Reversibility of alexithymia with effective treatment of moderate-to-severe psoriasis: longitudinal data from EPIDEPSO.

BACKGROUND: Alexithymia refers to difficulty in identifying and expressing emotions. Alexithymia is associated with high burden of disease in patients with psoriasis. OBJECTIVES: To investigate whether alexithymia was reversible in patients with psoriasis following real-life therapeutic intervention. METHODS: The Epidemiological Study in Patients with Recently Diagnosed Psoriasis (EPIDEPSO; NCT01964443) was a 1-year multicentre observational study investigating the prevalence of alexithymia and other psychosocial comorbidities in patients with psoriasis with ≤ 10 years' disease duration and eligible for systemic treatment. Alexithymia was assessed using the Toronto Alexithymia Scale (TAS-20) at baseline, 6 months and 1 year. RESULTS: There was a statistically significant decrease in the prevalence of alexithymia in the follow-up cohort, from 26·7% at baseline to 21·2% at 6 months and 18·8% at 1 year. More than half of the patients (n = 77, 53·8%) who were alexithymic at baseline experienced reversion of their alexithymia. Reversion of alexithymia was higher in patients who reached a high level of disease control, defined as ≥ 75% or ≥ 90% improvement in Psoriasis Area and Severity Index. Reversion of alexithymia was associated with dramatic improvement in quality of life, anxiety and depression. Moreover, hazardous alcohol use, highly prevalent in patients with alexithymia, was reduced almost threefold at 1 year. CONCLUSIONS: Alexithymia and associated high disease burden may be reversible in patients with effective treatment of psoriasis. Proactive recognition of patients who are unable to identify and express their feelings is important.

Prevalence of alexithymia in patients with psoriasis and its association with disease burden: a multicentre observational study.

BACKGROUND: Single-centre studies show that alexithymia, defined as difficulty in recognizing and describing emotions, is more prevalent among patients with psoriasis than in the general population. However, its prevalence and the consequences of the association between alexithymia and psoriasis are unclear. OBJECTIVES: The primary objective of this study was to determine the prevalence of alexithymia, as defined by a score ≥ 61 in the 20-item Toronto Alexithymia Scale, in a large sample of patients who had plaque psoriasis for ≤ 10 years and were eligible for phototherapy or systemic treatment. The secondary objectives were to investigate the relationship between alexithymia and the clinical and psychological aspects of psoriasis. METHODS: Data were collected in the framework of an observational, multicentre, international study, the EPidemiological Study In Patients With Recently DiagnosEd PSOriasis (EPIDEPSO), aiming at investigating the prevalence of alexithymia and other psychosocial comorbidities in patients with psoriasis of ≤ 10 years' disease duration. RESULTS: The prevalence of alexithymia within a cohort of 670 patients was 24·8% (95% confidence interval 21·7-28·2). Patients with alexithymia had a higher burden of psoriasis, including significant impairment of quality of life, higher levels of anxiety and depression, a higher risk of alcohol dependency and impairment of work productivity, compared with patients without alexithymia. CONCLUSIONS: It is important to identify alexithymic patients with psoriasis in clinical practice as they experience a higher disease burden and have a lower ability to express their feelings.

Engineering the internal cavity of neuroglobin demonstrates the role of the haem-sliding mechanism.

Neuroglobin is a member of the globin family involved in neuroprotection; it is primarily expressed in the brain and retina of vertebrates. Neuroglobin belongs to the heterogeneous group of hexacoordinate globins that have evolved in animals, plants and bacteria, endowed with the capability of reversible intramolecular coordination, allowing the binding of small gaseous ligands (O2, NO and CO). In a unique fashion among haemoproteins, ligand-binding events in neuroglobin are dependent on the sliding of the haem itself within a preformed internal cavity, as revealed by the crystal structure of its CO-bound derivative. Point mutants of the neuroglobin internal cavity have been engineered and their functional and structural characterization shows that hindering the haem displacement leads to a decrease in CO affinity, whereas reducing the cavity volume without interfering with haem sliding has negligible functional effects.

One-year safety and efficacy of ustekinumab and results of dose adjustment after switching from inadequate methotrexate treatment: the TRANSIT randomized trial in moderate-to-severe plaque psoriasis.

