Post liver transplantation delirium assessment using the CAM-ICU-7 scale: A cohort analysis

Background

We applied the Confusion Assessment Method (CAM)-Intensive Care Unit (ICU)-7 delirium scale to patients who underwent liver transplant (LT).

Methods

Retrospective cohort including patients who underwent LT for cirrhosis admitted to the ICU from June 2013 to June 2016 at the University of Alberta Hospital, Canada. Delirium was assessed using the CAM-ICU-7 scale (0-7 points) twice daily on days one and 3 post LT, with the highest score being considered. Primary endpoint was hospital mortality.

Results

Among all patients, 101/150 (67.3%) were men and mean age was 52.4 (SD 11.8) years. On days 1 and 3 post LT, mean CAM-ICU-7 scores were 1.8 (SD 1.3) and 1.6 (SD 1.8), respectively. Therefore, on days 1 and 3 post LT, 38/150 (25.3%) and 26/95 (27.4%) patients had delirium. While delirium on day 3 post LT was associated with higher hospital mortality (11.5% versus 0%; p = 0.019), it was not associated with length-of-hospital stay (29.2 versus 34.4 days; p = 0.36). Following adjustment for APACHEII score, delirium on day 3 post LT was associated with higher odds of hospital mortality (adjusted odds ratio [aOR] 1.89 [95% CI 1.02-3.50]). Following adjustment for Glasgow Coma Scale and mechanical ventilation, serum creatinine was associated with higher odds of delirium on day 3 post LT (aOR 2.02 [95% CI 1.08-3.77]).

Conclusions

Using the CAM-ICU-7 scale, delirium was diagnosed in a fourth of patients who underwent LT. Delirium on day 3 post LT was associated with higher odds of hospital mortality.

Screening for asymptomatic deep vein thrombosis in COVID-19 patients admitted to the medical ward: a cross-sectional study

Purpose

Patients with COVID-19 have an increased risk for venous thrombo-embolism (VTE), especially pulmonary embolism. The exact prevalence of asymptomatic DVT is not known, as is the usefulness of screening for DVT in patients admitted to ward with COVID-19. We have studied the prevalence of asymptomatic DVT.

Methods

We performed a cross-sectional observational multi-center study at four university medical centers in The Netherlands. All adult patients admitted with COVID-19 to a medical ward were eligible for inclusion, including patients who were transferred back from the ICU to the ward. The study protocol consisted of weekly cross-sectional rounds of compression ultrasound.

Results

In total, 125 patients were included in the study. A significant proportion of patients (N = 34 (27%)) had developed a VTE during their admission for COVID-19 before the study ultrasound was performed. In most VTE cases (N = 27 (79%)) this concerned pulmonary embolism. A new asymptomatic DVT was found in 5 of 125 patients (4.0%; 95% CI 1.3–9.1%) (Table 2). Nine patients (7.2%; 95% CI 3.3–13.2%) developed a VTE (all PE) diagnosed within 28 days after the screening US was performed.

Conclusion

We have shown a low prevalence (4%) of newly discovered asymptomatic DVT outside the ICU-setting in COVID-19 patients. Despite this low prevalence, nine patients developed PE (7%) within 28 days after ultrasound. This favors the hypothesis of local thrombus formation in the lungs. Based on our findings and literature, we do not recommend US-screening of asymptomatic patients with COVID-19 admitted to the ward.

The Prediction of In-Hospital Mortality in Decompensated Cirrhosis with Acute-on-Chronic Liver Failure

