Survival of multidrug-resistant Salmonella typhimurium DT104 in egg powders as affected by water activity and temperature

A study was done to determine if a four-strain mixture of multidrug-resistant Salmonella typhimurium definitive type 104 (DT104) cells and a four-strain mixture of S. typhimurium non-DT104 cells differed in ability to survive in whole egg powder, whole egg powder supplemented with corn syrup solids (38%) and salt (1.9%), egg yolk powder, and egg white powder as affected by a(w)(0.29-0.37 and 0.51-0.61) during storage at 13 or 37 degrees C for 8 weeks. Rates of inactivation of S. typhimurium DT104 and non-DT104 cells were similar within each set of test parameters. With the exception of whole egg powder supplemented with corn syrup solids and salt, death was enhanced at a(w) 0.29-0.37 compared to a(w) 0.51-0.61 when powders were stored at 13 degrees C. Survival of cells in whole egg powder supplemented with corn syrup solids and salt was significantly (P < or = 0.05) higher compared to survival in other egg powders stored at 13 degrees C. The opposite trend occurred in powders at a(w) 0.5-0.61 stored at 37 degrees C. Survival of S. typhimurium DT104 and non-DT104 cells at initial populations of 5.01-5.39 log10 cfu/g of egg white powder containing 4.9, 6.1, or 8.2% moisture at 54 or 82 degrees C for 7 days or 8 h, respectively, was determined. Rates of inactivation of DT104 and non-DT104 cells did not differ. Both cell types were detected in egg white powder containing 4.9% moisture but not in powder containing 8.2% moisture when held at 54 degrees C for 7 days. Heating at 82 degrees C for 8 h failed to eliminate 5 log10 S. typhimurium per g of egg white powder, regardless of the moisture content.

Systemically administered capsazepine prevents the capsaicin-induced functional desensitization and loss of substance P-like immunoreactivity (SP-LI) in guinea-pig bronchi

In this study, we investigated whether the systemically administered capsazepine can prevent the capsaicin-induced desensitization ex vivo in guinea-pig bronchi. Pretreatment with capsaicin (2.5, 5 and 10 mg/kg, s.c.) induced the functional desensitization and the loss of substance P-like immunoreactivity (SP-LI) with a similar potency (ED50: 3.31 +/- 0.57 and 4.81 +/- 0.89 mg/kg, respectively) in isolated guinea-pig bronchi. Capsazepine (30 mg/kg, s.c.) co-administered with capsaicin (5 mg/kg, s.c.) prevented the capsaicin (5 mg/kg, s.c.)-induced functional desensitization and loss of SP-LI. These results suggest that capsazepine can antagonize systemically the desensitizing action of capsaicin at the level of receptor, preventing the loss of SP-LI and the establishment of functional desensitization in guinea-pig bronchi.

The cysteine-proximal aspartates in the Fx-binding niche of photosystem I. Effect of alanine and lysine replacements on photoautotrophic growth, electron transfer rates, single-turnover flash efficiency, and EPR spectral properties

The FX electron acceptor in Photosystem I (PS I) is a highly electronegative (Em = -705 mV) interpolypeptide [4Fe-4S] cluster ligated by cysteines 556 and 565 on PsaB and cysteines 574 and 583 on PsaA in Synechocystis sp. PCC 6803. An aspartic acid is adjacent to each of these cysteines on PsaB and adjacent to the proline-proximal cysteine on PsaA. We investigated the effect of D566PsaB and D557PsaB on electron transfer through FX by changing each aspartate to the neutral alanine or to the positively charged lysine either singly (D566APsaB, D557APsaB, D566KPsaB, and D557KPsaB) or in pairs (D557APsaB/D566APsaB and D557KPsaB/D566APsaB). All mutants except for D557KPsaB/D566APsaB grew photoautotrophically, but the growth of D557KPsaB and D557APsaB/D566APsaB was impaired under low light. The doubling time was increased, and the chlorophyll content per cell was lower in D557KPsaB and D557APsaB/D566APsaB relative to the wild type and the other mutants. Nevertheless, the rates of NADP+ photoreduction in PS I complexes from all mutants were no less than 75% of that of the wild type. The kinetics of back-reaction of the electron acceptors on a single-turnover flash showed efficient electron transfer to the terminal acceptors FA and FB in PS I complexes from all mutants. The EPR spectrum of FX was identical to that in the wild type in all but the single and double D566APsaB mutants, where the high-field resonance was shifted downfield. We conclude that the impaired growth of some of the mutants is related to a reduced accumulation of PS I rather than to photosynthetic efficiency. The chemical nature and the charge of the amino acids adjacent to the cysteine ligands on PsaB do not appear to be significant factors in the efficiency of electron transfer through FX.

