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PubMed2005

Inactivation of viruses in platelet concentrates by photochemical treatment with amotosalen and long-wavelength ultraviolet light.

BACKGROUND: Viral contamination of platelet (PLT) concentrates can result in transfusion-transmitted diseases. A photochemical treatment (PCT) process with amotosalen-HCl and long-wavelength ultraviolet light (UVA), which cross-links nucleic acids, was developed to inactivate viruses and other pathogens in PLT concentrates. STUDY DESIGN AND METHODS: High titers of pathogenic or blood-borne viruses, representing 10 different families, were added to single-donor PLT concentrates containing 3.0 x 10(11) to 6.0 x 10(11) PLTs in approximately 300 mL of 35 percent plasma and 65 percent PLT additive solution (InterSol). After PCT with 150 micromol per L amotosalen and 3 J per cm(2) UVA, residual viral infectivity was assayed by sensitive cell culture or animal systems. RESULTS: Enveloped viruses were uniformly sensitive to inactivation by PCT whereas nonenveloped viruses demonstrated variable inactivation. Log reduction of enveloped viruses for cell-free HIV-1 was >6.2; for cell-associated HIV-1, >6.1; for clinical isolate HIV-1, >3.4; for clinical isolate HIV-2, >2.5; for HBV, >5.5; for HCV, >4.5; for DHBV, >6.2; for BVDV, >6.0; for HTLV-I, 4.2; for HTLV-II, 4.6; for CMV, >5.9; for WNV, >5.5; for SARS-HCoV, >5.8; and for vaccinia virus, >4.7. Log reduction of nonenveloped viruses for human adenovirus 5 was >5.2; for parvovirus B19, 3.5->5.0; for bluetongue virus, 5.6-5.9; for feline conjunctivitis virus, 1.7-2.4; and for simian adenovirus 15, 0.7-2.3. CONCLUSION: PCT inactivates a broad spectrum of pathogenic, blood-borne viruses. Inactivation of viruses in PLT concentrates with amotosalen and UVA offers the potential to prospectively prevent the majority of PLT transfusion-associated viral diseases.

Blood Banking↗

PubMed2004

Photochemical treatment of platelet concentrates with amotosalen hydrochloride and ultraviolet A light inactivates free and latent cytomegalovirus in a murine transfusion model.

BACKGROUND: A photochemical treatment (PCT) process utilizing amotosalen hydrochloride and long wavelength UVA light has been developed to inactivate pathogens in PLTs. This study investigated the effects of amotosalen/UVA treatment on free and latent murine CMV (MCMV) in PLT preparations using a murine model of transfusion-transmitted CMV (TT-CMV). STUDY DESIGN AND METHODS: In a model of latent MCMV infection, "donor" mice received 1 x 10(6) plaque-forming units (PFUs) MCMV and were rested 14 days. Subsequently harvested, pooled, and washed WBCs were PCR positive for MCMV. Murine WBC doses of 1 x 10(4), 1 x 10(5), and 1 x 10(6) were added to human apheresis PLTs in 35 percent autologous plasma and 65 percent PLT AS (PAS). The WBC-PLT products were treated with 150 micro mol/L amotosalen and 0.6 J per cm2 UVA and transfused via tail vein injection into recipient mice. Recipients were killed on Day 14. Blood and spleens were collected and assayed for MCMV by PCR. In a parallel model of active infection with free virus, human PLT in 35 percent autologous plasma and 65 percent PAS were dosed with 1 x 10(5) and 1 x 10(6) PFUs of MCMV. All other procedures were as described above. RESULTS: In the absence of amotosalen/UVA-pretreatment, transfusion of PLT latently or actively infected with MCMV produced TT-CMV in a dose-dependent fashion. In contrast, all transfusion recipients of identical PLT preparations pretreated with amotosalen/UVA were uniformly PCR negative for MCMV (abrogation of TT-CMV; p < 0.05). CONCLUSIONS: PCT of PLT preparations with the specified doses of amotosalen hydrochloride and UVA light prevents transfusion transmission of free and latent MCMV in a murine model. These results suggest that PCT of human PLTs with amotosalen/UVA should also effectively abrogate TT-CMV in the clinical setting.

Animals↗

PubMed2004

Photochemical treatment of platelet concentrates with amotosalen and long-wavelength ultraviolet light inactivates a broad spectrum of pathogenic bacteria.

