[Research progress on Mycobacterium tuberculosis acetyltransferase]

The protein acetylation of Mycobacterium tuberculosis(MTB) plays an important role in virulence, drug resistance, regulation of metabolism and host anti-tuberculosis immune response. The proteins acetylation of MTB and host protein could be induced by the MTB acetyltransferase, which is related to the occurrence, development and prognosis of tuberculosis (TB). A clear understanding of the function of MTB acetyltransferase and identification of its targeted regulatory protein acetylation modification is critical to elucidate the pathogenic mechanism and drug resistance mechanism of TB, and then this could then provide new targets for the development of anti-tuberculosis drugs. This article systematically reviewed the research progress on MTB acetyltransferase related functions, which will provide a theoretical basis for further research on its mediated protein acetylation modification, further development of new anti-tuberculosis drugs and elucidation of drug resistance mechanism.

[Periprosthetic gout flare after total knee arthroplasty: A misdiagnostic case report]

Periprosthetic gout flare is a rare arthritic condition after total knee arthroplasty, but the symptoms of gout may have often been mistaken as acute periprosthetic infection given their similarity. Misdiagnosis as periprosthetic infection can lead to unnecessary surgery, long-term dependence on anti-biotics, and even malfunction of the involved knee joint. Here, we report a case study of a patient with immunodeficiency condition of long-term oral glucocorticoid and diabetes mellitus, who had undergone a knee replacement 8 weeks before. The initial symptoms of fever and joint pain together with the dysfunction of her right knee with elevated inflammatory markers, such as increased serum leukocytes, erythrocyte sedimentation rate, C-reactive protein, and synovial cell counts led to a diagnosis of acute periprosthetic infection. Arthrocentesis and bacterial culture were performed preoperatively. According to the current Musculoskeletal Infection Society (MSIS) criteria for diagnosis of periprosthetic infection, the case was classified as periprosthetic infection and a prosthesis retained debridement surgery was performed. However we got negative culture results in all the pre-operative and intro-operative samples. The symptoms as well as the laboratory inflammatory markers improved shortly after the debridement surgery until the 11th day when all the similar systemic and local symptoms recurred. With a remedial crystal analysis of synovial fluid from the patient, gouty flare was found to be the cause of acute arthritis finally. Accor-dingly, after anti-gout medications were administrated, the symptoms associated with acute arthritis gra- dually subsided, and there was no recurrence during a 24-month follow-up. This article described the cli-nical manifestation, diagnosis and differential diagnosis, treatment of a case of periprosthetic gout. Although relatively rare, gout should be considered as a differential diagnosis in suspected periprosthetic infection. Current criteria for periprosthetic infection can not exclude the diagnosis of periprosthetic gout flare, it is therefore imperative that the analysis of joint aspirate for crystals be conducted to determine the correct course of treatment, or unnecessary surgical procedure may be performed in periprosthetic gout case.

[Research progress in non-coding RNAs in mediating immune responses of macrophages to Mycobacterium tuberculosis infection]

Tuberculosis (TB) is a chronic infectious disease caused by mycobacterium tuberculosis (MTB) infection. Macrophages are the first line in defensing MTB infection and the main host cells for the growth and persistence of MTB. Changes in macrophage function are critical for the host response to tuberculosis. Non-coding RNAs are involved in the pathophysiological process of many diseases, including TB, and play a very important regulatory role in the macrophage mediated immune response process. Therefore, we reviewed the mechanisms of the non-coding RNAs mediated function alteration of macrophages, in order to facilitate identification of potential therapeutic targets for host-directed anti-TB treatment.

[Diagnostic performance of a novel Mycobacterium Tuberculosis specific T-Cell based assay for tuberculosis]

Objective: To evaluate the diagnosic performance of a novel Mycobacterium tuberculosis (MTB) specific T-cell based assay for tuberculosis, which targets the mRNA detection of interferon gamma-induced protein 10 (IP-10). Methods: Suspected tuberculosis patients were prospectively and consecutively recruited in Beijing Chest Hospital between March 2018 and November 2019, and individuals with lower risk of MTB infection were also recruited. IP-10.TB and T-SPOT.TB assays were simulataneously performed on peripheral blood samples. The diagnostic performance of IP-10.TB and T-SPOT.TB were analyzed using the receiver operating characteristic curve. Accordance of IP-10.TB and T-SPOT.TB was analyzed by Cohen's kappa test, while the correlation between the expression level of IP-10 mRNA in IP-10.TB test and the number of SFCs in T-SPOT.TB test were analyzed by Pearson correlation test. Results: A total of 235 patients with tuberculosis, 110 patients with other diseases and 153 individuals with lower risk of MTB infection were included in the final analysis. No significant difference was detected in the rate of indeterminate results between IP-10.TB assay (3/498, 0.60%) and T-SPOT.TB assay (6/498, 1.21%). The total sensitivity and specificity of IP-10.TB assay were 91.3% (95%CI 86.8%-94.6%) and 81.1% (95%CI 75.8%-85.7%). The specificity of IP-10.TB in individuals with lower risk of MTB infection was 98.0% (95%CI 94.4%-99.6%). The total sensitivity and specificity of T-SPOT.TB assay were 93.0% (95%CI 88.9%-96.0%) and 83.8% (95%CI 78.7%-88.1%). The specificity of T-SPOT.TB in individuals with lower risk of MTB infection was 100% (95%CI 97.6%-100.0%). No significant differences were detected in sensitivity and specificity between IP-10.TB and T-SPOT.TB assays (P>0.05). The positive coincidence rate of these 2 methods was 91.0% (95%CI 87.5%-94.5%), and the negative coincidence rate was 88.9% (95%CI 84.9%-92.9%) and the total coincidence rate was 90.0% (95%CI 87.3%-92.6%). The Cohen's kappa value was 0.80 (95%CI 0.75-0.85, P<0.001) between IP-10.TB and T-SPOT.TB assays. Conclusion: These results showed that the diagnostic performance of IP-10.TB was consistent with that in T-SPOT.TB, and this test could be a novel adjunctive tool for the diagnosis of tuberculosis.