BACKGROUND: There are limited long-term, 'real-world' data on ustekinumab, or the effect of dose adjustment in suboptimal responders. OBJECTIVES: We describe 52-week data from TRANSIT, which initiated ustekinumab by licensed regimen and investigated exploratory dose adjustment. METHODS: Patients with moderate-to-severe psoriasis and inadequate methotrexate response received ustekinumab, with immediate or gradual methotrexate withdrawal. Outcomes were similar between treatment arms at week 12 (primary endpoint), so week 52 data were pooled. Patients weighing ≤ 100 kg or > 100 kg were administered ustekinumab 45 or 90 mg, respectively. Patients weighing ≤ 100 kg without 75% improvement in Psoriasis Area and Severity Index (PASI 75) response at weeks 28 or 40 received a dose adjustment to 90 mg. The primary analysis used observed data. RESULTS: Overall, 391 and 98 patients received ustekinumab 45 and 90 mg, respectively. Forty-four patients (9%) discontinued before week 52 (0·4% due to adverse events). At week 52 (in the overall population), 369 patients (83%) achieved a PASI score ≤ 5, and 341 patients (77%) achieved PASI 75; the median PASI score decreased from 15 at baseline to 1·8. At weeks 28 and 40, 84 and 31 patients, respectively, did not achieve PASI 75 and received a dose adjustment; by week 52, 35/82 (43%) and 15/31 (48%) of these patients, respectively, achieved PASI 75 (two discontinued between weeks 28 and 40). CONCLUSIONS: Ustekinumab showed sustained 1-year efficacy and was well tolerated when initially administered according to label. Adjusting the ustekinumab dose to 90 mg may result in clinically meaningful improvement in response in patients weighing ≤ 100 kg with suboptimal initial response.

Efficacy and tolerability of bendamustine, bortezomib and dexamethasone in patients with relapsed-refractory multiple myeloma: a phase II study.

Bendamustine demonstrated synergistic efficacy with bortezomib against multiple myeloma (MM) cells in vitro and seems an effective treatment for relapsed-refractory MM (rrMM). This phase II study evaluated bendamustine plus bortezomib and dexamethasone (BVD) administered over six 28-day cycles and then every 56 days for six further cycles in patients with rrMM treated with 4 prior therapies and not refractory to bortezomib. The primary study end point was the overall response rate after four cycles. In total, 75 patients were enrolled, of median age 68 years. All patients had received targeted agents, 83% had 1-2 prior therapies and 33% were refractory to the last treatment. The response ratepartial response (PR) was 71.5% (16% complete response, 18.5% very good PR, 37% partial remission). At 12 months of follow-up, median time-to-progression (TTP) was 16.5 months and 1-year overall survival was 78%. According to Cox regression analysis, only prior therapy with bortezomib plus lenalidomide significantly reduced TTP (9 vs 17 months; hazard ratio=4.5; P=0.005). The main severe side effects were thrombocytopenia (30.5%), neutropenia (18.5%), infections (12%), neuropathy (8%) and gastrointestinal and cardiovascular events (both 6.5%). The BVD regimen is feasible, effective and well-tolerated in difficult-to-treat patients with rrMM.

Switching between the alternative structures and functions of a 2-Cys peroxiredoxin, by site-directed mutagenesis.

Members of the typical 2-Cys peroxiredoxin (Prx) subfamily represent an intriguing example of protein moonlighting behavior since this enzyme shifts function: indeed, upon chemical stimuli, such as oxidative stress, Prx undergoes a switch from peroxidase to molecular chaperone, associated to a change in quaternary structure from dimers/decamers to higher-molecular-weight (HMW) species. In order to detail the structural mechanism of this switch at molecular level, we have designed and expressed mutants of peroxiredoxin I from Schistosoma mansoni (SmPrxI) with constitutive HMW assembly and molecular chaperone activity. By a combination of X-ray crystallography, transmission electron microscopy and functional experiments, we defined the structural events responsible for the moonlighting behavior of 2-Cys Prx and we demonstrated that acidification is coupled to local structural variations localized at the active site and a change in oligomerization to HMW forms, similar to those induced by oxidative stress. Moreover, we suggest that the binding site of the unfolded polypeptide is at least in part contributed by the hydrophobic surface exposed by the unfolding of the active site. We also find an inverse correlation between the extent of ring stacking and molecular chaperone activity that is explained assuming that the binding occurs at the extremities of the nanotube, and the longer the nanotube is, the lesser the ratio binding sites/molecular mass is.