Bioisosterism: interchange of 4-OH to 4-NH2 in vanillin or homovanillin ring of capsaicinoids

A series of 4-amino Capsaicin analogs 15, 17 and 19 were prepared to investigate the bioisosteric effect of 4-amino group, and all these compounds exhibited moderate or weak potency from their analgesic test. From our previous results and others, 4-hydroxyl group as well as 3-methoxy substituent could be crucial for high analgesic activity. This biological result also shows that the activity is sensitive to alkyl chain length in hydrophobic region and the phenylacetic amides 19 are more active than the corresponding urea derivatives 17.

Characterization of angiotensin II antagonism displayed by SK-1080, a novel nonpeptide AT1-receptor antagonist

The pharmacologic profile of SK-1080, a nonpeptide AT1-selective angiotensin-receptor antagonist, was investigated by receptor-binding studies, functional in vitro assays with rabbit and rat aorta, and in vivo experiments in pithed rats. SK-1080 inhibited the specific binding of [125I]-[Sar1, Ile8]-angiotensin II to human recombinant AT1 receptor with a 12-fold greater potency than losartan [median inhibitory concentration (IC50): 1.01 and 12.3 nM, respectively], but it did not inhibit the binding of [125I]-CGP 42112A to human recombinant AT2 receptor (IC50: >10 microM for both). The Hill coefficient for the competition curve of SK-1080 against AT1 receptor was not significantly different from unity (0.96). Scatchard analysis showed that SK-1080 interacted with human recombinant AT1 receptor in a competitive manner, as with losartan. In functional studies with rat and rabbit aorta, SK-1080 competitively inhibited the contractile response to angiotensin II (pKB values: 9.97 and 9.51, respectively) with 15-25% decrease in the maximal contractile responses, unlike losartan, which showed competitive antagonism without any change in the maximal contractile responses to angiotensin II (pA2 values, 8.02 and 7.59, respectively). In pithed rats, SK-1080 (i.v.) induced a nonparallel right shift in the dose-pressor response curve to angiotensin II (ID50, 0.07 mg/kg) with a dose-dependent reduction in the maximal responses; this antagonistic effect was approximately 25 times more potent than losartan (ID50, 1.74 mg/kg), which showed competitive antagonism. SK-1080 did not alter the responses induced by other agonists such as norepinephrine, KCI, and vasopressin in isolated rabbit aorta and pithed rats. These results suggest that SK-1080 is a highly potent AT1-selective angiotensin II-receptor antagonist with a mode of insurmountable antagonism.

Complex formation between Azotobacter vinelandii ferredoxin I and its physiological electron donor NADPH-ferredoxin reductase

In Azotobacter vinelandii, deletion of the fdxA gene, which encodes ferredoxin I (FdI), leads to activation of the expression of the fpr gene, which encodes NADPH-ferredoxin reductase (FPR). In order to investigate the relationship of these two proteins further, the interactions of the two purified proteins have been examined. AvFdI forms a specific 1:1 cross-linked complex with AvFPR through ionic interactions formed between the Lys residues of FPR and Asp/Glu residues of FdI. The Lys in FPR has been identified as Lys258, a residue that forms a salt bridge with one of the phosphate oxygens of FAD in the absence of FdI. UV-Vis and circular dichroism data show that on binding FdI, the spectrum of the FPR flavin is hyperchromatic and red-shifted, confirming the interaction region close to the FAD. Cytochrome c reductase assays and electron paramagnetic resonance data show that electron transfer between the two proteins is pH-dependent and that the [3Fe-4S]+ cluster of FdI is specifically reduced by NADPH via FPR, suggesting that the [3Fe-4S] cluster is near FAD in the complex. To further investigate the FPR:FdI interaction, the electrostatic potentials for each protein were calculated. Strongly negative regions around the [3Fe-4S] cluster of FdI are electrostatically complementary with a strongly positive region overlaying the FAD of FPR, centered on Lys258. These proposed interactions of FdI with FPR are consistent with cross-linking, peptide mapping, spectroscopic, and electron transfer data and strongly support the suggestion that the two proteins are physiological redox partners.

Reduced transforming growth factor-beta type II receptor (TGF-beta RII) expression in adenocarcinoma of the lung

BACKGROUND

TGF-beta type II receptor is considered as one of the tumor suppressor genes, and altered expression of TGF-beta RII has been found in many kinds of cancers.

MATERIALS AND METHODS

Seven NSCLC cell lines and 21 surgically resected NSCLC tissues were obtained. The growth inhibition by TGF-beta 1 was examined by MTT assay. Northern blot and Southern blot analysis were performed for TGF-beta 1 and TGF-beta RII in NSCLC cell lines. TGF-beta 1 and TGF-beta RII expression were analyzed by immunohistochemistry (IHC) in 21 surgically resected NSCLC tissues.