[The effects of long-term exposure to silica dust on serum CC16 and KL-6 levels]

Objective: To investigate the effects of long-term exposure to silica dust on serum CC16 and KL-6 levels. Methods: The patients with stage I silicosis who were hospitalized in our hospital from April 2016 to April 2017 were treated as silicosis group. The silica dust exposed workers without silicosis who were taken the physical examination in our hospital were taken as a dust-exposed group. The healthy control group comes from in the same period of community physical examination did not touch the dust. The levels of CC16 and KL-6 in serum of all subjects were determined by enzyme-linked immunosorbent assay (ELISA) , and the levels of CC16 and KL-6 in serum were compared in three groups. Results: Compared with the control group, the serum levels of CC16 in the silicosis group (P<0.01) and the dust-exposed group (P<0.01) were significantly lower. Compared with the control group, the level of serum KL-6 in the silicosis group was significantly decreased (P<0.01) compared with the control group, while the level of KL-6 in the serum of the dust-exposed group was significantly increased (P<0.01) . The ROC area of CC16 for diagnosis of silicosis was 0.92 (P<0.01) , with a sensitivity of 81.37%, specificity of 92.63% and Kappa value of 0.74. Conclusion: Long-term exposure to silica dust may lead to a decrease in serum CC16 levels. Reduced serum CC16 levels may be useful in identifying the diagnosis of silicosis.

[Epidemiological characteristics of pesticide poisoning in Xuzhou city from 2005 to 2017]

Objective: To understand the characteristics and causes of pesticide poisoning in Xuzhou city, and provide basis for formulating prevention and control measures. Methods: The cases of pesticide poisoning in Xuzhou City from 2005 to 2017 were collected from "Pesticide Poisoning Report Card" . The data were analyzed and assessed by EpiData. The SPSS 22.0 software was used for statistical analysis. Results: During the thirteen years, there were a total of 8092 cases of pesticide poisoning, among which, the number of occupational pesticide poisoning was 1 408, accounting for 17.4% of the total number of cases, 14 patients died, the case fatality rate was 0.1%. There were 2, 992 cases of male poisoning, accounting for 36.97% of the total number of cases, and 5, 100 cases of female poisoning, accounting for 63.03%. There were 6684 non-productive pesticide poisonings, accounting for 82.6% of the total number of cases; 387 deaths occurred, and the mortality rate was 5.8%. Among non-productive poisonings, the incidence of oral pesticide poisoning was 84.3%, and the incidence of accidental poisoning by pesticides was 15.7%. Organophosphorus pesticides poisoning cases accounted for the majority of oral pesticide poisoning cases. The overall incidence of pesticide poisoning showed a downward trend. The age of non-productive pesticide poisoning cases was mainly 15-44 years old, and the number of cases of poisoning were 4 029 cases (60.28%) . With the increase of age, the mortality rate of poisoning cases was higher, especially for those over 60 years old who died of oral pesticide poisoning (40.1%) . The peak of pesticide poisoning began to increase in the second quarter and reached its peak in the third quarter. Conclusion: Although the cases of pesticide poisoning reported in Xuzhou City have been declining in recent years, the situation is still severe. The proportion of oral pesticide suicide accounts for a large proportion, and the mortality rate of elderly and female is relatively high, and the government should pay more attention. Workers should conduct safety education and psychological counseling to improve the knowledge and consciousness of safe use of pesticides.

[Study on the effect of occupational exposure to glyphosate on blood routine]

Objective: To investigate the effect of glyphosate on blood routine of occupational exposure population. Methods: The workers who were occupationally exposed to glyphosate were selected as exposure group, and administrative staffs who were not exposed to glyphosate were selected as control group. Occupational health examination was conducted on all the subjects, and personal monitoring was applied to detect the concentration of glyphosate in the air of workplace. Time weighted average (TWA) concentration was calculated by the result of determination. Statistical methods were employed to compare the difference of blood routine results between the contact group and the control group, as well as between different posts. Results: 178 glyphosate workers were included in the contact group, and 203 non-contact persons were included in the control group. There was no statistically significant difference in the equilibrium test between the two groups(P>0.05). The abnormal rate of blood routine in the exposure group and the control group were 70.8% and 69.0%, respectively, but the difference was not statistically significant (P>0.05). Compared with the control group, the red blood cell count and platelet distribution width difference (P<0.05) were significant difference. There was no significant difference between different positions (P>0.05). Conclusion: When TWA value is below 9.40 mg/m(3), glyphosate has effect on the results of platelet distribution width and red blood cell count, but has no effect on the abnormal rate of blood routine.

