Investigating the relationship between Epstein-Barr virus infection and gastric cancer: A systematic review and meta-analysis.

Background and Aims: Gastric cancer (GC) is a common cancer type worldwide, and various factors can be involved in its occurrence. One of these factors is Epstein-Barr virus (EBV) infection. In this regard, a systematic review and meta-analysis was conducted to achieve a better understanding of the EBV prevalence in GC samples. Methods: English databases were searched and studies that reported the prevalence and etiological factors of EBV related to GC from July 2007 to November 2022 were retrieved. The reported data were selected based on the inclusion and exclusion criteria. The pooled prevalence of EBV infection with 95% confidence intervals was calculated. Quality assessment, heterogeneity testing, and publication bias assessment were also performed. The literature search showed 953 studies, of which 87 studies met our inclusion criteria and were used for meta-analysis. Results: The pooled prevalence of EBV infection related to GC was estimated to be 9.5% (95% confidence interval [CI]: 8.2%-11%) in the general population. The prevalence of EBV infection related to GC by gender was 13.5% (95% CI: 11.1%-16.3%) in males and 7.6% (95% CI: 5.4%-10.6%) in females. No significant differences were observed in terms of geographical region. Out of the 87 studies included in the meta-analysis, the most common diagnostic test was in situ hybridization (58 cases). Conclusions: Altogether, the results indicated that EBV infection is one of the important factors in the development of GC. However, this does not necessarily mean that EBV infection directly causes GC since other factors may also be involved in the development of GC. Therefore, it is recommended to conduct extensive epidemiological studies on various aspects of the relationship between this virus and GC, which can provide valuable information for understanding the relationship between EBV and GC.

Discovery of novel inhibitors for Pseudomonas aeruginosa lipase enzyme from in silico and in vitro studies.

Pseudomonas aeruginosa is an opportunistic pathogen prone to developing drug-resistance and is a major cause of infection for burn patients and patients suffering from cystic fibrosis or are hospitalized in intensive care units. One of the virulence factors of this bacterium is the lipase enzyme that degrades the extracellular matrix of the host tissue and promotes invasion. Bromhexine is a mucolytic drug and has recently been reported to function as a competitive inhibitor of lipase with an IC50 value of 49 µM. In the present study, an attempt was made to identify stronger inhibitors from the ChEMBL database of bioactive compounds, as compared to the reference compound Bromhexine. Following docking and MD simulations, four hit compounds (N1-N4) were selected that showed promising binding modes and low RMSD values indicative of stable protein-ligand complexes. From subsequent binding pose metadynamics (BPMD) simulations, two of these (N2 and N4) stood out as more potent than Bromhexine, displaying stable interactions with residues in the catalytic site of the enzyme. Biological investigations were performed for all four compounds. Among them, the same two hit compounds were found to be the most effective binders with IC50 values of 22.1 and 27.5 µM, respectively; i.e. roughly twice as efficient as the reference Bromhexine. Taken together, our results show that these hits can be promising new candidates to use as leads for the development of drugs targeting the P. aeruginosa lipase enzyme.Communicated by Ramaswamy H. Sarma.

Development and evaluation of a colorimetric LAMP-based biosensor for rapid detection of a nosocomial infection agent, Citrobacter freundii.

Simple and fast diagnosis of Citrobacter freundii which is an important cause of nosocomial infection in human is crucial to achieve early treatment. We have developed and evaluated an optical LAMP-based biosensor for the visual detection of C. freundii for the first time. The efficiency of the assay was investigated and compared to PCR method. The selectivity and specificity of the biosensor were analyzed using Morganella morganii, Enterobacter aerogenes, Pseudomonas aeruginosa, Yersinia enterocolitica, Shigella sonnei, Serratia marcescens, Burkholderia cepacia and Klebsiella pneumoniae and a mixed-culture medium. Endpoint analysis using hydroxy naphthol blue was applied, and the color change to sky blue and no color change from violet indicated positive and negative results, respectively. The absorption at 650 nm was measured 0.39 for the positive sample, while the mean absorption of the test samples, including water, was 0.23. The specificity of the method was equal to that of PCR. However, the sensitivity was determined as 12.24 fg/µL of the genomic content of C. freundii, higher than PCR assay. The developed LAMP-based method provided a rapid and accurate technique for molecular diagnostics of C. freundii, making it a suitable technique for point-of-care diagnostics in cases of urgent situations.

