five of these strains, while 0.001% minocycline was consistently inactive. For five of these isolates, minocycline at a concentration of 0.04% in the diet given 3 days (Monday, Wednesday, Friday) and 1 day weekly completely inhibited the growth of M. leprae, and minocycline given even 1 day monthly was partially inhibitory for three of these five M. leprae isolates.

Recent Advances in the Genetic Pathogenesis, Diagnosis, and Management of Esophageal Atresia and Tracheoesophageal Fistula: A Review

Infants born with esophageal atresia and tracheoesophageal fistula, a complex congenital malformation occurring in 1/2500-4000 live births, may suffer threats to their cardiac, respiratory, and digestive health in addition to anomalies that may exist in the genitourinary and musculoskeletal systems. Optimal care for these patients throughout their lives is best achieved through a coordinated, multidisciplinary approach that our health care system is not always well-equipped to provide. This review, though not exhaustive, highlights the components of care that pertain to initial surgical reconstruction and subsequent diagnosis and management of the complications that are most frequently encountered. Authors from among the many specialties involved in the care of these patients summarize the current best practice with attention to the most recent advances. Assessment and improvement of quality of life and transition to adult specialists as children grow to adulthood is also reviewed.

Effective vaccination of mice against Mycobacterium leprae with density-gradient subfractions of soluble M. leprae proteins: clues to effective protein epitopes

It had previously been discovered that intradermal mouse vaccination with a protein fraction of Mycobacterium leprae (called soluble proteins) in Freund's incomplete adjuvant (FIA) resulted in consistent and long-lived protection against M. leprae multiplication from subsequent viable footpad challenges. In this study certain density-gradient subfractions of this soluble protein, but not others, in FIA afforded vaccine protection. The results of this study suggest which M. leprae proteins may be involved in protective immunity, particularly 1-3 kD, 10 kD, 65 kD, and those of higher molecular weight.

Efficacy of minocycline in single dose and at 100 mg twice daily for lepromatous leprosy

A clinical trial of minocycline in a total of 10 patients with previously untreated lepromatous leprosy was conducted in order to evaluate the efficacy of a single, initial, 200-mg dose and 100 mg twice daily of minocycline for a total duration of up to 3 months. Patients improved remarkably quickly. Although single-dose therapy did not result in a significant killing of Mycobacterium leprae, viable M. leprae were cleared from the dermis regularly by 3 months of twice-daily therapy, a rate similar to that achieved by minocycline 100 mg once daily. Because more side effects were noted herein than previously with 100 mg daily, we recommend that minocycline, when applied, be administered at 100 mg daily to leprosy patients.

Activity of combinations of dapsone, rifampin, minocycline, clarithromycin, and sparfloxacin against M. leprae-infected mice

In these studies we evaluated the activity of low levels of five antimicrobials against Mycobacterium leprae-infected mice when administered singly and in all possible two- and three-drug combinations. Antibiotics studied were: dapsone (D) 0.0001% in the diet, rifampin (R) 20 mg/kg by gavage once monthly, minocycline (M) 0.004% in the diet, clarithromycin (C) 0.001% in the diet, and sparfloxacin (S) 5 mg/kg by gavage five times weekly. Singly each agent was found bacteriostatic (D + R) or partially bactericidal (M, C, and S) but not fully bactericidal. All 10 two-drug regimens were found at least bacteriostatic, 2 being "partially bactericidal" and 4 being "fully bactericidal." Of the 10 three-drug regimens, 9 were found "fully bactericidal" and the other "partially bactericidal." We conclude that combinations of antibiotics active against M. leprae are generally additive in combination.

Primary dapsone-resistant Hansen's disease in California. Experience with over 100 Mycobacterium leprae isolates

We found that in the years 1978 through 1981 only one of 54 previously untreated patients with Hansen's disease was found to harbor dapsone-resistant Mycobacterium leprae. That single strain was only partially resistant, ie, it was resistant to 0.0001% dapsone in a mouse diet but not to higher concentrations. During the years 1983 through 1988, M leprae from 47 previously untreated patients presenting to clinics in San Francisco, Calif, and Los Angeles, Calif, grew in mice. None of these strains was found to be dapsone resistant. Thus, from 1978 through 1988 only one of 101 M leprae isolates obtained from skin biopsy specimens from patients with leprosy was found to be resistant to dapsone. We have concluded that primary dapsone resistance still does not appear to be a significant problem in California. Owing to the fact that our single resistant case and those reported from international sources are, in general, partially resistant, the potential importance of partial dapsone resistance is discussed.

Reconstitution of Mycobacterium leprae immunity in severe combined immunodeficient mice using a T-cell line

To test whether Mycobacterium leprae-immune T cells can confer protection against infection with leprosy bacilli, severe combined immunodeficient (SCID) mice were reconstituted with a BALB/c-derived, M. leprae-responsive, T-cell line. Flow cytometric analysis of spleen and peripheral blood cells confirmed reconstitution with T cells. In vitro lymphokine production and the proliferation of spleen cells from the reconstituted animals established that the donor cells had maintained their functional activity for the duration of the study (275 days). The transfer of immune T cells 24 hr before foot pad infection with leprosy bacilli resulted in a profound reduction in M. leprae multiplication, as compared to the nonreconstituted SCID mice. The yield of acid-fast bacilli in the foot pads of SCID mice reconstituted with the M. leprae-immune T cells also was significantly lower than that found in naive BALB/c mice, and at levels previously found only in BALB/c mice that had been immunized effectively. These experiments demonstrate that M. leprae-immune T cells home effectively and control M. leprae infection in SCID mice.