[Study of the effect of occupational exposure to glyphosate on hepatorenal function]

Objective: To explore the effect of occupational exposure to glyphosate on hepatorenal function. Methods: 526 workers who were occupationally exposed to glyphosate from 5 glyphosate-producing factories were selected as cases; and another 442 administrative staffs who were not exposed to glyphosate were selected as controls from April to November, 2014. All the subjects accepted occupational health examination. The concentration level of glyphosate in the air of workshop was detected and the time weighted average concentration (TWA) was calculated. And analyze the difference of hepatorenal fuction between case group and control group. Result: The age of the subjects in the case and control groups were separately (35.6±10.3), (34.3±9.7) years old, with the length of working for (6.5±5.7), (7.7±6.8) years. The TWA of glyphosate in the case group was between <0.03-48.91 mg/m(3), with the geometric mean at 3.78 mg/m(3). The overall rates of abnormal hepatic and renal function in the case group were 14.4% (76 cases) and 16.2% (85 cases), respectively; while those were 5.0% (22 cases) and 4.8% (21 cases), respectively in control group, and the difference showed statistical significance (P<0.05). When TWA reached <0.03-6.00 mg/m(3), the difference of hepatorenal fuction between case group and control group showed statistical significance, and the rates of abnormal hepatic and renal function was 8.0% (36/447) and 9.8% (44/447) respectively in case group. When cumulative exposure level reached <1.56-68.64 g, the difference of hepatorenal fuction between case group and control group showed statistical significance, and the rates increased to 9.2% (37/404) and 10.4% (42/404) respectively in group of cases. Conclusion: Glyphosate can affect the hepatic and renal function among occupational exposure population, and there was an association between the effect and the exposure dose.

[Novel biomarkers for latent tuberculosis infection by plasma proteomic profiling]

OBJECTIVE

To screen specific biomarkers for latent tuberculosis infection by comparing the plasma proteomic profiling between latent tuberculosis infection and healthy controls.

METHODS

The plasma proteins from 15 cases with latent tuberculosis infection and 15 healthy controls were detected by the label-free quantitative proteomic technology. Differential expressed proteins were analyzed by GO, KEGG, and BiNGO analysis. Student's t test was used to analyze the differential expression between 2 groups.

RESULTS

Twenty-three candidate proteins were identified, among which 15 proteins were downregulated (<0.5-fold at P<0.05) and 8 proteins were upregulated (>2.0-fold at P<0.05) in the latent tuberculosis infection group. Bioinformatic analysis revealed 3 proteins AAT, C3 and C4A to be the most significant.

CONCLUSION

There were differential plasma protein profiles between latent tuberculosis infection and healthy controls. Candidate proteins AAT, C3 and C4A were promising biomarkers for discriminating cases with latent tuberculosis infection from healthy persons.

[Hydrogen sulfide in cartilage and its inhibitory effect on matrix metalloproteinase 13 expression in chondrocytes induced by interlukin-1β]

OBJECTIVE

To investigate whether endogenous hydrogen sulfide (H2S) was involved in the pathogenesis of osteoarthritis (OA) and its underlying mechanism, to detect H2S and its synthases expression in knee cartilage in patients diagnosed with different severity of OA, and to explore the transcription and expression of gene MMP-13 in chondrocytes treated with IL-1β or H2S.

METHODS

Synovial fluids of the in-patients with different severity of OA hospitalized in Peking University First Hospital were collected for measurement of H2S content using methylene blue assay. Articular cartilages of the patients who underwent knee arthroplasty were collected for the cell culture of relatively normal chondrocytes. The chondrocytes were cultured to the P3 generation and H2S molecular probes were used for detection of endogenous H2S generation in the chondrocytes. Immunocytochemistry was used to detect the localization of H2S synthases including cystathionine β-synthase (CBS), cystathionine-γ-lyase (CSE), and mercaptopyruvate sulfurtransferase (MPST) in OA chondrocytes. Western blot was used to quantify the protein expressions of CSE, MPST, and CBS in cartilage tissues of the patients who were diagnosed with OA and underwent knee arthroplasty. The relatively normal human chondrocytes were cultured to passage 3 and then divided into 4 groups for different treatments: (1)the normal control group, no reagent was added; (2)the IL-1β group, 5 μg/L of IL-1β was added; (3)the IL-1β+H2S group, 200 μmol/L of NaHS was added 30 min before adding 5 μg/L of IL-1β;(4)the H2S group, 200 μmol/L of NaHS was added. The transcription and expression of gene MMP-13 in chondrocytes of each group were determined with Real-time PCR and Western blot, respectively. And the total NF-κB p65 and phosphorylated NF-κB p65 in chondrocytes were detected with Western blot.