Structural Insights into Pseudomonas aeruginosa Exotoxin A-Elongation Factor 2 Interactions: A Molecular Dynamics Study.

Exotoxin A (ETA) is an extracellular secreted toxin and a single-chain polypeptide with A and B fragments that is produced by Pseudomonas aeruginosa. It catalyzes the ADP-ribosylation of a post-translationally modified histidine (diphthamide) on eukaryotic elongation factor 2 (eEF2), which results in the inactivation of the latter and the inhibition of protein biosynthesis. Studies show that the imidazole ring of diphthamide plays an important role in the ADP-ribosylation catalyzed by the toxin. In this work, we employ different in silico molecular dynamics (MD) simulation approaches to understand the role of diphthamide versus unmodified histidine in eEF2 on the interaction with ETA. Crystal structures of the eEF2-ETA complexes with three different ligands NAD+, ADP-ribose, and ßTAD were selected and compared in the diphthamide and histidine containing systems. The study shows that NAD+ bound to ETA remains very stable in comparison with other ligands, enabling the transfer of ADP-ribose to the N3 atom of the diphthamide imidazole ring in eEF2 during ribosylation. We also show that unmodified histidine in eEF2 has a negative impact on ETA binding and is not a suitable target for the attachment of ADP-ribose. Analyzing of radius of gyration and COM distances for NAD+, ßTAD, and ADP-ribose complexes revealed that unmodified His affects the structure and destabilizes the complex with all different ligands throughout the MD simulations.

In silico and in vitro studies confirm Ondansetron as a novel acetylcholinesterase and butyrylcholinesterase inhibitor.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is growing rapidly among the elderly population around the world. Studies show that a lack of acetylcholine and butyrylcholine due to the overexpression of enzymes Acetylcholinesterase (AChE) and Butyrylcholinesterase (BChE) may lead to reduced communication between neuron cells. As a result, seeking novel inhibitors targeting these enzymes might be vital for the future treatment of AD. Ondansetron is used to prevent nausea and vomiting caused by chemotherapy or radiation treatments and is herein shown to be a potent inhibitor of cholinesterase. Comparison is made between Ondansetron and FDA-approved cholinesterase inhibitors Rivastigmine and Tacrine. Molecular docking demonstrates that interactions between the studied ligand and aromatic residues in the peripheral region of the active site are important in binding. Molecular dynamics simulations and binding pose metadynamics show that Ondansetron is highly potent against both enzymes and far better than Rivastigmine. Inhibitor activities evaluated by in vitro studies confirm that the drug inhibits AChE and BChE by non-competitive and mixed inhibition, respectively, with IC50 values 33 µM (AChE) and 2.5 µM (BChE). Based on the findings, we propose that Ondansetron may have therapeutic applications in inhibiting cholinesterase, especially for BChE.

Does dexamethasone inhibit glucose oxidase: an analysis in kinetics and molecular study.

OBJECTIVES: Glucose oxidase is an enzyme that is widely used in biosensors, especially kits for measuring blood sugar. Many diabetics use this type of kit to determine their blood sugar level. Aspergillus niger is the most important source of glucose oxidase for use in biosensors. Diabetes causes secondary diseases in patients for which medications are prescribed to improve them. Dexamethasone, a corticosteroid, is one of the drugs prescribed to diabetics to cure some secondary diseases. In this study, the effect of this drug on glucose oxidase was investigated from a kinetic and molecular point of view. METHODS: In this study, the kinetics of drug binding to the enzyme was measured and the type of inhibition was determined by Lineweaver-Burk plot. The Ki value of the drug was determined by drawing the secondary curve. Using fluorescence spectrophotometry and molecular docking, the binding of the drug to the enzyme was confirmed. RESULTS: The results showed that the drug inhibits the enzyme non-competitively. Determining the kinetics parameters of the drug-enzyme interaction showed that the drug acts as a potent inhibitor. Study at the molecular level by fluorescence spectrophotometer showed that the drug attachment alters the enzyme conformation to more compaction. In silico results showed that the drug is placed between two helices that are outside the active site and binds to the enzyme by three hydrogen bonds. CONCLUSIONS: The result of this study is useful because it suggests that in diabetic patients taking dexamethasone, the amount of glucose declared by the kit may not be real due to the inhibition of glucose oxidase.

Neuroprotective Effect of Root Extracts of Berberis Vulgaris (Barberry) on Oxidative Stress on SH-SY5Y Cells.