Acute-on-chronic liver failure (ACLF) is a condition in cirrhosis associated with organ failure (OF) and high short-term mortality. Both the European Association for the Study of the Liver-Chronic Liver Failure (EASL-CLIF) and North American Consortium for the Study of End-Stage Liver Disease (NACSELD) ACLF definitions have been shown to predict ACLF prognosis. The aim of this study was to compare the ability of the EASL-CLIF versus NACSELD systems over baseline clinical and laboratory parameters in the prediction of in-hospital mortality in admitted patients with decompensated cirrhosis. Five NACSELD centers prospectively collected data to calculate EASL-CLIF and NACSELD-ACLF scores for admitted patients with cirrhosis who were followed for the development of OF, hospital course, and survival. Both the number of OFs and the ACLF grade or presence were used to determine the impact of NACSELD versus EASL-CLIF definitions of ACLF above baseline parameters on in-hospital mortality. A total of 1031 patients with decompensated cirrhosis (age, 57 ± 11 years; male, 66%; Child-Pugh-Turcotte score, 10 ± 2; Model for End-Stage Liver Disease [MELD] score, 20 ± 8) were enrolled. Renal failure prevalence (28% versus 9%, P < 0.001) was more common using the EASL-CLIF versus NACSELD definition, but the prevalence rates for brain, circulatory, and respiratory failures were similar. Baseline parameters including age, white cell count on admission, and MELD score reasonably predicted in-hospital mortality (area under the curve, 0.76). The addition of number of OFs according to either system did not improve the predictive power of the baseline parameters for in-hospital mortality, but the presence of NACSELD-ACLF did. However, neither system was better than baseline parameters in the prediction of 30- or 90-day outcomes. The presence of NACSELD-ACLF is equally effective as the EASL-CLIF ACLF grade, and better than baseline parameters in the prediction of in-hospital mortality in patients with cirrhosis, but not superior in the prediction of longer-term 30- or 90-day outcomes.

Correspondence - Evaluation of a basic point-of-care ultrasound course for residents in internal medicine

Point-of-care ultrasound (POCUS) integrates imaging into the physical examination at the bedside. This offers the advantage of instant clinical information and has shown to speed up the diagnostic process, and to improve diagnostic accuracy and correct treatment.

Focal adhesion kinase inhibition synergizes with nab-paclitaxel to target pancreatic ductal adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) is a very lethal disease, with minimal therapeutic options. Aberrant tyrosine kinase activity influences tumor growth and is regulated by phosphorylation. We investigated phosphorylated kinases as target in PDAC.

Methods

Mass spectrometry-based phosphotyrosine proteomic analysis on PDAC cell lines was used to evaluate active kinases. Pathway analysis and inferred kinase activity analysis was performed to identify novel targets. Subsequently, we investigated targeting of focal adhesion kinase (FAK) in vitro with drug perturbations in combination with chemotherapeutics used against PDAC. Tyrosine phosphoproteomics upon treatment was performed to evaluate signaling. An orthotopic model of PDAC was used to evaluate the combination of defactinib with nab-paclitaxel.

Results

PDAC cell lines portrayed high activity of multiple receptor tyrosine kinases to various degree. The non-receptor kinase, FAK, was identified in all cell lines by our phosphotyrosine proteomic screen and pathway analysis. Targeting of this kinase with defactinib validated reduced phosphorylation profiles. Additionally, FAK inhibition had anti-proliferative and anti-migratory effects. Combination with (nab-)paclitaxel had a synergistic effect on cell proliferation in vitro and reduced tumor growth in vivo.

Conclusions

Our study shows high phosphorylation of several oncogenic receptor tyrosine kinases in PDAC cells and validated FAK inhibition as potential synergistic target with Nab-paclitaxel against this devastating disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01892-z.

[Awake prone positioning in covid-19 patients]

Awake prone positioning in COVID-19 patients with respiratory failure has been applied worldwide. We hypothesize that early intervention of awake prone positioning in this patient category might avoid invasive mechanical ventilation and referral to ICU. We observed approximately 30 patients in Suriname in whom awake prone positioning was applied. Also, we reviewed the existing literature on awake prone positioning and discussion of the advantages and disadvantages of this relatively simple intervention. Prospective studies show an improvement in oxygenation, albeit sometimes temporary, but not a reduction in mortality rate or intubation. Mean duration of symptoms in these studies is 10-11 days. Awake prone positioning in COVID-19 patients with a longer duration of symptoms does not improve survival or need for intubation. No prospective studies on early prone position in COVID-19 patients have been conducted yet.