RESULTS

The content of H2S in the synovial fluid of degenerative knee was (14.3±3.3) μmol/L. Expressions of endogenous H2S and its synthases including CBS, CSE and MPST were present in the cytoplasm of chondrocytes.CSE protein expression in Grade 3 (defined by outerbridge grading) cartilage tissues was significantly increased as compared with that of Grade 1 cartilage tissues (1.67±0.09 vs. 1.26±0.11, P< 0.05). However, no significant difference of CBS or MPST expression among the different groups was observed. The expression of MMP-13 protein in the IL-1βgroup was significantly higher than that in the normal chondrocytes (1.87±0.67 vs. 0.22±0.10, P<0.05), and that in the IL-1β+H2S group was significantly decreased than that in the IL-1β group (0.55±0.11 vs. 1.87±0.67, P< 0.05), and that in the H2S group had no significant difference compared with that in the normal control group. The transcription of MMP-13 protein in the IL-1β group was significantly higher than that in the normal chondrocytes (31.40±0.31 vs. 1.00±0.00, P<0.05), and that in the IL-1β+H2S group was significantly decreased than that in the IL-1β group (24.41±1.28 vs. 31.40±0.31, P<0.05), and that in the H2S group had no significant difference compared with that in the normal control group. The total NF-κB p65 in the IL-1β group was significantly higher than that in the normal chondrocytes (2.13±0.08 vs. 0.73±0.08, P< 0.05), and that in the IL-1β+H2S group was significantly decreased than that in the IL-1β group (1.24±0.13 vs. 2.13±0.08, P<0.05), and that in the H2S group had no significant difference compared with that in the normal control group. The phosphorylated NF-κB p65 in IL-1β group was significantly higher than that in the normal chondrocytes (1.30±0.13 vs. 0.19±0.04, P<0.05), and that in IL-1β+H2S group was significantly decreased than that in the IL-1β group (0.92±0.26 vs. 1.30±0.13, P<0.05), and that in the H2S group had no significant difference compared with that in the normal control group.

CONCLUSION

H2S affected the cartilage degeneration by partly inhibiting the degradation of extracellular matrix.

Molecular characterization of HMW-GS 1Dx3(t) and 1Dx4(t) genes from Aegilops tauschii and their potential value for wheat quality improvement

Two x-type high molecular weight glutenin subunits (HMW-GS) in Aegilops tauschii, 1Dx3(t) and 1Dx4(t) were identified by SDS-PAGE and MALDI-TOF-MS. Their complete coding sequences were isolated by AS-PCR. 1Dx3(t) and 1Dx4(t) genes consist of 2535 bp and 2508 bp and encode 845 and 836 amino acid residues, respectively. The deduced molecular masses of 1Dx3(t) and 1Dx4(t) gene products are 87655.26 Da and 86664.24 Da, respectively, well corresponding to the molecular masses measured by MALDI-TOF-MS. A total of 18 SNPs were identified between 1Dx3(t) and 1Dx4(t). Comparing with 1Dx5 subunit, 1Dx3(t) had a six amino acid insertion at 146-151 while the 1Dx4(t) had a nine amino acid deletion when compared with 1Dx3(t) subunit. The authenticity of the cloned 1Dx3(t) and 1Dx4(t) genes were confirmed by successful expression of their ORFs in E. coli. Comparison and phylogenetic tree based on the amino acid and nucleotide sequences confirmed that 1Dx3(t) was most closely related to 1Dx5 subunit that is widely accepted as a superior subunit for bread-making property. The secondary structure prediction demonstrated that 1Dx3(t) subunit has significantly high α-helix and β-strand contents, suggesting it might have positive effects on dough quality.

In-vitro characterization of the cytochrome P450 isoenzymes involved in the back oxidation and N-dealkylation of reduced haloperidol

In-vitro studies were performed using human liver microsomes and c-DNA-expressed human P450 isoforms to identify the cytochrome P450 isoenzyme(s) involved in the back oxidation and N-dealkylation of reduced haloperidol. Back oxidation and N-dealkylation of reduced haloperidol were assessed by measuring the formation of haloperidol and 4-(4-chlorophenyl)-4-hydroxypiperidine (CPHP), respectively. The haloperidol and CPHP formation rates as a function of substrate concentration, measured in three livers, followed monophasic enzyme kinetics. For haloperidol formation Km values ranged from 51-59 microM, and Vmax values from 190-334 pmol mg(-1) min(-1); for CPHP formation Km values were 44-49 microM, and Vmax values 74-110 pmol mg(-1) min(-1). Haloperidol and CPHP formation rates in the nine liver preparations were significantly correlated with dextromethorphan N-demethylase activity (a marker of CYP3A4 activity), but not with the CYP2D6, CYP1A2 and CYP2C9 activity. Ketoconazole and troleandomycin, inhibitors of CYP3A4, inhibited competitively both haloperidol and CPHP formation, with a Ki value lower than 0.2 microM for ketoconazole and lower than 0.3 microM for troleandomycin. Sulphaphenazole (CYP2C9), furafylline (CYP1A2) and quinidine and paroxetine (CYP2D6) gave only little inhibition (IC50 > 60 microM). CPHP and haloperidol formation were, moreover, enhanced by alpha-naphthoflavone, an effect known for CYP3A4 mediated reactions. Anti-CYP3A4 antibodies strongly inhibited haloperidol and CPHP formation, whereas CYP2D6 antibodies did not. Among the recombinant human CYP isoforms tested, CYP3A4 exhibited the highest activity with respect to haloperidol and CPHP formation rates, with no detectable effect of CYP1A2, CYP2D6 and CYP2C9. These results strongly suggest that back oxidation and N-dealkylation of reduced haloperidol in human liver microsomal preparations are mediated by CYP3A4.

