Cutaneous Respirometry as Novel Technique to Monitor Mitochondrial Function: A Feasibility Study in Healthy Volunteers

BackgroundThe protoporphyrin IX-triplet state lifetime technique (PpIX-TSLT) is proposed as a potential clinical non-invasive tool to monitor mitochondrial function. This technique has been evaluated in several animal studies. Mitochondrial respirometry allows measurement in vivo of mitochondrial oxygen tension (mitoPO₂) and mitochondrial oxygen consumption (mitoVO₂) in skin. This study describes the first use of a clinical prototype in skin of humans.MethodsThe clinical prototype was tested in 30 healthy volunteers. A self-adhesive patch containing 2 mg 5-aminolevulinic acid (ALA) was applied on the skin of the anterior chest wall (sternal) for induction of mitochondrial protoporphyrin IX and was protected from light for 5 h. MitoPO₂ was measured by means of oxygen-dependent delayed fluorescence of protoporphyrin IX. MitoVO₂ was determined by dynamic mitoPO₂ measurements on the primed skin, while locally blocking oxygen supply by applying local pressure with the measurement probe. MitoPO₂ was recorded before and during a 60-s period of compression of the microcirculation, at an interval of 1 Hz. Oxygen consumption (i.e. the local oxygen disappearance rate) was calculated from the decay of the mitoPO₂ slope.ResultsOxygen-dependent delayed fluorescence measurements were successfully performed in the skin of 27 volunteers. The average value (± SD) of mitoPO₂ was 44 ± 17 mmHg and mean mitoVO₂ values were 5.8 ± 2.3 and 6.1 ± 1.6 mmHg s^-1 at a skin temperature of 34°C and 40°C, respectively. No major discomfort during measurement and no long-term dermatological abnormalities were reported in a survey performed 1 month after measurements.ConclusionThese results show that the clinical prototype allows measurement of mitochondrial oxygenation and oxygen consumption in humans. The development of this clinically applicable device offers opportunities for further evaluation of the technique in humans and the start of first clinical studies.     

Microvascular and mitochondrial PO2 simultaneously measured by oxygen‐dependent delayed luminescence

Measurement of tissue oxygenation is a complex task and various techniques have led to a wide range of tissue PO₂ values and contradictory results. Tissue is compartmentalized in microcirculation, interstitium and intracellular space and current techniques are biased towards a certain compartment. Simultaneous oxygen measurements in various compartments might be of great benefit for our understanding of determinants of tissue oxygenation. Here we report simultaneous measurement of microvascular PO₂ (μPO₂) and mitochondrial PO₂ (mitoPO₂) in rats. The μPO₂ measurements are based on oxygen‐dependent quenching of phosphorescence of the near‐infrared phosphor Oxyphor G2. The mitoPO₂ measurements are based on oxygen‐dependent quenching of delayed fluorescence of protoporphyrin IX (PpIX). Favorable spectral properties of these porphyrins allow simultaneous measurement of the delayed luminescence lifetimes. A dedicated fiber‐based time‐domain setup consisting of a tunable pulsed laser, 2 red‐sensitive gated photomultiplier tubes and a simultaneous sampling data‐acquisition system is described in detail. The absence of cross talk between the channels is shown and the feasibility of simultaneous μPO₂ and mitoPO₂ measurements is demonstrated in rat liver in vivo. It is anticipated that this novel approach will greatly contribute to our understanding of tissue oxygenation in physiological and pathological circumstances. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Increased in vivo mitochondrial oxygenation with right ventricular failure induced by pulmonary arterial hypertension: mitochondrial inhibition as driver of cardiac failure?