Cardiac function in relation to myocardial injury in hospitalised patients with COVID-19

BACKGROUND

Previous studies have reported on myocardial injury in patients with coronavirus infectious disease 19 (COVID-19) defined as elevated cardiac biomarkers. Whether elevated biomarkers truly represent myocardial dysfunction is not known. The aim of this study was to explore the incidence of ventricular dysfunction and assess its relationship with biomarker analyses.

METHODS

This cross-sectional study ran from April 1 to May 12, 2020, and consisted of all consecutively admitted patients to the Radboud university medical centre nursing ward for COVID-19. Laboratory assessment included high-sensitivity Troponin T and N‑terminal pro-B-type natriuretic peptide (NT-proBNP). Echocardiographic evaluation focused on left and right ventricular systolic function and global longitudinal strain (GLS).

RESULTS

In total, 51 patients were included, with a median age of 63 years (range 51-68 years) of whom 80% was male. Troponin T was elevated (>14 ng/l) in 47%, and a clinically relevant Troponin T elevation (10 × URL) was found in three patients (6%). NT-proBNP was elevated (>300 pg/ml) in 24 patients (47%), and in four (8%) the NT-proBNP concentration was >1,000 pg/ml. Left ventricular dysfunction (ejection fraction <52% and/or GLS >-18%) was observed in 27%, while right ventricular dysfunction (TAPSE <17 mm and/or RV S' < 10 cm/s) was seen in 10%. There was no association between elevated Troponin T or NT-proBNP and left or right ventricular dysfunction. Patients with confirmed pulmonary embolism had normal right ventricular function.

CONCLUSIONS

In hospitalised patients, it seems that COVID-19 predominantly affects the respiratory system, while cardiac dysfunction occurs less often. Based on a single echocardiographic evaluation, we found no relation between elevated Troponin T or NT-proBNP, and ventricular dysfunction. Echocardiography has limited value in screening for ventricular dysfunction.

Child-Pugh Classification: Time to Abandon?

The Child-Pugh classification is one of the commonest and oldest bedside tools utilized in estimating prognosis in patients with cirrhosis. However, its usage as a risk prediction tool or indeed a decision-making tool should be revisited. In this review, we discuss some inherent issues with the Child-Pugh classification and present a few contexts in which the current usage of Child-Pugh warrants reassessment, elaborating on its utility in acute variceal bleeding, specifically its role in decision-making on early transjugular intrahepatic portosystemic shunt, as well as its use in the context of hepatocellular carcinoma and drug development and dose adjustment.

Graft Dysfunction and Management in Liver Transplantation

Graft dysfunction of the liver allograft manifests across a spectrum in both timing posttransplantation and clinical presentation. This can range from mild transient abnormalities of liver tests to acute liver failure potentially leading to graft failure. The causes of graft dysfunction can be divided into those resulting in early and late graft dysfunction. Although nonspecific, liver biochemistry abnormalities are still the mainstay investigation used in monitoring for dysfunction. This article provides a summary of the main causes and management strategies for liver graft dysfunction in the early through late posttransplant stages.

The impact of obesity in cirrhotic patients with septic shock: A retrospective cohort study

BACKGROUND & AIMS

The prevalence of obesity in cirrhosis is rising. The impact of obesity in critically ill cirrhotic patients with sepsis/septic shock has not been evaluated. This study aimed to examine the relationship between obesity and mortality in cirrhotic patients admitted to the intensive care unit with septic shock.

METHODS

A retrospective cohort study of all cirrhotic patients with septic shock (n = 362) and a recorded body mass index (BMI) from an international, multicentre (CATSS) database (1996-2015) was performed. Patients were classified by BMI as per WHO categories. Primary outcome was in-hospital mortality. Multivariate logistic regression analyses were carried out to determine independent associations with outcome.