Characterization of the cytochrome P450 isoenzymes involved in the in vitro N-dealkylation of haloperidol

AIMS

The present study was carried out to identify the cytochrome P450 isoenzyme(s) involved in the N-dealkylation of haloperidol (HAL).

METHODS

In vitro studies were performed using human liver microsomes and c-DNA-expressed human P450 isoforms. N-dealkylation of HAL was assessed by measuring the formation of 4-(4-chlorophenyl)-4-hydroxypiperidine (CPHP).

RESULTS

There was a tenfold variation in the extent of CPHP formation amongst the nine human liver microsomal preparations. The CPHP formation rates as a function of substrate concentration, measured in three livers, followed monophasic enzyme kinetics. Km and Vmax values ranged respectively from 50 to 78 microM and from 180 to 412 pmol mg-1 min-1 CPHP formation rates in the nine liver preparations were significantly correlated with dextromethorphan N-demethylase activity (a marker of CYP3A4 activity), but not with the activity of dextromethorphan O-demethylase (CYP2D6), phenacetin O-deethylase (CYP1A2) or tolbutamide hydroxylase (CYP2C9). Ketoconazole, an inhibitor of CYP3A4, inhibited competitively CPHP formation (Ki=0.1 microM), whereas sulphaphenazole (CYP2C9), furafylline (CYP1A2) and quinidine (CYP2D6) gave only little inhibition (IC50 > 100 microM). CPHP formation was, moreover, enhanced by apha-naphtoflavone, an effect common to CYP3A4 mediated reactions. Anti-CYP3A4 antibodies strongly inhibited CPHP formation, whereas no inhibition was observed in the presence of CYP2D6 antibodies. Among the recombinant human CYP isoforms tested, CYP3A4 exhibited the highest activity with respect to CPHP formation rate, with no detectable effect of other CYP isoforms (CYP1A2, CYP2D6 and CYP2C9). HAL inhibited dextromethorphan O-demethylase (CYP2D6) with IC50 values between 2.7 and 8.5 microM, but not (IC50 > 100 microM) dextromethorphan N-demethylase (CYP3A4), phenacetin O-deethylase (CYP1A2) or tolbutamide hydroxylase (CYP2C9).

CONCLUSIONS

These results strongly suggest that the N-dealkylation of HAL in human liver microsomal preparations is mediated by CYP3A4.

Transient and time-resolved resonance Raman investigation of photoinitiated electron transfer in ruthenated cytochromes c

Ruthenation of exterior amino acid residues of heme proteins provides an effective means by which biological ET reactions can be studied within the context of highly complex protein environments. Resonance Raman spectroscopy can probe both ET kinetics and structural dynamics at the molecular level. Here we present the first comprehensive use of time-resolved and transient resonance Raman spectroscopies to examine photoinduced ET in cytochromes. Two ruthenated cytochromes c, Ru(lys72)-cyt.c and Ru(cyt102)cyt.c, were studied with TRRS using 10 ns laser pulses and with TRRRS on a 10 ns to 10 ms time scale. It was found that resonance Raman protocols can effectively trace ET kinetics and associated heme--protein structural dynamics. Care must be exercised, however, when drawing comparisons to measurements made by other methods (i.e., transient absorbance). The TRRS studies directly probe the heme and its local environment and reveal that the heme dynamics accompanying ET are very rapid relative to phenomenological ET kinetics. The heme and its local environment evolve to their equilibrium (ferrous) structure in less than 10 ns subsequent to ET, with no evidence for the existence of metastable heme pocket geometries analogous to those observed in the dynamic response of hemoglobins and oxidases. Finally, species-specific differences are observed in the photoinduced ET kinetics and heme structural dynamics. However, these differences are confined to nanosecond or faster time scales.

Photoperturbation of the heme a3-CuB binuclear center of cytochrome c oxidase CO complex observed by Fourier transform infrared spectroscopy

Purified cytochrome c oxidase CO complex from beef heart has been studied by Fourier transform infrared absorbance difference spectroscopy. Photolysis at 10-20 Kelvin results in dissociation of a3FeCO, formation of CuBCO, and perturbation of the a3-heme and CuB complex. The vibrational perturbation spectrum between 900 and 1700 cm-1 contains a wealth of information about the binuclear center. Appearance in infrared photoperturbation difference spectra of virtually all bands previously reported from resonance Raman spectra indicate the importance of polarization along the 4-vinyl:8-formyl axis, which results in the reduction of heme symmetry to C2v. Frequency-shifted bands due to the 8-formyl and 4-vinyl groups of the a3-heme have been identified and quantitated. The frequency shifts have been interpreted as being due to a change in porphyrin polarization with change in spin state of the iron by photodissociation of CO or perturbation of the CuB coordination complex.