Objectives: Oxidative stress plays a key role in chronic and acute brain disorders and neuronal damage associated with Alzheimer disease (AD) and other neurodegeneration symptoms. The neuroprotective effects of berberine and Berberis vulgaris (barberry) root extract against apoptosis induced by hydrogen peroxide (H2O2) in the human SH-SY5Y cell line were studied. Methods: The methanolic extraction of barberry root was performed using a maceration procedure. Oxidative stress was induced in SH-SY5Y cells by H2O2, and an MTT assay was applied to evaluate the neuroprotective effects of berberine and barberry root extract. The cells were pretreated with the half maximal inhibitory concentration (IC50) of each compound (including berberine, barberry root extract, and H2O2), and the anti-apoptotic effects of all components were investigated using RT-PCR. Results: The SH-SY5Y cell viability increased in both groups exposed to 75 and 150 ppm barberry extract compared with that in the H2O2-treated group. The data showed that exposing SH-SY5Y cells to 30 ppm berberine significantly increased the cell viability compared with the H2O2-treated group; treatment with 150 and 300 ppm berberine and H2O2 significantly decreased the SH-SY5Y cell viability and was associated with berberine cytotoxicity. The mRNA levels of Bax decreased significantly under treatment with berberine at 30 ppm compared with the control group. A significant increase in Bcl-2 expression was observed only after treatment with the IC50 of berberine. The expression level of Bcl-2 in cells exposed to both berberine and barberry extracts was also significantly higher than that in cells exposed to H2O2. Conclusion: The outcomes of this study suggest that treatment of SH-SY5Y cells with barberry extract and berberine could suppress apoptosis by regulating the actions of Bcl-2 family members.

Bromhexine and its inhibitory effect on lipase - kinetics and structural study.

Lipase hydrolyses the ester bonds in triglyceride. It is an important enzyme in medicine and industry. Some pathogen bacteria use this exoenzyme to disrupt the extracellular matrix of host organisms. Pseudomonas uses various extracellular enzymes such as lipase to invade its host. In this report, for the first time, bromhexine was introduced as an inhibitor of lipase. Bromhexine is a mucolytic drug which is used in the treatment of respiratory tract disorders. The results showed that bromhexine inhibited the enzyme by competitive inhibition. IC50 and Ki values of the drug were 0.049 mM and 0.02 mM, respectively. Arrhenius plot showed that the drug reduced the activation energy. The enzyme was purified and SDS-PAGE showed that its molecular weight is 13 kDa. Fluorescence measurement revealed that binding of the drug to lipase could make structural changes in the enzyme. Inhibition of lipase by bromhexine could be applicable in medicine.

Development of one-pot single specific primer-LAMP (SSP-LAMP) for identification of Shigella genus using 16S rDNA.

Ribosomal RNA gene as a high-copy number nucleo-biomarker is extremely conserved among bacteria which limits its application to the discriminative detection approaches. We have developed a colorimetric isothermal amplification method called "single specific primer-LAMP (SSP-LAMP)" requiring only one specific primer for the amplification of the target and applied to the identification of the 16S rRNA gene in the Shigella genus. A region with high sequence homology in the genus and low homology with other bacteria was considered as the most appropriate. In that regard, a 23 bp sequence in the 16S rRNA gene of the genus was targeted based on the alignment of the gene with fifty-three closely related bacterial species, and a single specific primer along with five degenerate primers were designed. Using hydroxy-naphthol blue (HNB) as an indicator and gel electrophoresis, the proposed approach of SSP-LAMP was able to detect S. boydii, S. sonnei, S. flexneri and S. dysenteriae specifically while other species remained unidentified. The SSP-LAMP method could provide a rapid one-pot point-of-care method for molecular diagnostics of pathogens in many circumstances mainly samples with high genetic homogeneity.

Corrigendum: Inhibitory Effect of Codeine on Sucrase Activity.

A typographical error appeared in the author's name of the article entitled "Inhibitory Effect of Codeine on Sucrase Activity" by Dariush Minai-Tehrani, Saeed Minoui, Marzie Sepehre, Zohre Sharif-Khodai, Tooka Aavani, Drug Metabolism Letters, 2009; 3(1): 58-60. [1]. Details of the error and a correction are provided here. The fourth author's name in this article was misspelled. Hence it should be read as "Zohreh Sharifkhodaei" as per the request of the author. We regret the error and apologize to readers. The original article can be found online at: https://www.eurekaselect.com/93132/article Original: Zohre Sharif-Khodai Corrected: Zohreh Sharifkhodaei.