BACKGROUND: Bacterial contamination of platelet (PLT) concentrates can result in transfusion-transmitted sepsis. A photochemical treatment (PCT) process with amotosalen HCl and long-wavelength ultraviolet light (UVA), which cross-links nucleic acids, was developed to inactivate bacteria and other pathogens in PLT concentrates. STUDY DESIGN AND METHODS: High titers of pathogenic aerobic and anaerobic Gram-positive bacteria (10 species), aerobic Gram-negative bacteria (7 species), and spirochetes (2 species) were added to single-donor PLT concentrates containing 3.0 x 10(11) to 6.0 x 10(11) PLTs in approximately 300 mL of 35 percent plasma and 65 percent PLT additive solution (InterSol, Baxter Healthcare) or saline. After PCT with 150 micro mol per L amotosalen and 3 J per cm(2) UVA, residual bacterial levels were detected by sensitive microbiologic methods. RESULTS: The level of inactivation of viable bacteria was expressed as log reduction. Log reduction of Gram-positive bacteria for Staphylococcus epidermidis was > 6.6; for Staphylococcus aureus, 6.6; for Streptococcus pyogenes, > 6.8; for Listeria monocytogenes, > 6.3; for Corynebacterium minutissimum, > 6.3; for Bacillus cereus (vegetative), > 5.5; for Lactobacillus sp., > 6.4; for Bifidobacterium adolescentis, > 6.0; for Propionibacterium acnes, > 6.2; and for Clostridium perfringens, > 6.5. Log reduction of Gram-negative bacteria for Escherichia coli was > 6.4; for Serratia marcescens, > 6.7; for Klebsiella pneumoniae, > 5.6; for Pseudomonas aeruginosa, 4.5; for Salmonella choleraesuis, > 6.2; for Yersinia enterocolitica, > 5.9; and for Enterobacter cloacae, 5.9. Log reduction of spirochetes for Treponema pallidum was 6.8 to 7.0, and for Borrelia burgdorferi, > 6.9. CONCLUSION: PCT inactivates high levels of a broad spectrum of pathogenic bacteria. The inactivation of bacteria in PLT concentrates offers the potential to prospectively prevent PLT-transfusion-associated bacteremia.

Bacteremia↗

PubMed2005

Amotosalen interactions with platelet and plasma components: absence of neoantigen formation after photochemical treatment.

BACKGROUND: The INTERCEPT Blood System (Baxter Healthcare Corp., and Cerus Corp.) is a photochemical treatment (PCT) process that uses amotosalen (S-59) and ultraviolet A (UVA) illumination to inactivate a broad spectrum of pathogens. STUDY DESIGN AND METHODS: To evaluate the potential of the process to create neoantigens, the amounts of residual amotosalen and photoproducts present in PCT platelets (PLTs) and PCT plasma were quantified. The initial amount of amotosalen was 150 micromol per L. After illumination with 3 J per cm2 UVA and before transfusion, a compound adsorption device was used to substantially reduce the amounts of free amotosalen and unreactive photodegradation products. Patient serum samples from Phase III clinical trials were assayed by enzyme-linked immunosorbent assay (ELISA) for antibodies to potential amotosalen neoantigens. RESULTS: After PCT, 15 percent of the starting amount of amotosalen remains bound to PLTs, and 15 to 22 percent remains bound to plasma components. The majority of bound amotosalen is associated with lipid. Less than 1 percent of PLT-bound amotosalen and approximately 2 percent of plasma-bound amotosalen can be extracted into the water-soluble protein fraction. In seven Phase III clinical trials, 523 patients received more than 8000 units of PCT PLTs or PCT plasma. None of the patients exhibited clinical or laboratory manifestations of neoantigenicity. Furthermore, no other alteration of PLT membrane proteins was identified based on testing for lymphocytotoxic antibodies and PLT-specific alloantibodies. CONCLUSION: These results indicate that no neoantigens were detected by ELISA after PCT, suggesting that transfusion of PCT PLTs or PCT plasma does not induce adverse immunologic responses.

Antilymphocyte Serum↗

PubMed2006

Photochemical treatment of plasma with amotosalen and long-wavelength ultraviolet light inactivates pathogens while retaining coagulation function.