The subunit location of magnesium in cytochrome c oxidase

The magnesium ion in bovine heart cytochrome c oxidase can be depleted up to 75% by heat treatment of the enzyme at 43 degrees C followed by dialysis against EDTA buffer solution. The magnesium-depleted enzyme so obtained retains 40% of the activity of the native enzyme. This is the first attempt to deplete magnesium ion from bovine heart cytochrome c oxidase without denaturation of the protein. Magnesium depletion exposes at least one carboxyl group on subunit IV for labeling by N-cyclohexyl-N'-(4-dimethylaminonaphthyl)carbodiimide (NCD-4). The NCD-4 labeling of subunit IV of the magnesium-depleted enzyme is significantly enhanced relative to what is observed for the native and heat-treated oxidase, suggesting that the magnesium ion is located in subunit IV with at least one carboxyl ligand. By comparing the activity of the magnesium-depleted enzyme with that of a control sample of heat-treated oxidase, the influence of divalent magnesium on the activity of the enzyme is assessed.

Intracomplex electron transfer between ruthenium-cytochrome c derivatives and cytochrome c oxidase

The reactions of bovine cytochrome c oxidase with horse cytochrome c derivatives labeled at specific lysine amino groups with (dicarboxybipyridine)bis(bipyridine)ruthenium (II) were studied by laser flash photolysis. All of the derivatives form complexes with cytochrome c oxidase at low ionic strength (5 mM sodium phosphate, pH 7). Excitation of Ru(II) to Ru(II*) with a short laser flash resulted in rapid electron transfer to the ferric heme group of cytochrome c, followed by electron transfer to cytochrome c oxidase. The photoreduced heme Fe(II) in the cytochrome c derivative modified at lysine 25 on the periphery of the heme crevice domain transferred an electron to CuA with a rate constant of 1.1 x 10(4) s-1. CuA then transferred an electron to cytochrome a with a rate constant of 2.3 x 10(4) s-1. The derivatives modified at lysines 7, 39, 55, and 60 remote from the heme crevice domain of cytochrome c have nearly the same kinetics. The rate constant for electron transfer from the cytochrome c heme to CuA is greater than 10(5) s-1, and the rate constant for electron transfer from CuA to cytochrome a is 2 x 10(4) s-1. The cytochrome c derivatives modified at lysines 13 and 27 in the heme crevice domain react much more slowly than the other derivatives, with intracomplex rate constants for oxidation of cytochrome c ranging from 1000 to 6000 s-1. The bulky ruthenium group at the heme crevice domain of these derivatives apparently alters the binding orientation, leading to smaller electron-transfer rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Could CuB be the site of redox linkage in cytochrome c oxidase?

This paper explores the proton pumping function of cytochrome c oxidase [ferrocytochrome-c:oxygen oxidoreductase (EC 1.9.3.1)] based upon redox linkage at the "high-potential" CuB center. A model is proposed that is derived from a redox-linked ligand exchange mechanism previously described for the CuA site. Qualitative analysis of this mechanism indicates that such a mechanism is feasible. However, the relatively short distance between CuB and cytochrome a3 implies that the uncoupling electron transfers are quite facile. In addition, the position of the CuB center with respect to the inner mitochondrial membrane argues against redox linkage at the CuB site.

The effects of p-hydroxymercuribenzoic acid modification and heat treatment on the CuA reduction potential of cytochrome c oxidase

p-Hydroxymercuribenzoic acid modification of cytochrome c oxidase converts the CuA center into a type 2 copper site while heat treatment of the oxidase in lauryl maltoside can transform CuA almost stoichiometrically (greater than 90%) to a blue type 1 copper site. These modifications of the protein have previously been shown to have a profound effect on the dioxygen reduction and proton pumping activities of the enzyme (Li, P. M., Morgan, J. E., Nilsson, T., Ma, M., and Chan, S. I. (1988) Biochemistry 27, 7538; Nilsson, T., Gelles, J., Li, P. M., and Chan, S. I. (1988) Biochemistry 27, 296; Sone, N., and Nicholls, P. (1984) Biochemistry 23, 6550). In this work, the intrinsic reduction potentials and the midpoint reduction potentials of the "CuA" site in both these modified oxidases have been measured under various conditions in order to clarify the intramolecular electron transfer pathways in these systems. The study reveals that the CuA intrinsic reduction potential decreases by almost 150 mV upon p-hydroxymercuribenzoic acid modification whereas it increases by 100 mV upon heat treatment. In addition, the redox interactions between CuA and the remaining metal centers are perturbed upon CuA modification. It is argued that these results bear on the role of CuA in the proton-pumping paradigm of cytochrome c oxidase.

Trichosanthin, a potent HIV-1 inhibitor, can cleave supercoiled DNA in vitro

Trichosanthin, an abortifacient, immunosuppressive and anti-tumor protein purified from the traditional Chinese herb medicine Tian Hua Fen, is a potent inhibitor against HIV-1 replication. Under normal enzymatic digestion conditions, trichosanthin cleaves the supercoiled double-stranded DNA to produce nicked circular and linear DNA. Trichosanthin has no effect on linear double-stranded DNA. Neither does it convert relaxed circular duplex DNA into a supercoiled form in the presence of ATP. Thus trichosanthin is not a DNA gyrase. However, trichosanthin can cleave the relaxed circular DNA into a linear form, indicating that both the circular as well as the supercoiled forms are essential for trichosanthin recognition. In addition, trichosanthin contains one calcium metal ion per protein molecule, which presumably is related to its endonucleolytic activity.