Structural dynamics of myoglobin.

Protein structure is endowed with a complex dynamic nature, which rules function and controls activity. The experimental investigations that yield information on protein dynamics are carried out in solution; however, in most cases, the determination of protein structure is carried out by crystallography that relies on the diffraction properties of a large number of molecules, in approximately the same conformation, arranged in a three-dimensional lattice. Myoglobin, maybe the most thoroughly characterized protein, has allowed the formulation of general principles in the field of protein structure-function correlation and, since the late 1990s, it has been possible to obtain directly some insight into the complex dynamic behavior of myoglobin and other proteins by Laue diffraction. This chapter describes some of the technological features involved in obtaining reliable data by time-resolved Laue crystallography, with subnanosecond time resolution. A synopsis of the more significant findings obtained by laser photolysis of myoglobin-CO crystals is also presented, emphasizing the more general aspects of dynamics relevant to the complex energy landscape of a protein.

[Pulmonary physiopathology in scleroderma: study of respiratory function in 86 patients]. / La fisiopatologia polmonare nella sclerodermia: esame della funzionalità respiratoria in 86 pazienti.

OBJECTIVE: To contribute to an early diagnosis of pulmonary involvement in scleroderma by evaluating the correlation between respiratory symptoms and functional respiratory data observed. PATIENTS AND METHODS: 86 patients affected by scleroderma, 76 women and 10 men, age 14-75, underwent lung function tests, blood gas sample, CO diffusing capacity in setting and supine position, respiratory drive measurement through P0.1 and evaluation of the respiratory muscles efficiency with Maximum Inspiratory Pressure (MIP). RESULTS: Data obtained suggested us to divide our patients in four different groups: first group where both spirometric data and pulmonary diffusion were normal; a second group with a clear reduction of pulmonary diffusion likely due to the reduction of vascular bed; a third group where we observed a restrictive ventilatory impairment due to the reduction of the compliance and a reduction of the pulmonary diffusion likely related to interstitial damage; finally, a fourth group where beside a restricted spirometric outline we have detected a more accentuated reduction of pulmonary diffusion likely due to pulmonary hypertension. Moreover, our study has highlighted a progressive decrease of MIP and Maximum Voluntary Ventilation (MVV) shifting from the first to the fourth group, suggesting reduction of the muscular efficiency with an increase of P0.1 index of activity in the respiratory drive. CONCLUSIONS: The results could explain the dyspnea often reported by the patients affected by scleroderma even without spirometric alteration.

[Possible effects of non invasive mechanical ventilation on respiratory drive and muscles]. / Possibili effetti della ventilazione meccanica non invasiva su drive e muscolatura respiratoria.

OBJECTIVE: To evaluate whether long-term Non-Invasive Mechanical Ventilation (NIMV) might have an effect on respiratory drive and respiratory muscles strength, measuring mouth occlusion pressure (P0,) and maximal inspiratory pressure (MIP). PATIENTS AND METHODS: 20 consecutive patients with hypercapnic respiratory failure underwent measurements of dyspnea, respiratory drive and respiratory muscles strength before hospital treatment with NIMV; those patients who showed significant improvement of gas-exchange continued home ventilation for a period of four weeks, and were readmitted to hospital for re-evaluation of Borg's scale for dyspnea, P0,1 and MIP. RESULTS: Data obtained show a mild reduction of P0,1 and a significant improvement of respiratory muscles strength, with satisfactory dyspnea relief. CONCLUSIONS: We conclude that unloading respiratory muscles through mechanical ventilation results in better muscle performance in the long-term that could act, together with normalization of gas-exchange, on neuromuscular respiratory drive and contribute to dyspnea relief.

The anti-schistosomal drug praziquantel is an adenosine antagonist.

The mechanism of action of praziquantel (PZQ), the drug of choice against schistosomiasis, is still unclear. Since exposure of schistosomes to the drug is associated with calcium influx and muscular contraction, calcium channels have been suggested as the target, although direct combination of PZQ with their subunits was never demonstrated. We report a hitherto unknown effect of PZQ, namely the inhibition of nucleoside uptake, as observed in living worms using radio-isotope labelled adenosine and uridine. This effect is clearly seen in schistosomes but is absent in mammalian cells in culture. Moreover it is a specific pharmacological effect seen exclusively with the active levo-R(-)stereo isomer of the drug, and is shared by at least one benzodiazepine having antischistosomal activity. This novel effect acquires significance given that schistosomes cannot synthesize purine nucleosides de novo. A possible relationship between this novel effect and the known action of PZQ on calcium channels is discussed, since adenosine is known to bind to specific receptors and to behave as an indirect antagonist of calcium release in mammalian cells. If calcium channels were correlated with adenosine receptors also in schistosomes, as they are in mammals, this would support the hypothesis that PZQ-induced calcium influx may be correlated to adenosine receptor blockade.