BACKGROUND: The INTERCEPT Blood System, a photochemical treatment (PCT) process, has been developed to inactivate pathogens in platelet concentrates. These studies evaluated the efficacy of PCT to inactivate pathogens in plasma and the effect of PCT on plasma function. STUDY DESIGN AND METHODS: Jumbo (600 mL) plasma units were inoculated with high titers of test pathogens and treated with 150 micromol per L amotosalen and 3 J per cm(2) long-wavelength ultraviolet light. The viability of each pathogen before and after treatment was measured with biological assays. Plasma function was evaluated through measurement of coagulation factors and antithrombotic protein activities. RESULTS: The levels of inactivation expressed as log-reduction were as follows: cell-free human immunodeficiency virus-1 (HIV-1), greater than 6.8; cell-associated HIV-1, greater than 6.4; human T-lymphotropic virus-I (HTLV-I), 4.5; HTLV-II, greater than 5.7; hepatitis B virus (HBV) and hepatitis C virus, greater than 4.5; duck HBV, 4.4 to 4.5; bovine viral diarrhea virus, 6.0; severe acute respiratory syndrome coronavirus, 5.5; West Nile virus, 6.8; bluetongue virus, 5.1; human adenovirus 5, 6.8; Klebsiella pneumoniae, greater than 7.4; Staphylococcus epidermidis and Yersinia enterocolitica, greater than 7.3; Treponema pallidum, greater than 5.9; Borrelia burgdorferi, greater than 10.6; Plasmodium falciparum, 6.9; Trypanosoma cruzi, greater than 5.0; and Babesia microti, greater than 5.3. Retention of coagulation factor activity after PCT was expressed as the proportion of pretreatment (baseline) activity. Retention was 72 to 73 percent of baseline fibrinogen and Factor (F)VIII activity and 78 to 98 percent for FII, FV, FVII, F IX, FX, FXI, FXIII, protein C, protein S, antithrombin, and alpha2-antiplasmin. CONCLUSION: PCT of plasma inactivated high levels of a wide range of pathogens while maintaining adequate coagulation function. PCT has the potential to reduce the risk of transfusion-transmitted diseases in patients requiring plasma transfusion support.

Animals↗

PubMed2000

Functional characteristics of S-59 photochemically treated platelet concentrates derived from buffy coats.

BACKGROUND: A photochemical treatment (PCT) process for inactivation of infectious pathogens and leukocytes has been developed and evaluated using single-donor platelet concentrates. This study assessed the application of PCT to platelets prepared from pooled buffy coats. In this study, in vitro functional characteristics of PCT platelets were compared to control platelets prepared from pooled buffy coats using the approved platelet-additive solution T-Sol((R)). Platelets in platelet PAS III additive solution without PCT were evaluated as well. PCT also included the use of a psoralen (S-59) reduction device (SRD). MATERIALS AND METHODS: Four types of platelet concentrates were compared: (1) platelet concentrate in plasma/T-Sol; (2) platelet concentrate in plasma/PAS III; (3) platelet concentrate in plasma/PAS III, PCT, 9 h SRD and (4) platelet concentrate in plasma/PAS III, PCT, 16 h SRD. PCT occurred on the day after whole-blood collection. In vitro assay parameters included: pH, pO(2), pCO(2), HCO(-)(3), platelet count, mean platelet volume, plasma glucose, plasma lactate, total ATP, expression of p-selectin, hypotonic shock response and electron microscopy. RESULTS: The results indicate that PCT is compatible with platelet concentrates prepared from pooled buffy coats for up to 7 days of storage. CONCLUSION: The PCT process resulted in acceptable in vitro platelet functional characteristics and is currently in clinical trials to evaluate the haemostatic efficacy of PCT platelets in thrombocytopenic patients requiring multiple platelet transfusions.

Blood Platelets↗

PubMed2006

Photochemically treated fresh frozen plasma for transfusion of patients with acquired coagulopathy of liver disease.