The nature of zinc in cytochrome c oxidase

The zinc ion in bovine heart cytochrome c oxidase can be completely depleted from the enzyme with mercuric chloride without denaturing the protein. The metal atom stoichiometry of 5Cu/4Fe/0Zn/2Mg obtained for the enzyme following HgCl2 treatment indicates that this depletion is highly selective. Zinc depletion exposes one cysteine on subunit VIa and one cysteine on subunit VIb for N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylene-diamine (1,5-I-AEDANS) labelling, suggesting that the zinc plays a structural role in the protein by providing a bridge between these two subunits. Although the treatment of cytochrome c oxidase with mercuric chloride inhibits the steady-state activity of the enzyme, subsequent removal of the Hg2+ bound to cysteine residues by 1,5-I-AEDANS significantly reverses the inhibition. This latter result indicates that the removal of the zinc itself does not alter the steady-state activity of the enzyme.

The nature of Cux in cytochrome c oxidase

We report here extensive and accurate analyses of the copper, iron, zinc, and magnesium contents in bovine heart cytochrome c oxidase by direct current plasma atomic emission spectrometry. The precision of an individual measurement is within +/- 5%. The analyses confirm a stoichiometry of 5Cu/4Fe/2Zn/2Mg per dimer. Seven enzyme preparations treated by various methods are also analyzed to investigate the nature of Cux. It is shown that Cux is removable by either monomerization of the enzyme or subunit III depletion. This result suggests that Cux is associated with subunit III and that it plays a structural role in enzyme dimerization. EPR measurements indicate that Cux is heterogeneous and mostly reduced. In addition, we find Cux has no effect on the spectroscopic properties and electron transfer activity of the enzyme.

Photoinduced electron transfer within complexes between plastocyanin and ruthenium bisbipyridine dicarboxybipyridine cytochrome c derivatives

A new technique has been developed to measure intracomplex electron transfer between cytochrome c and its redox partners. Cytochrome c derivatives labeled at single lysine amino groups with ruthenium bisbipyridine dicarboxybipyridine were prepared as previously described [Pan, L.P., Durham, B., Wolinska, J., & Millett, F. (1988) Biochemistry 27, 7180-7184]. Excitation of RuII with a short light pulse resulted in the formation of the excited-state RuII*, which rapidly transferred an electron to the ferric heme group to form FeII and RuIII. Aniline was included in the buffer to reduce RuIII to RuII, leaving the heme group in the ferrous state. This process was complete within the lifetime of the light pulse. When plastocyanin was present in the solution, electron transfer from the ferrous heme of cytochrome c to CuII in plastocyanin was observed. All of the ruthenium cytochrome c derivatives formed electrostatic complexes with plastocyanin at low ionic strength, allowing intracomplex electron-transfer rate constants to be measured. The rate constants for derivatives modified at the indicated lysines were as follows: Lys 13, 1920 s-1; Lys 8, 1480 s-1; Lys 7, 1340 s-1; Lys 86, 1020 s-1; Lys 25, 820 s-1; Lys 72, 800 s-1; Lys 27, 530 s-1. It is interesting that the derivative modified at lysine 13 at the top of the heme crevice had the largest rate constant, while lysine 27 at the right side of the heme crevice had the smallest.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoinduced electron-transfer kinetics of singly labeled ruthenium bis(bipyridine) dicarboxybipyridine cytochrome c derivatives

Cytochrome c derivatives labeled at specific lysine amino groups with ruthenium bis(bipyridine) dicarboxybipyridine [RuII(bpy)2(dcbpy)] were prepared by using the procedure described previously [Pan, L. P., Durham, B., Wolinska, J., & Millett, F. (1988) Biochemistry 27, 7180-7184]. Four additional singly labeled derivatives were purified, bringing the total number to 10. These derivatives have a strong luminescence emission centered at 662 nm arising from the excited state, RuII*. Transient absorption spectroscopy was used to directly measure the rate constants for the photoinduced electron-transfer reaction from RuII* to the ferric heme group (k1) and for the thermal back-reaction from the ferrous heme group to RuIII (k2). The rate constants were found to be k1 = 14 X 10(6) s-1 and k2 = 24 X 10(6) s-1 for the derivative modified at lysine 72, which has a distance of 8-16 A between the ruthenium and heme groups. Similar rate constants were found for the derivatives modified at lysines 13 and 27, which have distances of 6-12 A separating the ruthenium and heme groups. The rate constants were significantly slower for the derivatives modified at lysine 25 (k1 = 1 X 10(6) s-1, k2 = 1.5 X 10(6) s-1) and lysine 7 (k1 = 0.3 X 10(6) s-1, k2 = 0.5 X 10(6) s-1), which have distances of 9-16 A. Transients due to photoinduced electron transfer could not be detected for the remaining derivatives, which have larger distances between the ruthenium and heme groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation and characterization of singly labeled ruthenium polypyridine cytochrome c derivatives