Background

The leading cause of mortality due to pulmonary arterial hypertension (PAH) is failure of the cardiac right ventricle. It has long been hypothesized that during the development of chronic cardiac failure the heart becomes energy deprived, possibly due to shortage of oxygen at the level of cardiomyocyte mitochondria. However, direct evaluation of oxygen tension levels within the in vivo right ventricle during PAH is currently lacking. Here we directly evaluated this hypothesis by using a recently reported technique of oxygen-dependent quenching of delayed fluorescence of mitochondrial protoprophyrin IX, to determine the distribution of mitochondrial oxygen tension (mitoPO₂) within the right ventricle (RV) subjected to progressive PAH.

Methods

PAH was induced through a single injection of monocrotaline (MCT). Control (saline-injected), compensated RV hypertrophy (30 mg/kg MCT; MCT30), and RV failure (60 mg/kg MCT; MCT60) rats were compared 4 wk after treatment. The distribution of mitoPO₂ within the RV was determined in mechanically-ventilated, anaesthetized animals, applying different inspired oxygen (FiO₂) levels and two increment dosages of dobutamine.

Results

MCT60 resulted in RV failure (increased mortality, weight loss, increased lung weight), MCT30 resulted in compensated RV hypertrophy. At 30% or 40% FiO₂, necessary to obtain physiological arterial PO₂ in the diseased animals, RV failure rats had significantly less mitochondria (15% of total mitochondria) in the 0-20 mmHg mitoPO₂ range than hypertrophied RV rats (48%) or control rats (54%). Only when oxygen supply was reduced to 21% FiO_2, resulting in low arterial PO₂ for the MCT60 animals, or when oxygen demand increased with high dose dobutamine, the number of failing RV mitochondria with low oxygen became similar to control RV. In addition, metabolic enzyme analysis revealed similar mitochondrial mass, increased glycolytic hexokinase activity following MCT, with increased lactate dehydrogenase activity only in compensated hypertrophied RV.

Conclusions

Our novel observation of increased mitochondrial oxygenation suggests down-regulation of in vivo mitochondrial oxygen consumption, in the absence of hypoxia, with transition towards right ventricular failure induced by pulmonary arterial hypertension.     

Cutaneous respirometry by dynamic measurement of mitochondrial oxygen tension for monitoring mitochondrial function in vivo

Progress in diagnosis and treatment of mitochondrial dysfunction in chronic and acute disease could greatly benefit from techniques for monitoring of mitochondrial function in vivo. In this study we demonstrate the feasibility of in vivo respirometry in skin. Mitochondrial oxygen measurements by means of oxygen-dependent delayed fluorescence of protoporphyrin IX are shown to provide a robust basis for measurement of local oxygen disappearance rate (ODR). The fundamental principles behind the technology are described, together with an analysis method for retrievel of respirometry data. The feasibility and reproducibility of this clinically useful approach are demonstrated in a series of rats.     

Reducing mitochondrial bound hexokinase II mediates transition from non-injurious into injurious ischemia/reperfusion of the intact heart

Ischemia/reperfusion (I/R) of the heart becomes injurious when duration of the ischemic insult exceeds a certain threshold (approximately ≥20 min). Mitochondrial bound hexokinase II (mtHKII) protects against I/R injury, with the amount of mtHKII correlating with injury. Here, we examine whether mtHKII can induce the transition from non-injurious to injurious I/R, by detaching HKII from mitochondria during a non-injurious I/R interval. Additionally, we examine possible underlying mechanisms (increased reactive oxygen species (ROS), increased oxygen consumption (MVO₂) and decreased cardiac energetics) associated with this transition. Langendorff perfused rat hearts were treated for 20 min with saline, TAT-only or 200 nM TAT-HKII, a peptide that translocates HKII from mitochondria. Then, hearts were exposed to non-injurious 15-min ischemia, followed by 30-min reperfusion. I/R injury was determined by necrosis (LDH release) and cardiac mechanical recovery. ROS were measured by DHE fluorescence. Changes in cardiac respiratory activity (cardiac MVO₂ and efficiency and mitochondrial oxygen tension (mitoPO₂) using protoporphyrin IX) and cardiac energetics (ATP, PCr, ?G_ATP) were determined following peptide treatment. When exposed to 15-min ischemia, control hearts had no necrosis and 85% recovery of function. Conversely, TAT-HKII treatment resulted in significant LDH release and reduced cardiac recovery (25%), indicating injurious I/R. This was associated with increased ROS during ischemia and reperfusion. TAT-HKII treatment reduced MVO₂ and improved energetics (increased PCr) before ischemia, without affecting MVO₂/RPP ratio or mitoPO₂. In conclusion, a reduction in mtHKII turns non-injurious I/R into injurious I/R. Loss of mtHKII was associated with increased ROS during ischemia and reperfusion, but not with increased MVO₂ or decreased cardiac energetics before damage occurs.     