Neuroglobin, seven years after.

Neuroglobin is expressed in vertebrates brain and belongs to a branch of the globin family that diverged early in evolution. Sequence conservation suggests a relevant role in the nervous system, with tight structural restraints. Experiments in vivo and in vitro showed increased hypoxic stress damage upon repressing neuroglobin biosynthesis and improved recovery following overexpression. Neuroglobin shows internal heme hexacoordination, which controls oxygen affinity and kinetics. Neuroglobin concentration, oxygen affinity and enhanced autooxidation question a role in oxygen delivery; thus it was proposed that the neuroprotective effect might be due to radical scavenging or activation of protection mechanisms. Neuroglobin's structure shows a peculiar internal cavity of very large size. Binding of heme ligands is associated to a conformational change involving the heme that "slides" into the pre-existing cavity and makes the sixth coordination position available. These features may pave the way to an understanding of neuroprotection by neuroglobin.

A globin for the brain.

The discovery that a myoglobin-like hemeprotein (called neuroglobin) is expressed in our brain raised considerable curiosity from the standpoints of biochemistry and pathophysiology alike. Neuroglobin is involved in neuroprotection from damage due to hypoxia or ischemia in vitro and in vivo; overexpression of neuroglobin ameliorates the recovery from stroke in experimental animals. The mechanism underlying this remarkable effect is still mysterious. Structural studies revealed that neuroglobin has a typical globin fold, and despite being hexacoordinated, it binds reversibly O2, CO, and NO, undergoing a substantial conformational change of the heme and of the protein. The possible mechanisms involved in neuroprotection are briefly reviewed. Neuroglobin is unlikely to be involved in O2 transport (like myoglobin), although it seems to act as a sensor of the O2/NO ratio in the cell, possibly regulating the GDP/GTP exchange rate forming a specific complex with the G(alpha beta gamma)-protein when oxidized but not when bound to a gaseous ligand. Thus it appears that neuroglobin is a stress-responsive sensor for signal transduction in the brain, mediated by a ligand-linked conformational change of the protein.

Consolidation therapy for adult acute myeloid leukemia: a systematic analysis according to evidence based medicine.

Post-remission therapy in acute myeloid leukemia (AML) remains problematic. It has been demonstrated that younger patients can maintain longer complete remissions (CR) with aggressive post-remission therapies after induction treatment: allogeneic (allo), autologous (auto) stem cell transplantation (SCT), or intensive chemotherapy (ICC). The purpose of our study was to identify the most important randomized and controlled studies comparing these three therapeutic options, in order to draw conclusions and possible suggestions for post-remission therapy of AML, according to the evidence based medicine (EBM) rules. We performed an exhaustive analysis of the literature, searching either in electronic databases or among the references of the identified articles (hand searching). We searched the MEDLINE computer database for reports from 1985 through January 2005 and selected for analysis the clinical trials conducted over adults affected by newly diagnosed AML aged less than 65 years. The study design had to satisfy strict methodological criteria and must consider global mortality and/or disease free survival as primary outcomes. Overall we found 7750 papers; by using the limits "clinical trial" as publication type, "all adults 19+ years", we were able to select 344 papers. Among these, a further selection was made, based on two main clinical queries: 1) is auto-SCT superior to ICC/no other therapy in improving DFS and/or OS in adult AML patients in first CR? 2) is allo-SCT superior to auto-SCT/other therapeutic options in improving DFS and/or OS in adult AML patients in first CR? Concerning the first query, a possible advantage of auto-SCT over ICC was not clearly supported by data from clinical trials; there is no evidence that auto-SCT is superior in terms of OS to chemotherapy. Nevertheless, the reported TRM has been significantly reduced within the past years. Thus, the percentage of patients suitable for auto-SCT in CR has increased. Moreover, the scarce data concerning the comparison between auto-SCT and chemotherapy in different subsets of patients are unable to suggest a differentiated approach in patients with high-risk, standard-risk or low-risk AML. Data from the literature show that patients with unfavorable risk disease are more often addressed to allo-SCT and patients with low-risk disease receive more often intensive consolidation chemotherapy. Concerning the second query, interpretation of data from the main prospective studies about the role of allo-SCT in previously untreated AML is not easy. The first problem is the lack of real randomized clinical trials; in fact, according to the reported studies, AML patients generally receive allo-SCT on the basis of donor availability (the so called "genetic randomization"). The second problem is the frequent absence of intention to treat analysis. Despite methodological limitations, it was possible to compare allo-SCT with auto-SCT on a donor versus no-donor analysis and within risk groups. No overall benefit of allo-grafting on survival was demonstrated by any trial. In conclusion, the EBM approach highlighted the limitations observed in the published studies concerning consolidation therapy in AML; some suggestions, emerging from non-randomized, as well as randomized studies, are adequate, but not conclusive. This point, coupled with the intrinsic complexity to study AML biological heterogeneity, is probably a major obstacle to draw conclusive evidences for consolidation therapy in AML. These observations should plan to address new randomized studies on AML therapy; however, due to the emergence of genetic subgroups and new drugs targeting specific abnormalities, these trials should probably be designed directly focusing on the single entities. In this way, the cure of AML could eventually become the cure of each specific AML subset with its peculiar biological, molecular and prognostic features.