Effect of Tween Type Non-Ionic Detergent on the Activity of Lipase of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a Gram-negative and rod-shaped bacterium. It can use a variety of carbon sources and grow in different culture media. Its versatile extracellular enzymes give it the ability to grow on complex carbon sources. One of the most important enzymes of this bacterium is lipase, which is an extracellular enzyme. Lipases are one of the most useful enzymes in medicine and industry, especially in the detergent industry. In recent years, lipases have become an important component of detergent powders, so it is important to evaluate the performance of lipases in the presence of detergents. The aim of this study was to investigate the effect of non-ionic detergents Tween 20 and 80 on the activity of the Pseudomonas lipase. These detergents reduced Km and increased Vmax of the enzyme. The enzyme activity increased in the presence of these detergents at optimal pH and temperature. Conformational studies with the purified enzyme by fluorescence spectrophotometry showed that in the presence of Tween 20 and 80, there was a hypochromicity in emission peak of the enzyme, which indicated that the enzyme became less compact in vicinity of these detergents.

Development and evaluation of an improved quantitative loop-mediated isothermal amplification method for rapid detection of Morganella morganii.

A point-of-care diagnostic kit was developed for detection of Morganella morganii using optimized loop-mediated isothermal amplification (LAMP) technique within less than an hour. In that regard, dimethyl sulfoxide (DMSO) was utilized together with betaine and all variables were optimized to improve the efficiency of the method. Moreover, surface presentation of antigens protein was targeted and six unique primers were designed. Endpoint turbidity analysis was performed at 550 nm to measure the tetravalent anion (pyrophosphate) released during the reaction. The specificity of the method was evaluated using nine closely related bacterial species as well as its sensitivity. It was shown that the improved LAMP assay could significantly distinguish M. morganii from other bacteria while the sensitivity was determined to be 0.2 CFU mL-1.

An improvement in productive and reproductive performance of aged broiler breeder hens by dietary supplementation of organic selenium.

This study was conducted to determine the optimum level of home-made selenium-enriched yeast (SeY) in the diet of broiler breeder hens and to compare the effects of this product with sodium selenite (SS) or Selemax (SM) on their productive and reproductive performance. A total of 150 broiler breeder hens were divided to six groups and hens in each group were received a basal diet containing no selenium (CG), 0.15, 0.30, 0.45 mg SeY/kg diet (SeY-0.15, SeY-0.30 and SeY-0.45, respectively), 0.30 mg SM/kg diet or 0.30 mg SS/kg diet for 15 successive weeks. The results showed that egg weight and production and hatchability rate were higher in SeY-0.45 compared to other groups (P < 0.05). Also, SeY-0.45 group led to lower embryonic mortality rate compared to CG and SS groups. Fertility rate and chick quality parameters were not affected by selenium supplementation during this period (P > 0.05). In conclusion, the dietary supplementation of home-made selenium, as an organic selenium source, can be used to improve the productive and reproductive performance in aged broiler breeder hens at 0.45 mg/kg feed.

Effect of sinapic acid on memory deficits and neuronal degeneration induced by intracerebroventricular administration of streptozotocin in rats.

The present study aimed to elucidate the neuroprotective effect of sinapic acid on intracerebroventricular streptozotocin (ICV-STZ) induced neuronal loss and memory impairment. To test this hypothesis, male Wistar rats were randomly divided into 11 groups: normal control, sham-operated control, sinapic acid (2.5, 5, 10, and 20 mg/kg bw intragastrically, daily) alone, Alzheimer control rats (ICV-STZ, 3 mg/kg bw), sinapic acid (2.5, 5, 10, and 20 mg/kg bw intragastrically, daily) together with STZ, and the treatment was performed accordingly. After 28 days of ICV-STZ administration, the animals were assessed for cognitive performance using passive avoidance test and then sacrificed for biochemical and histopathological examinations. Sinapic acid was found to be effective in improving antioxidant status and preventing memory loss in Alzheimer rats. Moreover, TNF-α level in the hippocampus was significantly decreased by sinapic acid. Also, administration of sinapic acid significantly increased the levels of antioxidant enzymes and decreased malondialdehyde level in the hippocampus. Histopathological examination showed that sinapic acid reduced cell loss in the cerebral cortex and hippocampus in Alzheimer's rats. The present study suggests that sinapic acid is effective in the prevention of memory loss and improvement of oxidative stress and might be beneficial in the treatment of Alzheimer's disease.