Mitochondrial PO2 measured by delayed fluorescence of endogenous protoporphyrin IX

Molecular oxygen is the primary oxidant in biological systems. The ultimate destination of oxygen in vivo is the mitochondria where it is used in oxidative phosphorylation. The ability of this process to produce an amount of high-energy phosphates adequate to sustain life highly depends on the available amount of oxygen. Despite a vast array of techniques to measure oxygen, major (patho)physiological questions remain unanswered because of the unavailability of quantitative techniques to measure mitochondrial oxygen in situ. Here we demonstrate that mitochondrial PO(2) can be directly measured in living cells by harnessing the delayed fluorescence of endogenous protoporphyrin IX (PpIX), thereby providing a technique with the potential for a wide variety of applications. We applied this technique to different cell lines (V-79 Chinese hamster lung fibroblasts, HeLa cells and IMR 32-K1 neuroblastoma cells) and present the first direct measurements of the oxygen gradient between the mitochondria and the extracellular volume.     

Oxygen‐dependent delayed fluorescence of protoporphyrin IX measured in the stomach and duodenum during upper gastrointestinal endoscopy

Protoporphyrin IX‐triplet state lifetime technique (PpIX‐TSLT) is a method used to measure oxygen (PO₂) in human cells. The aim of this study was to assess the technical feasibility and safety of measuring oxygen‐dependent delayed fluorescence of 5‐aminolevulinic acid (ALA)‐induced PpIX during upper gastrointestinal (GI) endoscopy. Endoscopic delayed fluorescence measurements were performed 4 hours after oral administration of ALA in healthy volunteers. The ALA dose administered was 0, 1, 5 or 20 mg/kg. Measurements were performed at three mucosal spots in the gastric antrum, duodenal bulb and descending duodenum with the catheter above the mucosa and while applying pressure to induce local ischemia and monitor mitochondrial respiration. During two endoscopies, measurements were performed both before and after intravenous administration of butylscopolamine. Delayed fluorescence measurements were successfully performed during all 10 upper GI endoscopies. ALA dose of 5 mg/kg showed adequate signal‐to‐noise ratio (SNR) values >20 without side effects. All pressure measurements showed significant prolongation of delayed fluorescence lifetime compared to measurements performed without pressure (P < .001). Measurements before and after administration of butylscopolamine did not differ significantly in the duodenal bulb and descending duodenum. Measurements of oxygen‐dependent delayed fluorescence of ALA‐induced PpIX in the GI tract during upper GI endoscopy are technically feasible and safe.     

Fluctuation domains in myoglobin. Fluorescence quenching studies

The dynamics of two domains in the myoglobin molecule, close to the heme and inside the protein medium including the surface, are investigated through the study of the fluorescence oxygen quenching of two probes imbedded in the heme pocket: zinc protoporphyrin IX (with a fluorescence lifetime of 2.1 ns) and metal-free protoporphyrin IX (with a fluorescence lifetime of 17.8 ns).     