An ex vivo photochemical treatment (PCT) process was developed to inactivate pathogens in fresh frozen plasma (PCT-FFP). A prospective, controlled, double-blinded, randomized study was conducted to evaluate the efficacy and safety of PCT-FFP compared with conventional FFP (C-FFP). Patients (n = 121) with acquired coagulopathy, largely due to liver disease, including hepatic transplantation, were transfused with either PCT-FFP or C-FFP for up to 7 days. Primary end points were changes in the prothrombin time (PT) and the partial thromboplastin time (PTT) in response to the first FFP transfusion. Secondary analyses compared changes in the PT and the PTT, factor VII levels, clinical hemostasis, blood component usage, and safety following FFP transfusions for up to 7 days. Following the first transfusion, correction in the PT and PTT adjusted for FFP dose and patient weight was not different. Changes in the PT were equivalent between treatment groups (P = .002 by noninferiority). Equivalence was not demonstrated for changes in the PTT. Following multiple transfusions, correction of the PT and the PTT was similar between groups. No differences were observed in use of blood components, clinical hemostasis, or safety. These results suggest PCT-FFP supported hemostasis in the treatment of acquired coagulopathy similarly to conventional FFP.

Aged↗

PubMed1999

Damage to rat retinal DNA induced in vivo by visible light.

Intense visible light can damage retinal photoreceptor cells by photochemical or thermal processes, leading to cell death. The precise mechanism of light-induced damage is unknown; however, oxidative stress is thought to be involved, based on the protective effect of antioxidants on the light-exposed retina. To explore the in vivo effects of light on retinal DNA, rats were exposed to intense visible light for up to 24 h and the time courses of single-strand breaks in restriction fragments containing the opsin, insulin 1 and interleukin-6 genes were measured. All three gene fragments displayed increasing single-strand modifications with increasing light exposure. Treatment with the antioxidant dimethylthiourea prior to light exposure delayed the development of net damage. The time course of double-strand DNA damage was also examined in specific genes and in repetitive DNA. The appearance of discrete 140-200 base-pair DNA fragments after 20 h of light exposure implicated a nonrandom, possibly enzymatic damaging mechanism. The generation of nucleosome core-sized DNA fragments, in conjunction with single-strand breaks, suggests two phases of light-induced retinal damage, with random attack on DNA by activated oxygen species preceding enzymatic degradation.

Animals↗

PubMedDate not supplied

Photodynamic therapy: an update.

Photodynamic therapy (PDT) is a promising local treatment modality based on the selective accumulation of a photosensitizer in malignant tissues and the subsequent irradiation with laser light. Photodynamic therapy of malignant tumors includes biological, photochemical and photophysical processes. These processes involve: (a) absorption of photosensitizing agent; (b) selective retention of the photosensitizer in tumors and (c) irradiation of sensitized tumor by laser radiation. This report provides a review of photosensitizers, photochemistry, subcellular targets, side effects and laser involved in photodynamic therapy. In addition, gradual increase in knowledge related to in vitro and in vivo mechanisms of action of PDT, as well as some clinical applications of photodynamic therapy are presented.

Aminolevulinic Acid↗

PubMed2002

[pH sensors based on rubbery ormosils preparation and their spectrum studies].

A new type of methyl substituted ormosils as a matrix for bromophenol blue (BPhB) and bromocresol green (BCG) is described. The new ormosils combine features of classical TEOS sol-gel material such as solvability in organic solvent and those of sol-gel glasses such as transparent and a porous structure, the ormosils also make a good mechanical stability. The influence of the conditions during the polymerisation process on the photochemical properties of BPhB and BCG has been studied. This sol-gel material was wed to immobilize pH-sensitive absorption dyes, bromothymol blue and bromocresol green, to prepare pH sensing films. The several aspects of the sensing films, including the leaching of the dye from gel, response time to different pH buffer solution, absorption spectra and the improvement of the immobilization of the dyes to filmo, were also discussed.

English Abstract↗

PubMed1992

[Transduction of the visual signal in retinal cells].