N-oxide sensing and denitrification: the DNR transcription factors.

All denitrifiers can keep the steady-state concentrations of nitrite and nitric oxide (NO) below cytotoxic levels by controlling the expression of denitrification gene clusters by redox signalling through transcriptional regulators belonging to the CRP (cAMP receptor protein)/FNR (fumarate and nitrate reductase regulator) superfamily.

TRF2 inhibition promotes anchorage-independent growth of telomerase-positive human fibroblasts.

Although telomere instability is observed in human tumors and is associated with the development of cancers in mice, it has yet to be established that it can contribute to the malignant transformation of human cells. We show here that in checkpoint-compromised telomerase-positive human fibroblasts an episode of TRF2 inhibition promotes heritable changes that increase the ability to grow in soft agar, but not tumor growth in nude mice. This transforming activity is associated to a burst of telomere instability but is independent of an altered control of telomere length. Moreover, it cannot be recapitulated by an increase in chromosome breaks induced by an exposure to gamma-radiations. Since it can be revealed in the context of telomerase-proficient human cells, telomere dysfunction might contribute to cancer progression even at late stages of the oncogenesis process, after the telomerase reactivation step.

Upfront high-dose sequential therapy (HDS) versus VACOP-B with or without HDS in aggressive non-Hodgkin's lymphoma: long-term results by the NHLCSG.

BACKGROUND: There is not univocal concordance for using high-dose sequential therapy (HDS) as first-line treatment for aggressive non-Hodgkin's lymphoma (NHL). We designed this study to evaluate the usefulness of HDS followed by high-dose therapy (HDT) with autologous stem cell transplantation as front-line treatment in different subsets of aggressive NHL. PATIENTS AND METHODS: Among 223 patients aged 15-60 years with aggressive, advanced stage NHL, 106 patients were randomized to VACOP-B (etoposide, doxorubicin, cyclophosphamide, vincristine, prednisone, bleomycin) for 12 weeks (plus HDS/HDT in case of persistent disease) (arm A), and 117 patients to VACOP-B for 8 weeks plus upfront HDS/HDT (arm B). RESULTS: According to the intention-to-treat analysis, the complete response rate was 75% for arm A and 72.6% for arm B. With a median follow-up of 62 months there was no difference in 7-year probability of survival (60% and 57.8%; P = 0.5), disease-free survival (DFS) (62% and 71%; P = 0.2) and progression-free survival (PFS) (44.9% and 40.9%; P = 0.7) between the two arms. Subgroup analyses confirmed that the best results in terms of survival, DFS and PFS were achieved by patients with large B-cell NHL without bone marrow (BM) involvement, independently of the treatment arm. Results were poorer in other categories of patients and poorest in patients with BM involvement. CONCLUSIONS: Aggressive NHL patients do not benefit from upfront HDS/HDT.

N-oxide sensing in Pseudomonas aeruginosa: expression and preliminary characterization of DNR, an FNR-CRP type transcriptional regulator.