RESULTS

Six of 7 NSCLC cell lines were resistant to TGF-beta 1. Southern blot analysis for TGF-beta 1 and TGF-beta RII showed no genetic changes. However, mRNAs of TGF-beta RII were barely detectable in 3 of 7 cell lines, and mRNAs of TGF-beta 1 were almost undetectable in 2 of 7. IHC revealed decreased TGF-beta RII expression in 6 of 21 surgically resected NSCLC tissues (5 adenocarcinomas, 1 sarcomatoid carcinoma). Being analyzed by the histologic subtypes, TGF-beta RII decreased in 5 of 8 adenocarcinomas but in only 1 of 13 non-adenocarcinomas (p = 0.0139). On the other hand, TGF-beta 1 was expressed at a higher level in 20 of 21 tumors.

CONCLUSION

These results suggest that decreased TGF-beta RII expression may play a role in human lung carcinogenesis, especially in adenocarcinoma.

Capsaicin-induced desensitization is prevented by capsazepine but not by ruthenium red in guinea pig bronchi

In isolated guinea pig bronchi, the influence of ruthenium red, capsazepine and extracellular Ca2+ on capsaicin-induced desensitization was examined to investigate whether this desensitization was mediated via a specific receptor coupled with an ion channel. Pre-exposure of tissues to capsaicin (1, 3 or 10 microM) caused a dose-dependent desensitization to the second application of capsaicin. However, the contractile responses to exogenous tachykinins were not changed after pre-exposure of tissues to capsaicin. This capsaicin-induced desensitization was prevented by capsazepine (30 microM), but not by ruthenium red added to tissues 20 min before pretreatment with capsaicin (3 microM). While the excitatory contractile response to capsaicin was markedly reduced in the absence of extracellular Ca2+, the desensitization induced by capsaicin was not changed by the removal of extracellular Ca2+. In summary, the results from the present study suggest that in vitro functional desensitization induced by capsaicin in guinea pig bronchi may involve changes in the vanilloid receptor and occur through a ruthenium red-insensitive pathway.

The crystal structure of NADPH:ferredoxin reductase from Azotobacter vinelandii

NADPH:ferredoxin reductase (AvFPR) is involved in the response to oxidative stress in Azotobacter vinelandii. The crystal structure of AvFPR has been determined at 2.0 A resolution. The polypeptide fold is homologous with six other oxidoreductases whose structures have been solved including Escherichia coli flavodoxin reductase (EcFldR) and spinach, and Anabaena ferredoxin:NADP+ reductases (FNR). AvFPR is overall most homologous to EcFldR. The structure is comprised of a N-terminal six-stranded antiparallel beta-barrel domain, which binds FAD, and a C-terminal five-stranded parallel beta-sheet domain, which binds NADPH/NADP+ and has a classical nucleotide binding fold. The two domains associate to form a deep cleft where the NADPH and FAD binding sites are juxtaposed. The structure displays sequence conserved motifs in the region surrounding the two dinucleotide binding sites, which are characteristic of the homologous enzymes. The folded over conformation of FAD in AvFPR is similar to that in EcFldR due to stacking of Phe255 on the adenine ring of FAD, but it differs from that in the FNR enzymes, which lack a homologous aromatic residue. The structure of AvFPR displays three unique features in the environment of the bound FAD. Two features may affect the rate of reduction of FAD: the absence of an aromatic residue stacked on the isoalloxazine ring in the NADPH binding site; and the interaction of a carbonyl group with N10 of the flavin. Both of these features are due to the substitution of a conserved C-terminal tyrosine residue with alanine (Ala254) in AvFPR. An additional unique feature may affect the interaction of AvFPR with its redox partner ferredoxin I (FdI). This is the extension of the C-terminus by three residues relative to EcFldR and by four residues relative to FNR. The C-terminal residue, Lys258, interacts with the AMP phosphate of FAD. Consequently, both phosphate groups are paired with a basic group due to the simultaneous interaction of the FMN phosphate with Arg51 in a conserved FAD binding motif. The fourth feature, common to homologous oxidoreductases, is a concentration of 10 basic residues on the face of the protein surrounding the active site, in addition to Arg51 and Lys258.

Pharmacokinetics of losartan and its metabolite, EXP3174, after intravenous and oral administration of losartan to rats with streptozotocin-induced diabetes mellitus

The pharmacokinetics of losartan and its active metabolite, EXP3174, were investigated after intravenous and oral administration of the drug, 5 mg/kg, to control rats and streptozotocin-induced diabetes mellitus rats (SIDRs). After 1-min intravenous infusion, the mean arterial plasma concentrations and the resultant area under the plasma concentration-time curve from zero to infinity (AUC) of both losartan and EXP3174 were not significantly different between control rats and the SIDRs. However, the renal clearance (CLR) of losartan (0.181 versus 0.0815 ml/min/kg) and EXP3174 (0.0677 versus 0.0277 ml/min/kg) were significantly faster in SIDRs than in control rats due to significant increase in glomerular filtration rate. After oral administration, the mean arterial plasma concentrations and the resultant AUC of losartan (97 versus 166 micrograms min/ml) and EXP3174 (244 versus 423 micrograms min/ml) were significantly lower in SIDRs than in control rats. The absolute extent of oral bioavailability of losartan, F, (32.5 versus 55.1%) decreased considerably in SIDRs and it was possibly due to the reduced gastrointestinal absorption of losartan by gastrointestinal disorders occurring in the diabetic state. The low F in both groups of rats was at least partially due to the increase in first-pass effects. The CLR of losartan (0.207 versus 0.101 ml/min/kg) and EXP3174 (0.0615 versus 0.0196 ml/min/kg) were significantly faster in SIDRs than in control rats after oral administration of losartan.