RESULTS

In this analysis, mean age was 56.4 years, and 62% were male. Median BMI was 26.3%, and 57.7% were overweight/obese. In-hospital mortality was 71%. Obese patients were more likely to have comorbidities of cardiac disease, lung disease and diabetes. Compared to survivors (n = 105), non-survivors (n = 257) had significantly higher MELD and APACHEII scores and higher requirements for renal replacement therapy and mechanical ventilation (P < .03 for all). Using multivariable logistic regression, increase in BMI (OR 1.07, P = .034), time delay to appropriate antimicrobials (OR 1.16 per hour, P = .003), APACHEII (OR 1.12 per unit, P = .008) and peak lactate (OR 1.15, P = .028) were independently associated with in-hospital mortality.

CONCLUSIONS

Septic shock in cirrhosis carries a high mortality. Increased BMI is common in critically ill cirrhotic patients and independently associated with increased in-hospital mortality.

Management of Cerebral Edema in Acute Liver Failure

Advances in medical care of the acute liver failure patient have led to a significant reduction in mortality related to the condition. Nevertheless, cerebral edema and ensuing brain herniation remains one of the top causes of demise in acute liver failure. Controversy remains regarding the utility of invasive intracranial pressure monitoring as well as usage of novel treatment modalities including therapeutic hypothermia. This review provides a brief summary into the pathophysiology and risk factors for developing cerebral edema in the context of acute liver failure; this review particularly provides a practical focus on general management of the patient with established cerebral edema as well as specific intracranial pressure-lowering strategies.

Intrahepatic vascular changes in non-alcoholic fatty liver disease: Potential role of insulin-resistance and endothelial dysfunction

Metabolic syndrome is a cluster of several clinical conditions characterized by insulin-resistance and high cardiovascular risk. Non-alcoholic fatty liver disease is the liver expression of the metabolic syndrome, and insulin resistance can be a frequent comorbidity in several chronic liver diseases, in particular hepatitis C virus infection and/or cirrhosis. Several studies have demonstrated that insulin action is not only relevant for glucose control, but also for vascular homeostasis. Insulin regulates nitric oxide production, which mediates to a large degree the vasodilating, anti-inflammatory and antithrombotic properties of a healthy endothelium, guaranteeing organ perfusion. The effects of insulin on the liver microvasculature and the effects of IR on sinusoidal endothelial cells have been studied in animal models of non-alcoholic fatty liver disease. The hypotheses derived from these studies and the potential translation of these results into humans are critically discussed in this review.

[Acute respiratory failure caused by minocycline]

BACKGROUND

In the case of pneumonia an infectious cause is always considered first. However, toxic agents and medicines can also be the cause of pneumonia.

CASE DESCRIPTION

A 54-year-old woman was referred to the emergency department because of progressive dyspnoea, a non-productive cough, headache, and fever. She was admitted with the diagnosis community acquired pneumonia. Despite treatment with antibiotics and oxygen she developed hypoxic respiratory failure, which necessitated invasive mechanical ventilation. Imaging diagnostics showed extensive bilateral pulmonary consolidation, despite the absence of a causative agent in cultures. Further medical history-taking revealed that the patient had recently commenced a course of minocycline. She had used this medicine previously and had twice before developed pneumonia without the presence of a proven causative agent. Our differential diagnosis included the toxic effect of minocycline and we treated the patient with methylprednisolone. This resulted in rapid clinical improvement and full recovery of our patient.

CONCLUSION

Acute respiratory failure as a side effect of medication is rare, but nonetheless potentially life-threatening. Despite repeated exposure to minocycline, the link with pneumonia was not previously made in this patient.

Rate-temperature curves as an unambiguous indicator of biological activity in soil

Experiments are described in which we used a mass spectrometer to monitor O(2) uptake of enclosed soil samples as a function of temperature. We found that an Arrhenius plot of the rate of O(2) uptake showed pronounced local maxima attributable to biological activity, whereas similar plots of rates obtained with abiotic soils yielded straight lines. This procedure thus provides a basis for distinguishing biological from chemical activity for reactions, such as O(2) uptake, that can occur via either biological or chemical pathways.