Temporal Pattern and Crosstalk of Necroptosis Markers with Autophagy and Apoptosis Associated Proteins in Ischemic Hippocampus.

Necroptosis, a novel type of programmed cell death, has been recently implicated as a possible mechanism for cerebral ischemia-reperfusion (I/R) injury. We herein studied time-dependent changes of necroptosis markers along with apoptosis- and autophagy-associated proteins in rat hippocampus at 1, 3, 6, 12, 24, and 48 h after global cerebral I/R injury. Furthermore, to determine the cross talk between autophagy and necroptosis, we examined the effects of pretreatment with bafilomycin-A1 (Baf-A1), as a late-stage autophagy inhibitor, on necroptosis. Highest levels of receptor-interacting protein 1 and 3 (RIP1 and RIP3), as key mediators of necroptosis, were observed at 24 h after reperfusion. Alongside, activity of glutamate dehydrogenase (GLUD1), downstream enzyme of RIP3, was increased. Peak time of necroptosis was subsequent to caspase-3-dependent cell death that peaked at 12 h of reperfusion but concurrent with autophagy. Administration of Baf-A1 could attenuate necroptosis, verified by decrease in RIP1 and RIP3 protein levels, as well as GLUD1 activity. However, there was no significant change in caspase-3-dependent cell death. Taken together, our results highlight that global cerebral I/R activates necroptosis that could be triggered by autophagy and interacts reversely with caspase-3-dependent apoptosis.

Inhibitory action of dicyclomine on lipase activity, kinetics and molecular study.

Lipase is one of the most important groups of enzymes for industry and medicine. It breaks down triacylglycerol to glycerol and fatty acids. Some bacteria use lipase to degrade the extracellular matrix of the host cells to penetrate into the tissues. Dicyclomine is a muscarinic antagonist receptor that relieves the smooth muscle spasm of the gastrointestinal tract and affects the cardiovascular system. In this research, the effect of a dicyclomine on the lipase activity of Pseudomonas aeruginosa was studied. Hanes-Woolf plot showed that the drug inhibited the enzyme by competitive inhibition. The IC50 value (60uM) and Ki (30uM) of the drug revealed that the drug bound to enzyme with high affinity. Determination of enzyme activity in various temperature showed that the maximum activity of lipase was at 60°C both in the presence and absence of the drug. Arrhenius plot determined that the activation energy of the enzyme reaction was increased in the presence of the drug. The model of binding demonstrated that the drug entered a pocket containing 10 amino acids and interacted by hydrogen bond and hydrophobic interaction and the conformational change of the enzyme after binding of the drug was confirmed by fluorescence measurement.

Interaction of Antipsychotic Drugs with Sucrase, Kinetics and Structural Study.

BACKGROUND: In patients with the Congenital Sucrase-Isomaltase Deficiency (CSID), who lack intestinal sucrase-isomaltase enzyme, a suspension of yeast sucrase is applied as a drug to compensate the enzyme deficiency. While antipsychotic drugs are used for the treatment of schizophrenia, administering multiple drugs at the same time may counteract each other. METHODS: In this study, the interaction between trifluoperazine and haloperidol as antipsychotic drugs on oral drug yeast sucrase was investigated. In this regard, the kinetic parameters of enzyme were determined in the presence or absence of the drugs. The kinetic parameters of the drugs such as Ki and IC50 were also calculated. Lineweaver - Burk plot was used to reveal the type of inhibition. RESULTS: The results showed that both drugs could reduce sucrase activity and decrease the Vmax of the enzyme by non-competitive inhibition. The IC50 and Ki values of the drugs were determined to be 0.7 and 0.068 mM and 0.45 and 0.063 mM for haloperidol and trifluoperazine, respectively. The results suggested that trifluoperazine binds to the enzyme with higher affinity than haloperidol. Fluorescence measurement was used for conformational investigations of the drugs and sucrase interaction. It was shown that the drugs bind to free enzyme and enzyme-substrate complex which are accompanied with hyperchromicity. This suggests that tryptophan residues of the enzyme transferred to hydrophobic medium after binding of the drugs to the enzyme. CONCLUSION: The finding of this research revealed that both trifluoperazine and haloperidol could inhibit sucrase in non-competitive manner. The kinetic parameters and conformational changes due to binding of trifluoperazine to the enzyme were different from that of haloperidol.