PsaC subunit of photosystem I is oriented with iron-sulfur cluster F(B) as the immediate electron donor to ferredoxin and flavodoxin

The PsaC subunit of photosystem I (PS I) binds two [4Fe-4S] clusters, F(A) and F(B), functioning as electron carriers between F(X) and soluble ferredoxin. To resolve the issue whether F(A) or F(B) is proximal to F(X), we used single-turnover flashes to promote step-by-step electron transfer between electron carriers in control (both F(A) and F(B) present) and HgCl2-treated (F(B)-less) PS I complexes from Synechococcus sp. PCC 6301 and analyzed the kinetics of P700+ reduction by monitoring the absorbance changes at 832 nm in the presence of a fast electron donor (phenazine methosulfate (PMS)). In control PS I complexes exogenously added ferredoxin, or flavodoxin could be photoreduced on each flash, thus allowing P700+ to be reduced from PMS. In F(B)-less complexes, both in the presence and in the absence of ferredoxin or flavodoxin, P700+ was reduced from PMS only on the first flash and was reduced from F(X)- on the following flashes, indicating lack of electron transfer to ferredoxin or flavodoxin. In the F(B)-less complexes, a normal level of P700 photooxidation was detected accompanied by a high yield of charge recombination between P700+ and F(A)- in the presence of a slow donor, 2,6-dichlorophenol-indophenol. This recombination remained the only pathway of F(A)- reoxidation in the presence of added ferredoxin, consistent with the lack of forward electron transfer. F(A)- could be reoxidized by methyl viologen in F(B)-less PS I complexes, although at a concentration two orders of magnitude higher than is required in wild-type PS I complexes, thus implying the presence of a diffusion barrier. The inhibition of electron transfer to ferredoxin and flavodoxin was completely reversed after reconstituting the F(B) cluster. Using rate versus distance estimates for electron transfer rates from F(X) to ferredoxin for two possible orientations of PsaC, we conclude that the kinetic data are best compatible with PsaC being oriented with F(A) as the cluster proximal to F(X) and F(B) as the distal cluster that donates electrons to ferredoxin.

Cardioprotective effects of KR-30450, a novel K+(ATP) opener, and its major metabolite KR-30818 on isolated rat hearts

The cardiac effects of KR-30450 ((-)-(2R)-2-([1,3]-dioxolan-2-yl)-2-methyl-4-(2-oxopyrrolidin++ +-1-yl)-6-nitro-2H-1-benzopyran), a newly synthesized potassium channel activator, and its major metabolite KR-30818 ((-)-(2R)-2-hydroxymethyl-2-methyl-4-(2-oxopyrrolidin-1-yl)-6-nitr o-2H-1-benzopyran) were compared with those of lemakalim, a prototype of this class, in isolated globally ischemic rat hearts. KR-30450 and KR-30818 significantly improved reperfusion cardiac function (LVDP, left ventricular developed pressure; double product, LVDP x heart rate/1000), their potency being 5.2-fold and 0.7-fold greater than lemakalim (ED50 for recovering predrug double product: 0.10, 0.80 and 0.54 microM, respectively). KR-30450 and KR-30818 significantly attenuated reperfusion contracture and lactate dehydrogenase release with potency greater than and equal to lemakalim, respectively. They significantly increased time to contracture (TTC) during ischemia in a dose-dependent manner with a greater potency than lemakalim (EC25 for increasing TTC: 1.2, 2.1 and 3.2 microM, respectively). The protective effects of three compounds on the measured parameters were reversed by glyburide, a selective K+(ATP) blocker. In non-ischemic hearts, KR-30450 and lemakalim exerted weak negative inotropism at high concentrations and KR-30818 had no effects, whereas the three compounds significantly increased coronary flow at doses studied. Glyburide completely reversed preischemic cardiodepressant effects of these compounds but not their effects on coronary flow. In conclusion, KR-30450, a recently developed K+(ATP) opener, exerted more potent cardioprotective effects than lemakalim, and its major metabolite KR-30818 may play a significant role in its action in vivo.