A pilot study of exercise-induced changes in mitochondrial oxygen metabolism measured by a cellular oxygen metabolism monitor (PICOMET)

Impaired tissue oxygenation is the key pathomechanism in the development of organ dysfunction in shock; mitochondrial impairment can aggravate the condition. However, measuring tissue oxygenation directly and non-invasively still poses a clinical challenge. A novel device (COMET) allows the assessment of mitochondrial oxygen metabolism using the Protoporphyrin IX Triplet State Lifetime Technique (PpIX-TSLT). Critically ill patients, especially in sepsis, often exhibit oedema which may interfere with the COMET measurement. Furthermore, patients' physical activity level differs significantly before and during hospitalisation. Thus, the aim of this study was to identify the effects of physical activity and body composition on mitochondrial oxygen tension (mitoPO₂) and consumption (mitoVO₂) in healthy controls (N = 40). Furthermore, the study tested the repeatability of the COMET variables and identified covariates. Multiple COMET measurements were performed before (T₁, T₂), during and after (T₃, T₄) ergometry. Body composition was assessed by bioimpedance analysis. Physiological variables (blood pressure, heart rate, oxygen saturation) were recorded. In the analytical sample (n = 26), physical activity significantly decreased mitoVO₂; other COMET variables remained unchanged between T₂ and T₃. During ergometry, mitoPO₂ increased significantly. The distribution of body water significantly influenced mitoVO₂. In our setting, the method demonstrated moderate repeatability. Variables of fitness (heart rate recovery, phase angle and physical activity level), signal quality and duration of exposure to 5-aminolevulinic acid (obligatory for PpIX-TSLT) were identified as significant covariates of mitoVO₂. Mitochondrial oxygen delivery (mitoDO₂) was established as a new variable of COMET analysis. Results of this pilot study should be validated in future studies.     

Decrease in mitochondrial energy coupling by thyroid hormones: a physiological effect rather than a pathological hyperthyroidism consequence

The effect of the in vivo thyroid status on mitochondrial membrane potential (ΔΨ_m) in isolated rat hepatocytes was studies by means of a cytofluorimetric technique and the ΔΨ_m-specific probe JC-1. It is shown that the ΔΨ_m level decreases in the order hypothyroid>euthyroid>hyperthyroid. Polarographic measurement of the hepatocyte respiratory rates revealed an opposite trend of values: the highest respiratory rate in hepatocytes from hyperthyroid animals, the lowest in those from hypothyroid ones. This means that mitochondrial energy coupling is highest in hypothyroid hepatocytes and lowest in hyperthyroid hepatocytes. 6-Ketocholestanol added to hepatocytes failed to counterbalance the uncoupling effect of thyroid hormones on ΔΨ_m and respiration rate. Under the same conditions, 6-ketocholestanol appeared to be effective in recoupling of respiration uncoupled by low concentrations of the artificial protonophore FCCP. The mechanism and possible physiological functions of the thyroid hormone-induced decrease in mitochondrial energy coupling are discussed.     

Oxygenation measurement by multi‐wavelength oxygen‐dependent phosphorescence and delayed fluorescence: catchment depth and application in intact heart

Oxygen delivery and metabolism represent key factors for organ function in health and disease. We describe the optical key characteristics of a technique to comprehensively measure oxygen tension (PO₂) in myocardium, using oxygen‐dependent quenching of phosphorescence and delayed fluorescence of porphyrins, by means of Monte Carlo simulations and ex vivo experiments. Oxyphor G2 (microvascular PO₂) was excited at 442 nm and 632 nm and protoporphyrin IX (mitochondrial PO₂) at 510 nm. This resulted in catchment depths of 161 (86) µm, 350 (307) µm and 262 (255) µm respectively, as estimated by Monte Carlo simulations and ex vivo experiments (brackets). The feasibility to detect changes in oxygenation within separate anatomical compartments is demonstrated in rat heart in vivo.

Schematic of ex vivo measurements.     