A novel two-step procedure has been developed to prepare cytochrome c derivatives labeled at specific lysine amino groups with ruthenium bis(bipyridine) dicarboxybipyridine [RuII(bpy)2(dcbpy)]. In the first step, cytochrome c was treated with the mono-N-hydroxysuccinimide ester of 4,4'-dicarboxy-2,2'-bipyridine (dcbpy) to convert positively charged lysine amino groups to negatively charged dcbpy-lysine groups. Singly labeled dcbpy-cytochrome c derivatives were then separated and purified by ion-exchange chromatography. In the second step, the individual dcbpy-cytochrome c derivatives were treated with RuII(bpy)2CO3 to form singly labeled RuII(bpy)2(dcbpy-cytochrome c) derivatives. The specific lysine labeled in each derivative was determined by reverse-phase chromatography of a tryptic digest. All of the derivatives had a strong luminescence emission centered at 662 nm, but the luminescence decay rates were increased relative to that of a non-heme protein control, RuII(bpy)2(dcbpy-lysozyme), which was 1.8 X 10(6) s-1. The luminescence decay rates were found to be 21, 16, 7.2, 5.7, 4.3, 4.3, and 3.5 X 10(6) s-1 for derivatives singly labeled at lysines 13, 72, 25, 7, 39, 86, and 87, respectively. There was an inverse relationship between the luminescence decay rates and the distances between the ruthenium labels and the heme group. The increased luminescence decay rates observed in the cytochrome c derivatives might be due to electron transfer from the excited triplet state of ruthenium to the ferric heme group. However, it is also possible that an energy-transfer mechanism might contribute to the luminescence quenching.(ABSTRACT TRUNCATED AT 250 WORDS)

Topological studies of monomeric and dimeric cytochrome c oxidase and identification of the copper A site using a fluorescence probe

Beef heart cytochrome c oxidase was labeled at a single sulfhydryl group by treatment with 5 mM N-iodoacetylamidoethyl-1-aminonaphthalene-5-sulfonate (1,5-I-AEDANS) at pH 8.0 for 4 h. Sodium dodecyl sulfate gel electrophoresis revealed that the enzyme was exclusively labeled at subunit III, presumably at Cys-115. The high affinity phase of the electron transfer reaction with horse cytochrome c was not affected by acetylamidoethyl-1-aminonaphthalene-5-sulfonate (AEDANS) labeling. Addition of horse cytochrome c to dimeric AEDANS-cytochrome c oxidase resulted in a 55% decrease in the AEDANS fluorescence due to the formation of a 1:1 complex between the two proteins. Forster energy transfer calculations indicated that the distance from the AEDANS label on subunit III to the heme group of cytochrome c was in the range 26-40 A. In contrast to the results with the dimeric enzyme, the fluorescence of monomeric AEDANS-cytochrome c oxidase was not quenched at all by binding horse heart cytochrome c, indicating that the AEDANS label on subunit III was at least 54 A from the heme group of cytochrome c. These results support a model in which the lysines surrounding the heme crevice of cytochrome c interact with carboxylates on subunit II of one monomer of the cytochrome c oxidase dimer and the back of the molecule is close to subunit III on the other monomer. In order to identify the cysteine residues that ligand copper A, a new procedure was developed to specifically remove copper A from cytochrome c oxidase by incubation with 2-mercaptoethanol followed by gel chromatography. Treatment of the copper A-depleted cytochrome c oxidase preparation with 1,5-I-AEDANS resulted in labeling sulfhydryl groups on subunit II as well as on subunit III. No additional subunits were labeled. This result indicates that the copper A binding site is located at cysteines 196 and/or 200 of subunit II and that removal of copper A exposes these residues for labeling by 1,5-I-AEDANS. Alternative copper A depletion methods involving incubation with bathocuproine sulfonate (Weintraub, S.T., and Wharton, D.C. (1981) J. Biol. Chem. 256, 1669-1676) or p-(hydroxymercuri)benzoate (Li, P.M., Gelles, J., Chan, S.I., Sullivan, R.J., and Scott, R.A. (1987) Biochemistry 26, 2091-2095) were also investigated. Treatment of these preparations with 1,5-I-AEDANS resulted in labeling cysteine residues on subunits II and III. However, additional sulfhydryl residues on other subunits were also labeled, preventing a definitive assignment of the location of copper A using these depletion procedures.

Fluorescein mercuric acetate specifically displaces zinc from cytochrome oxidase

Treatment of beef heart cytochrome oxidase with fluorescein mercuric acetate (FMA) was found to specifically displace zinc from the enzyme and inhibit the steady-state activity in a parallel fashion. The native cytochrome oxidase preparation contained 2.3 Cu: 2.0 Fe: 1.1 Zn: 0.9 Mg. Addition of 2 equivalents of FMA inhibited the activity by 50% and displaced 60% of the zinc from the enzyme, but did not affect the copper, iron or magnesium content. The pre-steady-state reduction of cytochrome oxidase by ferrocytochrome c was not affected by the FMA treatment, in contrast to the inhibition of steady state activity. These results suggest a possible structural or functional role for zinc in cytochrome oxidase.