In denitrifying bacteria, the concentration of NO is maintained low by a tight control of the expression and activity of nitrite and NO reductases. Regulation involves redox-linked transcription factors, such as those belonging to the CRP-FNR (cAMP receptor protein-fumarate and nitrate reductase regulator) superfamily, which act as oxygen and N-oxide sensors. Given that few members of this superfamily have been characterized in detail, we have cloned, expressed and purified the dissimilative nitrate respiration regulator from Pseudomonas aeruginosa. To gain insights on the structural properties of the dissimilative nitrate respiration regulator, we have also determined the aggregation state of the purified protein and its ability to bind hydrophobic compounds such as 8-anilino-1-naphthalenesulphonic acid.

The structural dynamics of myoglobin.

Conformational fluctuations in proteins were initially invoked to explain the observation that diffusion of small ligands through the matrix is a global phenomenon. Small globular proteins contain internal cavities that play a role not only in matrix dynamics but also in controlling function, tracing a pathway for the diffusion of the ligand to and from the active site. This is the main point addressed in this Review, which presents pertinent information obtained on myoglobin (Mb). Mb, a simple globular heme protein which binds reversibly oxygen and other ligands. The bond between the heme Fe(II) and gaseous ligands can be photodissociated by a laser pulse, generating a non-equilibrium population of protein structures that relaxes on a picosecond to millisecond time range. This process is associated with migration of the ligand to internal cavities of the protein, which are known to bind xenon. Some of the results obtained by laser photolysis, molecular dynamics simulations, and X-ray diffraction of intermediate states of wild-type and mutant myoglobins are summarized. The extended relaxation of the globin moiety directly observed by Laue crystallography reflects re-equilibration among conformational substates known to play an essential role in controlling protein function.

Trichomonas vaginalis degrades nitric oxide and expresses a flavorubredoxin-like protein: a new pathogenic mechanism?

Besides possessing many physiological roles, nitric oxide (NO) produced by the immune system in infectious diseases has antimicrobial effects. Trichomoniasis, the most widespread non-viral sexually transmitted disease caused by the microaerophilic protist Trichomonas vaginalis, often evolves into a chronic infection, with the parasite able to survive in the microaerobic, NO-enriched vaginal environment. We relate this property to the finding that T. vaginalis degrades NO under anaerobic conditions, as assessed amperometrically. This activity, which is maximal (133 +/- 41 nmol NO/10(8) cells per minute at 20 degrees C) at low NO concentrations (< or = 1.2 microM), was found to be: (i) NADH dependent, (ii) cyanide insensitive and (iii) inhibited by O(2). These features are consistent with those of the Escherichia coli A-type flavoprotein (ATF), recently discovered to be endowed with NO reductase activity. Using antibodies against the ATF from E. coli, a protein band was immunodetected in the parasite grown in a standard medium. If confirmed, the expression of an ATF in eukaryotes suggests that the genes coding for ATFs were transferred during evolution from anaerobic Prokarya to pathogenic protists, to increase their fitness for the microaerobic, parasitic life style. Thus the demonstration of an ATF in T. vaginalis would appear relevant to both pathology and evolutionary biology. Interestingly, genomic analysis has recently demonstrated that Giardia intestinalis and other pathogenic protists have genes coding for ATFs.

Control of respiration by nitric oxide in Keilin-Hartree particles, mitochondria and SH-SY5Y neuroblastoma cells.

The pattern of cytochrome c oxidase inhibition by nitric oxide (NO) was investigated polarographically using Keilin-Hartree particles, mitochondria and human neuroblastoma cells. NO reacts with purified cytochrome c oxidase forming either a nitrosyl- or a nitrite-inhibited derivative, displaying distinct kinetics and light sensitivity of respiration recovery in the absence of free NO. Keilin-Hartree particles or cells, respiring either on endogenous substrates alone or in the presence of ascorbate, as well as state 3 and state 4 mitochondria respiring on glutamate and malate, displayed the rapid recovery characteristic of the nitrite derivative. All systems, when respiring in the presence of tetramethyl-p-phenylenediamine, were characterised by the slower, light-sensitive recovery typical of the nitrosyl derivative. Together the results suggest that the reaction of NO with cytochrome c oxidase in situ follows two alternative inhibition pathways, depending on the electron flux through the respiratory chain.