Protoporphyrin IX accumulation disrupts mitochondrial dynamics and function in ABCG2-deficient hepatocytes

Targeted inhibition of multidrug ABCG2 transporter is believed to improve cancer therapeutics. However, the consequences of ABCG2 inhibition have not been systematically evaluated since ABCG2 is expressed in several organs including the liver. Here, we demonstrate that ABCG2-deficient hepatocytes have increased amounts of fragmental mitochondria accompanied by disruption of mitochondrial dynamics and functions. This disruption was due to ABCG2 knockout elevating intracellular protoporphyrin IX, which led to upregulation of DRP-1-mediated mitochondrial fission. The finding that ABCG2 deficiency can generate dysfunctional mitochondria in hepatocytes raises concerns regarding the systematic use of ABCG2 inhibitor in cancer patients.     

Quantitative determination of localized tissue oxygen concentration in vivo by two-photon excitation phosphorescence lifetime measurements.

This study describes the use of two-photon excitation phosphorescence lifetime measurements for quantitative oxygen determination in vivo. Doubling the excitation wavelength of Pd-porphyrin from visible light to the infrared allows for deeper tissue penetration and a more precise and confined selection of the excitation volume due to the nonlinear two-photon effect. By using a focused laser beam from a 1,064-nm Q-switched laser, providing 10-ns pulses of 10 mJ, albumin-bound Pd-porphyrin was effectively excited and oxygen-dependent decay of phosphorescence was observed. In vitro calibration of phosphorescence lifetime vs. oxygen tension was performed. The obtained calibration constants were kq = 356 Torr(-1) x s(-1) (quenching constant) and tau0 = 550 micros (lifetime at zero-oxygen conditions) at 37 degrees C. The phosphorescence intensity showed a squared dependency to the excitation intensity, typical for two-photon excitation. In vivo demonstration of two-photon excitation phosphorescence lifetime measurements is shown by step-wise PO2 measurements through the cortex of rat kidney. It is concluded that quantitative oxygen measurements can be made, both in vitro and in vivo, using two-photon excitation oxygen-dependent quenching of phosphorescence. The use of two-photon excitation has the potential to lead to new applications of the phosphorescence lifetime technique, e.g., noninvasive oxygen scanning in tissue at high spatial resolution. To our knowledge, this is the first report in which two-photon excitation is used in the setting of oxygen-dependent quenching of phosphorescence lifetime measurements.     

"Mitochondrial" photochemical drugs do not release toxic amounts of 1O(2) within the mitochondrial matrix space

Previously, we demonstrated that mitochondrial NAD(P)H is the primary target of singlet oxygen (1O(2)) generated by photoactivation of mitochondria-selective rhodamine derivatives. Hence, local NAD(P)H oxidation/fluorescence decrease may be used to reveal the site of intracellular 1O(2) generation. Therefore, in addition to the previously used tetramethylrhodamine methylester (TMRM), 2('),4('),5('),7(')-tetrabromorhodamine 123 bromide (TBRB) and rhodamine 123 (Rho 123), we tested here whether mitochondrial NAD(P)H of cultured hepatocytes is directly oxidized upon irradiation of different "mitochondrial" photosensitizers (Photofrin; protoporphyrin IX; Al(III) phthalocyanine chloride tetrasulfonic acid; meso-tetra(4-sulfonatophenyl)porphine dihydrochloride; Visudyne). In contrast to TMRM and Rho 123, which directly oxidized NAD(P)H upon irradiation, irradiation of intracellular TBRB and the photochemical drugs only indirectly affected mitochondrial NAD(P)H due to loss of mitochondrial integrity. In line with this result only TMRM and Rho 123 exclusively localized within the mitochondrial matrix. Due to these results it is doubtful whether real mitochondrial photosensitizers actually exist among the photochemical drugs applicable/used for photodynamic therapy.     