The anti-protozoal drug pentamidine blocks KIR2.x-mediated inward rectifier current by entering the cytoplasmic pore region of the channel

BACKGROUND AND PURPOSE

Pentamidine is a drug used in treatment of protozoal infections. Pentamidine treatment may cause sudden cardiac death by provoking cardiac arrhythmias associated with QTc prolongation and U-wave alterations. This proarrhythmic effect was linked to inhibition of hERG trafficking, but not to acute block of ion channels contributing to the action potential. Because the U-wave has been linked to the cardiac inward rectifier current (I(K1)), we examined the action and mechanism of pentamidine-mediated I(K1) block.

EXPERIMENTAL APPROACH

Patch clamp measurements of I(K1) were made on cultured adult canine ventricular cardiomyocytes, K(IR)2.1-HEK293 cells and K(IR)2.x inside-out patches. Pentamidine binding to cytoplasmic amino acid residues of K(IR)2.1 channels was studied by molecular modelling.

KEY RESULTS

Pentamidine application (24 h) decreased I(K1) in cultured canine cardiomyocytes and K(IR)2.1-HEK293 cells under whole cell clamp conditions. Pentamidine inhibited I(K1) in K(IR)2.1-HEK293 cells 10 min after application. When applied to the cytoplasmic side under inside-out patch clamp conditions, pentamidine block of I(K1) was acute (IC(50)= 0.17 microM). Molecular modelling predicted pentamidine-channel interactions in the cytoplasmic pore region of K(IR)2.1 at amino acids E224, D259 and E299. Mutation of these conserved residues to alanine reduced pentamidine block of I(K1). Block was independent of the presence of spermine. K(IR)2.2, and K(IR)2.3 based I(K1) was also sensitive to pentamidine blockade.

CONCLUSIONS AND IMPLICATIONS

Pentamidine inhibits cardiac I(K1) by interacting with three negatively charged amino acids in the cytoplasmic pore region. Our findings may provide new insights for development of specific I(K1) blocking compounds.

An integrated multi-purpose biology instrument utilizing a single detector, the mass spectrometer

A mass spectrometer is used to analyze the gas phase in a number of reaction vessels filled with Martian soil. By choosing appropriate incubation conditions this instrument can be used to perform a wide spectrum of experiments ranging from the observation of general indices of life, i.e. processes and patterns unexplainable by physico-chemical mechanisms, to assays utilizing isotopes which probe for specific metabolic processes. Of particular interest is the in situ incubation in which a Martian soil sample is maintained at a constant temperature and its gas phase composition analyzed with time. Properly interpreted, this is a very general life-detection probe which makes minimal assumption as to the nature of Martian biology. Other assays and measurements concerning the soil and the atmosphere compatible with this method are also described.

Nitrite and nitrate determinations in plasma: a critical evaluation

Plasma nitrite and nitrate determinations are increasingly being used in clinical chemistry as markers for the activity of nitric oxide synthase and the production of nitric oxide radicals. However, a systematic evaluation of the determination of nitrite and nitrate in plasma has not been performed. In this study the recovery and stability of nitrite and nitrate in whole blood and in plasma, the relation between nitrite and nitrate concentrations in plasma, and possible sources of artifacts were investigated. The main conclusions are: (a) Recovery of nitrite and nitrate from plasma is near-quantitative (87%) and reproducible; (b) nitrite and nitrate are stable in (frozen) plasma for at least 1 year; (c) nitrite in whole blood is very rapidly (> 95% in 1 h) oxidized to nitrate, and therefore plasma nitrite determination alone is meaningless; (d) the ranges of nitrite and nitrate concentrations in plasma samples of 26 healthy persons are 1.3-13 mumol/L (mean 4.2 mumol/L) and 4.0-45.3 mumol/L (mean 19.7 mumol/L), respectively; (e) plasma nitrite and nitrate concentrations were not correlated (nitrite as % of total nitrite + nitrate varied from 3.9% to 88% in plasma samples); and (f) plasma samples should be deproteinized, and background controls for each sample should be included in the assay, to avoid measuring artifactually high nitrite and nitrate concentrations in plasma.