Inhibition of pseudoperoxiadse activity of human red blood cell hemoglobin by methocarbamol.

After red blood cells lysis, hemoglobin is released to blood circulation. Hemoglobin is carried in blood by binding to haptoglobin. In normal individuals, no free hemoglobin is observed in the blood, because most of the hemoglobin is in the form of haptoglobin complex. In some diseases that are accompanied by hemolysis, the amount of released hemoglobin is higher than its complementary haptoglobin. As a result, free hemoglobin appears in the blood, which is a toxic compound for these patients and may cause renal failure, hypertensive response and risk of atherogenesis. Free hemoglobin has been determined to have peroxidase activity and considered a pseudoenzyme. In this study, the effect of methocarbamol on the peroxidase activity of human hemoglobin was investigated. Our results showed that the drug inhibited the pseudoenzyme by un-competitive inhibition. Both Km and Vmax decreased by increasing the drug concentration. Ki and IC50 values were determined as 6 and 10mM, respectively. Docking results demonstrated that methocarbamol did not attach to heme group directly. A hydrogen bond linked NH2 of carbamate group of methocarbamol to the carboxyl group of Asp126 side chain. Two other hydrogen bonds could be also observed between hydroxyl group of the drug and Ser102 and Ser133 residues of the pseudoenzyme.

Binding of Cimetidine to Balb/C Mouse Liver Catalase; Kinetics and Conformational Studies.

Catalase is responsible for converting hydrogen peroxide (H2O2) into water and oxygen in cells. This enzyme has high affinity for hydrogen peroxide and can protect the cells from oxidative stress damage. Catalase is a tetramer protein and each monomer contains a heme group. Cimetidine is a histamine H2 receptor blocker which inhibits acid release from stomach and is used for gasterointestinal diseases. In this research, effect of cimetidine on the activity of liver catalase was studied and the kinetic parameters of this enzyme and its conformational changes were investigated. Cell free extract of mouse liver was used for the catalase assay. The activity of the catalase was detected in the absence and presence of cimetidine by monitoring hydrogen peroxide reduction absorbance at 240 nm. The purified enzyme was used for conformational studies by Fluorescence spectrophotometry. The data showed that cimetidine could inhibit the enzyme in a non-competitive manner. Ki and IC50 values of the drug were determined to be about 0.75 and 0.85 uM, respectively. The Arrhenius plot showed that activation energy was 6.68 and 4.77 kJ/mol in the presence and absence of the drug, respectively. Fluorescence spectrophotometry revealed that the binding of cimetidine to the purified enzyme induced hyperchromicity and red shift which determined the conformational change on the enzyme. Cimetidine could non-competitively inhibit the liver catalase with high affinity. Binding of cimetidine to the enzyme induced conformational alteration in the enzyme.

Enhancing effect of cimetidine on peroxidase activity of human erythrocyte hemoglobin.

BACKGROUND: Hemoglobin is released to the serum after erythrocyte lyses. Haptoglobin is responsible for carrying hemoglobin into the serum. In hemolytic disease, the amount of hemoglobin which is released to the serum is high; however, the amount of haptoglobin is not enough for binding all the released hemoglobins. Free hemoglobin has peroxidase activity (a pseudoenzyme) and has been indicated to be harmful for patients. This study is focused on the effect of cimetidine on peroxidase activity of hemoglobin. METHODS: Erythrocytes were lysed to obtain hemoglobin. Peroxidase activity of hemoglobin was detected using o-dianisidine and H(2)O(2) as substrates. RESULTS: Our results showed that the drug operated as an activator for the pseudoenzyme. Cimetidine bound to the pseudoperoxidase in an un-competitive manner and decreased the Km. Half maximal effective concentration (EC(50)) of cimetidine was determined to be about 12.5 mM. Alkaline pH increased the rate of reaction. Arrhenius plot showed that the activation energies of reactions in the absence and presence of drug were about 10.5 kJ/mol and 7.65 kJ/mol, respectively. CONCLUSIONS: The results demonstrated that cimetidine activates the peroxidase activity of free hemoglobin. Hence, it is suggested that the prescription of cimetidine for the patients with hemolyses diseases may enhance the harmful effects of free hemoglobin in these patients.