Fluorometric assays for coproporphyrinogen oxidase and protoporphyrinogen oxidase

We describe fluorometric assays for two enzymes of the heme pathway, coproporphyrinogen oxidase and protoporphyrinogen oxidase. Both assays are based on measurement of protoporphyrin IX fluorescence generated from coproporphyrinogen III by the two consecutive reactions catalyzed by coproporphyrinogen oxidase and protoporphyrinogen oxidase. Both enzymatic activities are measured by recording protoporphyrin IX fluorescence increase in air-saturated buffer in the presence of EDTA (to inhibit ferrochelatase that can further metabolize protoporphyrin IX) and in the presence of dithiothreitol (that prevents nonenzymatic oxidation of porphyrinogens to porphyrins). Coproporphyrinogen oxidase (limiting) activity is measured in the presence of a large excess of protoporphyrinogen oxidase provided by yeast mitochondrial membranes isolated from commercial baker's yeast. These membranes are easy to prepare and are stable for at least 1 year when kept at -80 degrees C. Moreover they ensure maximum fluorescence of the generated protoporphyrin (solubilization effect), avoiding use of a detergent in the incubation medium. The fluorometric protoporphyrinogen oxidase two-step assay is closely related to that already described (J.-M. Camadro, D. Urban-Grimal, and P. Labbe, 1982, Biochem. Biophys. Res. Commun. 106, 724-730). Protoporphyrinogen is enzymatically generated from coproporphyrinogen by partially purified yeast coproporphyrinogen oxidase. The protoporphyrinogen oxidase reaction is then initiated by addition of the membrane fraction to be tested. However, when very low amounts of membrane are used, low amounts of Tween 80 (less than 1 mg/ml) have to be added to the incubation mixture to solubilize protoporphyrin IX in order to ensure optimal fluorescence intensity. This detergent has no effect on the rate of the enzymatic reaction when used at concentrations less than 2 mg/ml. Activities ranging from 0.1 to 4-5 nmol protoporphyrin formed per hour per assay are easily and reproducibly measured in less than 30 min.     

Liver Cell Calcium Homeostasis in Carbon Tetrachloride Liver Cell Injury: New Data With Fura21

The calcium fluorescent probe fura2 was used to measure concentration of free calcium in the cytosol of isolated rat hepatocytes in suspension. The resting level in untreated hepatocytes was 121 nM. On addition of CCl₄ at a concentration of 0.5 mM, cytosolic free calcium rose sharply and reached a statistically significant (P<0.05) steady plateau level of about 190 nM within five minutes. With a concentration of 1.0 mM CCl₄, cytosolic free calcium rose within ten minutes to a plateau level of about 200 nM. Use of fura2, along with the capacity of Mn²⁺ ions to effectively quench fura2 fluorescence, provided the basis for a simple and decisive method to determine whether the added CCl₄ was permeabilizing the hepatocyte plasma membrane by direct solvent action. It was found that up to a concentration of 1.0 mM, CCl₄ did not permeabilize the plasma membrane, but direct attack on the plasma membrane was unequivocally demonstrated for concentrations of 2 mM CCl₄ and above. Finally, an hypothesis is presented for resolution of the puzzling dilemma that emerged from the observation, reported from two laboratories, that CCl₄ can rapidly mobilize liver mitochondrial calcium despite the well-known relative resistance of these organelles to the damaging effects of this toxic agent.     

Kinetics of delayed chlorophyll a fluorescence registered in milliseconds time range