Nitrite and nitrate determinations in plasma: a critical evaluation

Plasma nitrite and nitrate determinations are increasingly being used in clinical chemistry as markers for the activity of nitric oxide synthase and the production of nitric oxide radicals. However, a systematic evaluation of the determination of nitrite and nitrate in plasma has not been performed. In this study the recovery and stability of nitrite and nitrate in whole blood and in plasma, the relation between nitrite and nitrate concentrations in plasma, and possible sources of artifacts were investigated. The main conclusions are: (a) Recovery of nitrite and nitrate from plasma is near-quantitative (87%) and reproducible; (b) nitrite and nitrate are stable in (frozen) plasma for at least 1 year; (c) nitrite in whole blood is very rapidly (&gt; 95% in 1 h) oxidized to nitrate, and therefore plasma nitrite determination alone is meaningless; (d) the ranges of nitrite and nitrate concentrations in plasma samples of 26 healthy persons are 1.3-13 mumol/L (mean 4.2 mumol/L) and 4.0-45.3 mumol/L (mean 19.7 mumol/L), respectively; (e) plasma nitrite and nitrate concentrations were not correlated (nitrite as % of total nitrite + nitrate varied from 3.9% to 88% in plasma samples); and (f) plasma samples should be deproteinized, and background controls for each sample should be included in the assay, to avoid measuring artifactually high nitrite and nitrate concentrations in plasma.

Redox titration of electron acceptor Q and the plastoquinone pool in photosystem II

The primary photochemical quencher Q and the secondary electron acceptor pool in Photosystem II have been titrated. We used particles of Scenedesmus mutant No. 8 that lack System I and allowed the system to equilibrate with external redox mediators in darkness prior to measurement of the fluorescence rise curve. The titration of Q, as indicated by the dark level of Fi, occurs in two discrete steps. The high-potential component (Qh) has a midpoint potential of +68 mV (pH 7.2) and accounts for approximately 67% of Q. The pH sensitivity of the midpoint potential is -60 mV, indicating the involvement of 1 H+/e. The low-potential component (Q1) accounts for the remaining 33% of Q and shows a midpoint potential near--300 mV (pH 7.2). The plastoquinone pool, assayed as the half-time of the fluorescence rise curve, titrates as a single component with a midpoint potential 30--40 mV more oxidizing than that of Qh, i.e., at 106 mV (pH 7.2). The Em shows a pH sensitivity of -60 mV/pH unit, indicating the involvement of 1 H+/e. The observation that all 12--14 electron equivalents in the pool titrate as a single component indicates that the heterogeneity otherwise observed in the secondary acceptor system is a kinetic rather than a thermodynamic property. Illumination causes peculiar, and as yet unclarified, changes of both Q and the secondary pool under anaerobic conditions that are reversed by oxygen.

Evidence that the intermediate electron acceptor, A2, in photosystem I is a bound iron-sulfur protein

Absorption changes accompanying the formation of light-induced P-700+ were investigated in a highly enriched Photosystem I preparation where an intermediate electron acceptor preceding P-430 could be detected. In an enriched Photosystem I particle, light-induced reversible absorption changes observed at 700 nm in the presence of dithionite resembled those previously seen at 703 nm and 820 nm [9], thus indicating the presence of a backreaction between P700+ and A-2. After this same Photosystem I particle was treated to denature the bound iron-sulfur centers, the photochemical changes that could be attributed to P-700 in equilibrium A2 were completely lost. These results provide evidence that the intermediate electron acceptor, A2, is a bound iron-sulfur protein. Additional studies in the 400--500 nm region with Photosystem I particles prepared by sonication indicate that the spectrum of A2 is different from that of P-430.