Transduction of a visual signal is a complex process. It involves photochemical, enzymatic and ionic reactions. An electrophysiological response is generated on absorption of a photon by a photoreceptor cell's pigment molecule, then propagates to the synapses. The first photochemical reaction, isomerization of retinal, in vertebrates occurs in the photoreceptor cells--rods and cones--of the retina, so changes conformation and activity of a pigment-bound protein, rhodopsin, in membranes of intracellular discs. Rhodopsin becomes enzymatically active and catalyses the activation by GTP of a great number of transducins, which in turn activate cGMP phosphodiesterase. This enzymatic chain propagates and greatly enhances hydrolysis of cytoplasmic cGMP. One photon incites hydrolysis of 10(5) cGMP molecules in 100 ms. Local cGMP decrease frees it from specific binding sites in cytoplasm occupied by proteinaceous canals in cell membrane around the activated disc. In darkness high cGMP concentration, hence binding, kept canals open, maintaining high cellular cation permeability, especially to Na+, and a strong cellular depolarization. Ca2+ influx, also allowed, balanced Na+ movement. Canal closure induces local hyperpolarization, the first electrophysiological response, which propagates through the cell to synaptic contacts. It also lowers intracellular Ca2+ concentration which initiates cGMP synthesis--from GTP by a guanylate cyclase controlled negatively by recoverin, a calcium-dependent protein--to restore cGMP towards at rest level. Although all macromolecules involved in this now fairly complete scheme have been isolated and characterized, cloned and sequenced, no three-dimensional structure has yet been established. The proteins are membrane-bound rather than in independent crystal form, which renders such structural studies difficult.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Photodynamic therapy and some clinical applications in oncology.

Photodynamic therapy (PDT), a new treatment modality for localized cancers involving the selective interaction of visible light with photosensitizers, such as hematoporphyrin derivatives (HpD) or dihematoporphyrin ether/ester (DHE) (Photofrin II). Photodynamic therapy of malignant tumors includes biological, photochemical and photophysical processes. These processes involve: (i) absorption of photosensitizing agent; (ii) selective retention of photosensitizer in tumors and (iii) irradiation of sensitized tumor by laser irradiation. This paper provides a review of photosensitizers, photochemistry, subcellular targets, side effects and lasers involved in photodynamic therapy. In addition, gradual increase in knowledge related to in vivo and in vitro mechanisms of action of PDT, as well as some clinical applications of photodynamic therapy are presented.

Humans↗

PubMed2004

Influence of light and temperature on the stability of procaine hydrochloride injection.

AIM: To study the influence of light and heat on the stability of procaine hydrochloride injection. METHODS: Accelerated tests upon exposure to light at high temperatures were employed. RESULTS: In experiments with either isothermal heating or exposure to light at high temperatures, the drug degradation rate obeys first-order kinetics. The total rate constant, ktotal, caused by both light and heat can be divided into two parts: ktotal = kdark + klight, where kdark and klight are the rate constants caused by heat and light, respectively. The klight can be expressed as klight = Alight x E x exp(-Ea,light/RT). Where E is the illuminance of light, Alight is an experimental constant related to light sources, and Ea,light is an experimental constant. CONCLUSION: Because the form of klight is similar to the Arrhenius equation, it is suggested that Ea,light might be the observed activation energy of the rate-determining step of the subsequent processes of the photochemical reaction. This viewpoint is supported by the fact that the Ea,light is independent of light sources.

Drug Stability↗

PubMed1990

Laser (two-quantum) photolysis of polynucleotides and nucleoproteins: quantitative processing of results.

The paper offers and substantiates a technique for quantitative processing of the photochemical reactions in polynucleotides, nucleoproteins and their components caused by the action of powerful ultraviolet laser pulse radiation.

Lasers↗

PubMed1978

Retinal mechanisms of visual adaptation and afterimages.

Recent results obtained from recordings of isolated photoreceptor activity and from correlations of this activity with time-dependent changes in the responses of other retinal cells in several vertebrates have made a thorough revision of former theories of visual adaptation necessary. The present paper reviews the current state of research and relates the new discoveries with psychophysical findings in an attempt to explain human light and dark adaptation from the novel starting point. The former conceptions of adaptation have to be replaced with a three-level process consisting of photochemical receptor neural and network adaptation. Several adaptive mechanisms can be discerned at each level. Depending on adaptation conditions, any level of the three can play a dominating role and can also produce afterimages that display the behaviour of the mechanisms working at each level. The total achievement of visual adaptation is an optimized end product of the actions of all the various mechanisms.

Adaptation, Ocular↗

PubMed1998

Inactivation of leukocytes in platelet concentrates by photochemical treatment with psoralen plus UVA.