Strains of synechocystis sp. PCC 6803 with altered PsaC. I. Mutations incorporated in the cysteine ligands of the two [4Fe-4S] clusters FA and FB of photosystem I

Two [4Fe-4S] clusters, FA and FB, function as terminal electron carriers in Photosystem I (PS I), a thylakoid membrane-bound protein-pigment complex. To probe the function of these two clusters in photosynthetic electron transport, site-directed mutants were created in the transformable cyanobacterium Synechocystis sp. PCC 6803. Cysteine ligands in positions 14 or 51 to FB and FA, respectively, were replaced with aspartate, serine, or alanine, and the effect on the genetic, physiological, and biochemical characteristics of PS I complexes from the mutant strains were studied. All mutant strains were unable to grow photoautotrophically, and compared with wild type, mixotrophic growth was inhibited under normal light intensity. The mutant cells supported lower rates of whole-chain photosynthetic electron transport. Thylakoids isolated from the aspartate and serine mutants have lower levels of PS I subunits PsaC, PsaD, and PsaE and lower rates of PS I-mediated substrate photoreduction compared with the wild type. The alanine and double aspartate mutants have no detectable levels PsaC, PsaD, and PsaE. Electron transfer rates, measured by cytochrome c6-mediated NADP+ photoreduction, were lower in purified PS I complexes from the aspartate and serine mutants. By measuring the P700(+) kinetics after a single turnover flash, a large percentage of the backreaction in the aspartate and serine mutants was found to be derived from A1 and FX, indicating an inefficiency at the FX --> FA/FB electron transfer step. The alanine and double aspartate mutants failed to show any backreaction from [FA/FB]-. These results indicate that the various mutations of the cysteine 14 and 51 ligands to FB and FA affect biogenesis and electron transfer differently depending on the type of substitution, and that the effects of mutations on biogenesis and function can be biochemically separated and analyzed.

Strains of Synechocystis sp. PCC 6803 with altered PsaC. II. EPR and optical spectroscopic properties of FA and FB in aspartate, serine, and alanine replacements of cysteines 14 and 51

A psaC deletion mutant of the unicellular cyanobacterium Synechocystis sp. PCC 6803 was utilized to incorporate site-specific amino acid substitutions in the cysteine residues that ligate the FA and FB iron-sulfur clusters in Photosystem I (PS I). Cysteines 14 and 51 of PsaC were changed to aspartic acid (C14DPsaC, C51DPsaC, C14D/C51DPsaC), serine (C14SPsaC, C51SPsaC), and alanine (C14APsaC, C51APsaC), and the properties of FA and FB were characterized by electron paramagnetic resonance spectroscopy and time-resolved optical spectroscopy. The C14DPsaC-PS I and C14SPsaC-PS I complexes showed high levels of photoreduction of FA with g values of 2.045, 1. 944, and 1.852 after illumination at 15 K, but there was no evidence of reduced FB in the g = 2 region. The C51DPsaC-PS I and C51SPsaC-PS I complexes showed low levels of photoreduction of FB with g values of 2.067, 1.931, and 1.881 after illumination at 15 K, but there was no evidence of reduced FA in the g = 2 region. The presence of FB was inferred in C14DPsaC-PS I and C14SPsaC-PS I, and the presence of FA was inferred in C51DPsaC-PS I and C51SPsaC-PS I by magnetic interaction in the photoaccumulated spectra and by the equal spin concentration of the irreversible P700(+) cation generated by illumination at 77 K. Flash-induced optical absorbance changes at 298 K in the presence of a fast electron donor indicate that two electron acceptors function after FX in the four mutant PS I complexes at room temperature. These data suggest that a mixed-ligand [4Fe-4S] cluster is present in the mutant sites of C14X-PS I and C51X-PS I (where X = D or S), but that the proposed spin state of S = 3/2 renders the resonances undetectable in the g = 2 region. The C14APsaC-PS I, C51APsaC-PS I and C14D/C51DPsaC-PS I complexes show only the photoreduction of FX, consistent with the absence of PsaC. These results show that only those PsaC proteins that contain two [4Fe-4S] clusters are capable of assembling onto PS I cores in vivo.

Near-IR absorbance changes and electrogenic reactions in the microsecond-to-second time domain in Photosystem I

The back-reaction kinetics in Photosystem I (PS I) were studied on the microsecond-to-s time scale in cyanobacterial preparations, which differed in the number of iron-sulfur clusters to assess the contributions of particular components to the reduction of P700+. In membrane fragments and in trimeric P700-FA/FB complexes, the major contribution to the absorbance change at 820 nm (delta A820) was the back-reaction of FA- and/or FB- with lifetimes of approximately 10 and 80 ms (approximately 10% and 40% relative amplitude). The decay of photoinduced electric potential (delta psi) across a membrane with directionally incorporated P700-FA/FB complexes had similar kinetics. HgCl2-treated PS I complexes, which contain FA but no FB, retain both of these kinetic components, indicating that neither can be assigned uniquely to a specific acceptor. These results suggest that FA- reduces P700+ directly and argue for a rapid electron equilibration between FA and FB, which would eliminate their kinetic distinction in a back-reaction. In PsaC-depleted P700-Fx cores, as well as in P700-FA/FB complexes with chemically reduced FA and FB, the major contribution to the delta A820 and the delta psi decay is a biphasic back-reaction of F-X (approximately 400 microseconds and 1.5 ms) with some contribution from A-1 (approximately 10 microseconds and 100 microseconds), the latter of which is variable depending on experimental conditions. The delta A820 decay in a P700-A1 core devoid of all iron-sulfur clusters comprises two phases with lifetimes of 10 microseconds and 130 microseconds (2.7:1 ratio). The biexponential back-reaction kinetics found for each of the electron acceptors may be related to existence of different conformational states of the PS I complex. In all preparations studied, excitation at 532 nm with flash energies exceeding 10 mJ gives rise to formation of antenna 3Chl, which also contributes to delta A820 decay on the tens-of-microsecond time scale. A distinction between delta A820 components related to back-reactions and to 3Chl decay can be made by analysis of flash saturation dependencies and by measurements of kinetics with preoxidized P700.