Comparison of photosynthetic activities of spinach chloroplasts with those of corn mesophyll and corn bundle sheath tissue

Bundle sheath and mesophyll chloroplasts from Zea mays showed comparable rates of O(2) evolution, which amounted to about half of the rate observed in spinach (Spinacia oleracea) chloroplasts.Ratios of 4.5, 4.6, and 6.2 Mn(2+) atoms per 400 chlorophylls were observed in mesophyll, bundle sheath, and spinach chloroplasts, respectively. These ratios roughly correspond to the observed O(2) evolution rates.Rates of electron transport from water to methylviologen (photosystem I and II) in both types of corn chloroplasts were about one-third that in spinach. Compared to spinach, transport rates from reduced diaminodurene to methylviologen (photosystem I) were about one-third and greater than one-half in mesophyll and bundle sheath material, respectively.In both types of corn chloroplasts, electron flow from photosystem II to P700 was abnormal. This observation, together with the low rates of all activities, suggests that damage occurred during isolation. Such damage may limit the quantitative significance of observations made with these materials (including the following data).Measurements of flash yields of O(2) evolution or O(2) uptake showed that the size of the photosynthetic unit was the same in photosystems I and II and in all three types of chloroplasts (about 400 chlorophylls per equivalent).Similarity of the photochemical cross-section of the two photosystems in the three preparations was also found in optical experiments: that is the half-times of the fluorescence rise in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) (photosystem II) and of the photooxidation of P700 (photosystem I).The ratio of P700 to chlorophyll appeared to be about 2-fold higher in bundle sheath chloroplasts than in the other materials (1/200 versus 1/400).

Kinetics and Apparent K(m) of Oxygen Cycle under Conditions of Limiting Carbon Dioxide Fixation

A mass spectrometer with a membrane inlet was used to monitor light-driven O(2) evolution, O(2) uptake, and CO(2) uptake in suspensions of algae (Scenedesmus obliquus). We observed the following. (a) The rate of O(2) uptake, which, in the presence of iodoacetamide, replaces the uptake of CO(2), showed a distinct plateau (V(max)) beyond approximately 30% O(2) and was half-maximal at approximately 8% O(2). We concluded that this light-driven O(2) uptake process, which does not involve carbon compounds, is saturated at lower O(2) concentrations than are photorespiration and glycolate formation. (b) In the absence of inhibitor, O(2) evolution was relatively unaffected by the presence or absence of CO(2). During the course of CO(2) depletion, electron flow to CO(2) was replaced by an equivalent flow to O(2). (c) There was a distinct delay between the cessation of CO(2) uptake and the increase in O(2) uptake. We ascribe this delay to the transient utilization of another electron acceptor-possibly bicarbonate or another bound form of CO(2).

Photosynthetic oxygen evolution from hydrogen peroxide

A study was made of the interactions of flash-illuminated chloroplasts with hydrogen peroxide. We conclude: 1. The oxygen precursor system can be reduced beyond the S0 state to an S-1 state, which can be oxidized to S0 by a single flash. 2. In the dark, a two-electron donation by H2O2 takes place which reduces S2 to S0 and S1 to S-1. 3. At the same time, two-electron oxidations by H2O2 re-form, S2 from S0 and S1 from S-1. 4. The catalase-like activity due to this cyclic oxidation and reduction of the S enzyme is higher with the S2 in equilibrium S0 couple than with the S1 in equilibrium S-1 couple. Another process, however, is responsible for most of the O2 evolution from H2O2 in the light. Our evidence indicates that this process: (1) is independent of the S states and insensitive to Tris washing, (2) turns over rapidly in high concentrations of peroxide, (3) yields 1 O2 per electron passing through system II; (4) dismutates two H2O2 molecules, so that there is no net consumption of 'holes'.

Plastocyanin as the possible site of photosynthetic electron transport inhibition by glutaraldehyde

Treatment of spinach chloroplasts with glutaraldehyde causes an inhibition in the electron transport chain between the two photosystems. Measurements of O(2) flash yields, pH exchange, and fluorescence induction show that the O(2) evolving apparatus, photosystem II and its electron acceptor pool are not affected. The behavior of P700 indicates that its reduction but not its oxidation, is severely inhibited. Cytochrome f is still reducible by photosystem II but also slowly oxidizable by photosystem I. The sensitivity of isolated plastocyanin to glutaraldehyde further supports the conclusion that glutaraldehyde inhibits at the plastocyanin level and thereby induces a break between P700 and cytochrome f.