Delayed fluorescence dark decays in the time interval from 0.35 to 5.5ms are measured during dark to light adaptation in whole barley leaves and isolated thylakoid membranes, using a disc phosphoroscope. The changes in delayed fluorescence features are compared with variable chlorophyll fluorescence simultaneously registered with the same apparatus as well as in parallel by Handy PEA (Hansatech Instruments Ltd.), and absorbance changes at 820 nm. The registered delayed fluorescence signal is a sum of three components – submillisecond with lifetime of about 0.6 ms, millisecond decayed 2–4 ms and slow component with lifetime > >5.5 ms. The submillisecond delayed fluorescence component is proposed to be a result of radiative charge recombination in Photosystem II reaction centers in the state Z⁺PQ_A⁻Q_B⁻, and its lifetime is determined by the rate of electron transfer from Q_A⁻ to Q_B⁻. The millisecond delayed fluorescence component is associated with recombination in Z⁺PQ_A⁻Q_B⁼ centers with a lifetime determined by the sum of the rate constants of electron transfer from the oxygen-evolving complex to Z⁺ and of the exchange between the reduced and oxidized plastoquinone pool in the Q_B-site. On the basis of these assumptions and of the different share of the three components in the integral delayed fluorescence during induction, an attempt has been made to interpret the changes in the delayed fluorescence intensity during the transition of the photosynthetic apparatus from dark to light adapted state.     

Impairment of the photosynthetic apparatus by oxidative stress induced by photosensitization reaction of protoporphyrin IX

Treatment with the herbicide acifluorfen-sodium (AF-Na), an inhibitor of protoporphyrinogen oxidase, caused an accumulation of protoporphyrin IX (Proto IX) , light-induced necrotic spots on the cucumber cotyledon within 12-24 h, and photobleaching after 48-72 h of light exposure. Proto IX-sensitized and singlet oxygen (¹O₂)-mediated oxidative stress caused by AF-Na treatment impaired photosystem I (PSI), photosystem II (PSII) and whole chain electron transport reactions. As compared to controls, the F_v/F_m (variable to maximal chlorophyll a fluorescence) ratio of treated samples was reduced. The PSII electron donor NH₂OH failed to restore the F_v/F_m ratio suggesting that the reduction of F_v/F_m reflects the loss of reaction center functions. This explanation is further supported by the practically near-similar loss of PSI and PSII activities. As revealed from the light saturation curve (rate of oxygen evolution as a function of light intensity), the reduction of PSII activity was both due to the reduction in the quantum yield at limiting light intensities and impairment of light-saturated electron transport. In treated cotyledons both the Q (due to recombination of Q_A⁻ with S₂) and B (due to recombination of Q_B⁻ with S₂/S₃) band of thermoluminescence decreased by 50% suggesting a loss of active PSII reaction centers. In both the control and treated samples, the thermoluminescence yield of B band exhibited a periodicity of 4 suggesting normal functioning of the S states in centers that were still active. The low temperature (77 K) fluorescence emission spectra revealed that the F₆₉₅ band (that originates in CP-47) increased probably due to reduced energy transfer from the CP47 to the reaction center. These demonstrated an overall damage to the PSI and PSII reaction centers by ¹O₂ produced in response to photosensitization reaction of protoporphyrin IX in AF-Na-treated cucumber seedlings.     

Enzymatic reduction of synthetic polymer-bound hemin derivatives: efficient method to prepare a heme-oxygen adduct in cooled aqueous medium

Synthetic polymer-bound hemin (iron(III) protoporphyrin IX) derivatives were effectively reduced by ferredoxin and ferredoxin-NADP reductase system. The resultant polymer-bound heme (iron(II) protoporphyrin IX) derivatives formed oxygen adducts with a lifetime of ca. 1 hr in aqueous solution at -30 degrees C. The reduction rate is discussed in terms of the structure of the hemin derivatives.     

Separation of Mg-Protoporphyrin IX and Mg-Protoporphyrin IX Monomethyl Ester Synthesized de novo by Developing Cucumber Etioplasts

High pressure liquid chromatography was used to demonstrate that chelation of Mg²⁺ into protoporphyrin IX precedes methylation in isolated greening etioplasts from cucumber (Cucumis sativus L. var. Beit Alpha) cotyledons. Mg-protoporphyrin IX synthesized in vitro from protoporphyrin IX, Mg²⁺, and ATP or exogenous Mg-protoporphyrin IX could serve as substrates for the methylation step. In either case, S-adenosylmethionine was the methyl donor and could not be replaced by ATP plus methionine.