Modified ligands to FA and FB in photosystem I. Proposed chemical rescue of a [4Fe-4S] cluster with an external thiolate in alanine, glycine, and serine mutants of PsaC

The FB and FA electron acceptors in Photosystem I (PS I) are [4Fe-4S] clusters ligated by cysteines provided by PsaC. In a previous study (Mehari, T., Qiao, F., Scott, M. P., Nellis, D., Zhao, J., Bryant, D., and Golbeck, J. H. (1995) J. Biol. Chem. 270, 28108-28117), we showed that when cysteines 14 and 51 were replaced with serine or alanine, the free proteins contained a S = 1/2, [4Fe-4S] cluster at the unmodified site and a mixed population of S = 1/2, [3Fe-4S] and S = 3/2, [4Fe-4S] clusters at the modified site. We show here that these mutant PsaC proteins can be rebound to P700-FX cores, resulting in fully functional PS I complexes. The low temperature EPR spectra of the C14XPsaC.PS I complexes (where X = S, A, or G) show the photoreduction of a wild-type FA cluster and a modified FB' cluster, the latter with g values of 2.115, 1.899, and 1.852 and linewidths of 110, 70, and 85 MHz. Since neither alanine nor glycine contains a suitable side group, an external thiolate provided by beta-mercaptoethanol has likely been recruited to supply the requisite ligand to the [4Fe-4S] cluster. The EPR spectrum of the C51SPsaC.PS I complex differs from that of the C51APsaC.PS I or C51GPsaC.PS I complexes by the presence of an additional set of resonances, which may be derived from the serine oxygen-ligated cluster. In all other mutant PS I complexes, a wild-type spin-coupled interaction spectrum appears when FA and FB are simultaneously reduced. Single turnover flash studies indicate approximately 50% efficient electron transfer to FA/FB in the C14SPsaC.PS I, C51SPsaC.PS I, C14GPsaC.PS I, and C51GPsaC.PS I mutants and less than 40% in the C14APsaC.PS I and C51APsaC.PS I mutants, compared with approximately 76% in the PS I core reconstructed with wild-type PsaC. These data are consistent with the measurements of the rates of cytochrome c6-NADP+ reductase activity, indicating lower rates in the alanine mutants. It is proposed that the chemical rescue of a [4Fe-4S] cluster with a recruited external thiolate at the modified site allows the mutant PsaC proteins to rebind to PS I and to function in forward electron transfer.

Modified ligands to FA and FB in photosystem I. II. Characterization of a mixed ligand [4Fe-4S] cluster in the C51D mutant of PsaC upon rebinding to P700-Fx cores

A Photosystem I (PS I) complex reconstituted with PsaC-C51D (aspartate in lieu of cysteine in position 51) shows light-induced EPR signals with g values, line widths, and photoreduction behavior characteristic of FB. Contrary to an earlier report, a [3Fe-4S] cluster was not located in the reconstituted PS I complex. Instead, a second set of resonances with g values of 2.044, 1.942, and 1.853 becomes EPR-visible when the C51D-PS I complex is measured at 4.2 K. This fast relaxing center, termed FA' is likely to represent a [4Fe-4S] cluster in the mixed ligand (3Cys.1Asp) site. Redox studies show that the Em of FA' and FB are -630 mV and -575 mV, respectively. Room temperature optical studies support the presence of two functioning electron acceptors subsequent to Fx, and NADP+ photoreduction rates mediated by ferredoxin and flavodoxin are nearly equivalent to the wild type. In addition to [3Fe-4S] clusters and S = 1/2 ground state [4Fe-4S] clusters, the free PsaC-C51D protein shows resonances near g = 5.5, which may represent a population of high spin (S = 3/2) [4Fe-4S] clusters in the mixed ligand FA' site. Similar to the C14D-PS I mutant complex, it is proposed that the P700-Fx core selectively rebinds those free PsaC-C51D proteins that contain two [4Fe-4S] clusters. These studies show that primary photochemistry and electron transfer rates in PS I are relatively unaffected by the presence of a highly reducing, mixed ligand cluster in the FA' site.