Stabilization by glutaraldehyde of high-rate electron transport in isolated chloroplasts

Treatment of isolated chloroplasts with glutaraldehyde affects their ability to photoreduce artificial electron acceptors. The remaining rate of O2 evolution approaches zero with methyl viologen, is low with ferricyanide, but nearly normal with lipophilic Photosystem II acceptors, like oxidized p-phenylenediamine and oxidized diaminodurene. Since Photosystem I donor reactions are also affected, a specific site of inhibition of electron transport to Photosystem I is indicated. At the same time, glutaraldehyde prolongs the longevity of the chloroplasts stored in dark. In control samples the half-life of Photosystem II activity varied between 5 days at 4degreesC and 1 day at 25degreesC. Glutaraldehyde treatment increased these half times approx. 3-fold. The glutaraldehyde doses required to induce inhibition and stabilization were very similar.

Photoreduction of O(2) Primes and Replaces CO(2) Assimilation

A mass spectrometer with a membrane inlet system was used to monitor directly gaseous components in a suspension of algae. Using labeled oxygen, we observed that during the first 20 seconds of illumination after a dark period, when no net O(2) evolution or CO(2) uptake was observed, O(2) evolution was normal but completely compensated by O(2) uptake. Similarly, when CO(2) uptake was totally or partially inhibited, O(2) evolution proceeded at a high (near maximal) rate. Under all conditions, O(2) uptake balanced that fraction of the O(2) evolution which could not be accounted for by CO(2) uptake.From these observations we concluded that O(2) and CO(2) are in direct competition for photosynthetically generated reducing power, with O(2) being the main electron acceptor during the induction process and under other conditions in which CO(2) reduction cannot keep pace with O(2) evolution. The high rate of the O(2) uptake reaction observed in the presence of iodoacetamide, KCN, or carbonyl cyanide p-trifluoromethyoxyphenylhydrazone, suggests that a special high capacity oxidase distinct from ribulose diphosphate oxygenase exists in whole cells. The rapid reduction of molecular O(2) after a period of darkness probably serves as a priming reaction for the photosynthetic apparatus. The high steady state rate of the O(2) cycle in the absence of CO(2) fixation suggests that the regulation of photosynthesis does not involve significant changes in the rate of photochemical electron transport.

Determination of H+/e- ratios in chloroplasts with flashing light

Using a rapid pH electrode, measurements were made of the flash-induced proton transport in isolated spinach chloroplasts. To calibrate the system, we assumed that in the presence of ferricyanide and in steady-state flashing light, each flash liberates from water one proton per reaction chain. We concluded that with both ferricyanide and methylviologen as acceptors two protons per electron are translocated by the electron transport chain connecting Photosystem II and I. With methyl viologen but not with ferricyanide as an acceptor, two additional protons per electron are taken up due to Photosystem I activity. One of these latter protons is translocated to the inside of the thylakoid while the other is taken up in H2O2 formation. Assuming that the proton released during water splitting remains inside the thylakoid, we compute H+/e- ratios of 3 and 4 for ferricyanide and methylviologen, respectively. In continuous light of low intensity, we obtained the same H+/e- ratios. However, with higher intensities where electron transport becomes rate limited by the internal pH, the H+/e- ratio approached 2 as a limit for both acceptors. A working model is presented which includes two sites of proton translocation, one between the photoacts, the other connected to Photosystem I, each of which translocates two protons per electron. Each site presents a approximately 30 ms diffusion barrier to proton passage which can be lowered by uncouplers to 6-10 ms.

Photon trapping in photosystem II of photosynthesis. The fluorescence rise curve in the presence of 3-(3,4-dichlorophenyl)-1,1-dimetnhylurea

Using isolated chloroplasts in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an analysis was made of the rise of the fluorescence yield effected by weak light. Depending on the pretreatment, the time-course of the rapid photochemical part of the rise varied between nearly first-order and quadratic kinetics, i.e., reflected either a one-quantum or a two-quantum conversion. We consider the occurrence of two photoreductants per system II unit, which are reoxidized in different dark reactions. The data further showed that the "first-order process" is also inhomogeneous.