A photochemical treatment (PCT) process using a novel psoralen and long wavelength ultraviolet light (UVA, 320-400 nm) has been developed to inactivate bacteria and viruses in platelet concentrates. This study evaluated the efficacy of PCT for inactivation of leukocytes that contaminate platelet preparations. Three psoralens, 8-methoxypsoralen (8-MOP), 4'-aminomethyl 4,5', 8-trimethylpsoralen (AMT), and the novel psoralen S-59, were compared using the following four independent but complementary biological and molecular assays. (1) T-cell viability: Treatment with 150 mumol/L S-59 and 1.0 to 3.0 Joules/cm2 UVA inactivated >5.4 +/- 0.3 log10 of T cells in full-sized single-donor plateletpheresis units. Using 1.0 Joule/cm2 UVA, the lowest dose of S-59, AMT and 8-MOP required to reduce the number of T cells to the limit of detection was 0.05 micromol/L, 1.0 micromol/L, and 10.0 micromol/L, respectively. (2) Cytokine synthesis: Treatment with 1.9 Joules/cm2 UVA and 150 micromol/L S-59 or AMT completely inhibited synthesis of the cytokine IL-8 by contaminating leukocytes during 5 days of platelet storage. After treatment with 75 micromol/L 8-MOP and 1.9 Joules/cm2 UVA, only low levels of IL-8 were detected. (3) Psoralen-DNA adduct formation: The combination of 1.9 Joules/cm2 UVA and 150 micromol/L S-59, AMT, or 8-MOP induced 12.0 +/- 3.0, 6.0 +/- 0. 9, and 0.7 psoralen adducts per 1,000 bp DNA, respectively. (4) Replication competence: Polymerase chain reaction (PCR) amplification of small genomic DNA sequences (242-439 bp) after PCT was inhibited. The degree of PCR amplification inhibition correlated with the level of adduct formation (S-59 > AMT > 8-MOP). In contrast, 2,500 cGy gamma radiation, a dose that inactivates >5 log10 of T cells in blood products, had minimal effect on cytokine synthesis and did not induce sufficient DNA strand breaks to inhibit PCR amplification of the same small DNA sequences. These results demonstrate that leukocytes are sensitive to PCT with psoralens and among the psoralens tested S-59 is the most effective. Therefore, PCT has the potential to reduce the incidence of leukocyte-mediated adverse immune reactions associated with platelet transfusion.

Adult↗

PubMed1998

Triplet photochemistry of suprofen in aqueous environment and in the beta-cyclodextrin inclusion complex.

The photodecarboxylation of suprofen in the carboxylate form was studied in aqueous medium as a function of the temperature, the concentration and the presence of oxygen by steady-state and time-resolved photochemical techniques. The process is characterized by an activation energy of 9-10 kcal/mol, the precursor state being the lowest triplet which is of pi-pi* nature. The reactivity of the drug was also studied in the beta-cyclodextrin inclusion complex and an additional photoreaction involving the macrocycle as reactive species was observed. Representative NMR and circular dichroism measurements were performed. Singlet molecular oxygen formation was also investigated.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1979

Photoisomerization, energy storage, and charge separation: a model for light energy transduction in visual pigments and bacteriorhodopsin.

A simple model for the early events in visual pigments and bacteriorhodopsin is proposed. The model makes use of the likelihood that a negatively charged amino acid forms a salt bridge with the positively charged nitrogen of the retinylic chromophore. The photochemical event is a cis-trans isomerization in visual pigments and a trans-cis isomerization in bacteriorhodopsin, which in each case cleaves the salt bridge and thus separates charge in the interior of the protein. We propose that this is how the energy of a photon is transduced into chemical free energy of the primary photoproduct. The use of photoisomerization of a flexible chromophore to achieve charge separation provides a general mechanism which may be applicable to other systems. Our model explains many of the fundamental properties of visual pigments and their photoproducts. First, the extraordinarily low rate of thermally populating the ground state of the primary photoproduct, as determined from psychophysical and electrophysiological measurements, is seen as resulting from the large barrier to thermal isomerization about a double bond, perhaps enhanced by electrostatic attraction in the salt bridge. Second, the increase in energy and the spectral red shift that characterize the primary photochemical events are natural consequences of the separation of charge. Proton-dependent processes detected with picosecond techniques are proposed to be ground-state relaxation processes following the primary photochemical event. Finally, the charged groups of the salt bridge, repositioned by photoisomerization, provide a simple mechanism for vectorial proton translocation in bacteriorhodopsin.

Bacteriorhodopsins↗