Reversed-phase high-performance liquid chromatography of salmon calcitonin and its degradation products in biological samples using column switching and flow-through radioisotope detection

For the determination of salmon calcitonin and its degradation products in biological samples, a reversed-phase HPLC method with column switching and flow-through radioisotope detection has been developed using high specific activity [125I]salmon calcitonin. Effects of the precolumn packing material and washing solvent were examined in terms of [125I]salmon calcitonin recovery. Spiked samples of [125I]salmon calcitonin in plasma and kidney homogenate were injected onto a LiChroprep RP-8 precolumn after dilution with 0.1% trifluoroacetic acid. After washing the polar interfering compounds with 0.1% trifluoroacetic acid, the concentrated [125I]salmon calcitonin and its degradation products were eluted and separated on a W-Porex C18 column with a gradient of 0.1% trifluoroacetic acid in acetonitrile-water. Detection and calibration of [125I]salmon calcitonin were possible down to picogram levels. Reproducible kinetic data for the degradation of intact [125I]salmon calcitonin were possible down to picogram levels. Reproducible kinetic data for the degradation of intact [125I]salmon calcitonin by rat kidney homogenate could be traced.

Reconstitution of iron-sulfur center FB results in complete restoration of NADP (+) photoreduction in Hg-treated Photosystem I complexes from Synechococcus sp. PCC 6301

The FB iron-sulfur cluster is destroyed preferentially by treating Photosystem I complexes with HgCl2(Kojima Y, Niinomi Y, Tsuboi S, Hiyama T and Sakurai H (1987) Bot Mag 100: 243-53). When FB is 95% depleted but FAis quantitatively retained in cyanobacterial PS I complexes, the reduction potential of FA remains highly electronegative (Em=-530 mV, n=1), the EPR spectral and spin relaxation properties of FA and FXremain unchanged, but NADP(+) photoreduction rates decline from 552 to 72 μmol mg Chl(-1) h(-1).When FB is reconstituted with FeCl3, Na2S and β-mercaptoethanol, NADP(+)photoreduction rates recover to 528 μmol mg Chl(-1) h(-1). The correlation between the presence of FBand NADP(+) photoreduction provides direct experimental evidence that this iron-sulfur cluster is required for electron throughput from cytochromec 6 to flavodoxin or ferredoxin in Photosystem I.

Absence of PsaC subunit allows assembly of photosystem I core but prevents the binding of PsaD and PsaE in Synechocystis sp. PCC6803

In photosystem I (PSI) of oxygenic photosynthetic organisms the psaC polypeptide, encoded by the psaC gene, provides the ligands for two [4Fe-4S] clusters, FA and FB. Unlike other cyanobacteria, two different psaC genes have been reported in the cyanobacterium Synechocystis 6803, one (copy 1) with a deduced amino acid sequence identical to that of tobacco and another (copy 2) with a deduced amino acid sequence similar to those reported for other cyanobacteria. Insertion of a gene encoding kanamycin resistance into copy 2 resulted in a photosynthesis-deficient strain, CDK25, lacking the PsaC, PsaD and PsaE polypeptides in isolated thylakoid membranes, while the PsaA/PsaB and PsaF subunits were found. Growth of the mutant cells was indistinguishable from that of wild-type cells under light-activated heterotrophic growth (LAHG). A reversible P700+ signal was detected by EPR spectroscopy in the isolated thylakoids during illumination at low temperature. Under these conditions, the EPR signals attributed to FA and FB were absent in the mutant strain, but a reversible Fx signal was present with broad resonances at g = 2.079, 1.903, and 1.784. Addition of PsaC and PsaD proteins to the thylakoids gave rise to resonances at g = 2.046, 1.936, 1.922, and 1.880; these values are characteristic of an interaction-type spectrum of FA- and FB-. In room-temperature optical spectroscopic analysis, addition of PsaC and PsaD to the thylakoids also restored a 30 ms kinetic transient which is characteristic of the P700+ [FA/FB]- backreaction. Expression of copy 1 was not detected in cells grown under LAHG and under mixotrophic conditions. These results demonstrate that copy 2 encodes the PsaC polypeptide in PSI in Synechocystis 6803, while copy 1 is not involved in PSI; that the PsaC polypeptide is necessary for stable assembly of PsaD and PsaE into PSI complex in vivo; and that PsaC, PsaD and PsaE are not needed for assembly of PsaA-PsaB dimer and electron transport from P700 to Fx.

A mixed-ligand iron-sulfur cluster (C556SPaB or C565SPsaB) in the Fx-binding site leads to a decreased quantum efficiency of electron transfer in photosystem I

The proposed structure of Photosystem I depicts two cysteines on the PsaA polypeptide and two cysteines on the PsaB polypeptide in a symmetrical environment, each providing ligands for the interpolypeptide Fx cluster. We studied the role of Fx in electron transfer by substituting serine for cysteine (C565SPsaB and C556SPsaB), thereby introducing the first example of a genetically engineered, mixed-ligand [4Fe-4S] cluster into a protein. Optical kinetic spectroscopy shows that after a single-turnover flash at 298 K, the contribution of A1- (lifetime of 10 microseconds, 40% of total and lifetime of 100 microseconds, 20% of total) and Fx- (lifetime of 500-800 microseconds, 10-15% of total) to the overall P700+ back reaction have increased in C565SPsaB and C556SPsaB at the expense of the back reaction from [FA/FB]-. The electron paramagnetic resonance spectrum of Fx shows g-values of 2.04, 1.94, and 1.81 in both mutants and a similarly decreased amount of FA and FB reduced at 15 K after a single-turnover flash. These results indicate that the mixed-ligand (3 cysteines, 1 serine) Fx cluster is an inefficient electron carrier, but that a small leak through Fx still permits FA and FB to be reduced quantitatively when the samples are frozen during continuous illumination. The data confirm that Fx is a necessary intermediate in the electron transfer pathway from A1 to FA and FB in Photosystem I.

Location of the catalytic site for phosphoenolpyruvate formation within the primary structure of Clostridium symbiosum pyruvate phosphate dikinase. 1. Identification of an essential cysteine by chemical modification with [1-14C]bromopyruvate and site-directed mutagenesis

Pyruvate phosphate dikinase (PPDK) catalyzes the interconversion of adenosine 5'-triphosphate (ATP), orthophosphate (Pi), and pyruvate with adenosine 5'-monophosphate (AMP), pyrophosphate (PPi), and phosphoenolpyruvate (PEP). The reaction takes place according to the following steps: (1) E+ATP+P(i)<-->E-PP.AMP.P(i), (2) E-PP.AMP.P(i)<-->E-P+AMP+PP(i), and (3) E-P+pyruvate<-->E+PEP, where E represents free enzyme; E-PP, pyrophosphorylenzyme; and E-P, phosphorylenzyme. Steps 1 and 2 comprise the nucleotide partial reaction, and step 3 comprises the pyruvate partial reaction. The present studies were carried out to locate amino acid residues within the primary structure of Clostridium symbiosum PPDK participating in the catalysis of the pyruvate partial reaction. The enzyme was treated with the affinity label [1-14C]bromopyruvate, reduced with NaBH4, proteolyzed with trypsin, and chromatographed on an HPLC column. The radiolabeled tryptic peptide isolate was sequenced to reveal Cys 831 as the site of alkylation. Using PCR techniques Cys 831 was replaced by Ala, and the C831A PPDK mutant formed was then subjected to kinetic analysis. Rapid quench studies of single turnover reactions on the enzyme showed that the mutant is as efficient as wild-type PPDK in catalyzing the nucleotide partial reaction while it is unable to catalyze the pyruvate partial reaction. These results were interpreted as evidence for a role of Cys 831 in pyruvate/PEP binding and/or catalysis.

Mutational analysis of photosystem I polypeptides in Synechocystis sp. PCC 6803. Subunit requirements for reduction of NADP+ mediated by ferredoxin and flavodoxin

The subunit requirements for NADP+ reduction by photosystem I were assessed in mutants of Synechocystis sp. PCC 6803 created by targeted inactivation of the psaD, psaE, psaF, and psaL genes. The PsaE-less, PsaF-PsaJ-less, and PsaL-less mutants showed normal photoautotrophic growth, while the growth of PsaD-less mutants was slower without glucose. In isolated wild-type membranes, the rate of flavodoxin reduction and flavodoxin-mediated NADP+ reduction were 800 and 480 mumol/mg of chlorophyll/h, respectively. The rate of ferredoxin-mediated NADP+ photoreduction was 460 mumol/mg of chlorophyll/h. There was no diminution in NADP+ photoreduction in membranes isolated from the PsaF-less and PsaL-less mutants. The rates of ferredoxin-mediated NADP+ photoreduction in membranes of the PsaE-less mutants were 25 mumol/mg of chlorophyll/h. However, the rate of flavodoxin reduction was 380 mumol/mg of chlorophyll/h, and that of flavodoxin-mediated NADP+ photoreduction was 170 mumol/mg of chlorophyll/h. PsaD-less membranes showed < 20% of the wild-type rates of flavodoxin-mediated NADP+ photoreduction, but were completely deficient in ferredoxin-mediated NADP+ photoreduction. Therefore, the roles of PsaE and PsaD are more crucial for "docking" of ferredoxin than of flavodoxin. Proteolysis studies showed that while PsaD was susceptible to rapid in vitro degradation by thermolysin, the number and sizes of protease-resistant fragments were not affected by the absence of PsaE. Protease accessibility studies further indicated that the C-terminal domain of PsaD is surface-exposed on the n-side. These results suggest that PsaE and the C-terminal domain of PsaD generate the docking site for the electron acceptors of photosystem I.

Iron-sulfur centers in the photosynthetic reaction center complex fromChlorobium vibrioforme. Differences from and similarities to the iron-sulfur centers in Photosystem I

The photosynthetic reaction center complex from the green sulfur bacteriumChlorobium vibrioforme has been isolated under anaerobic conditions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals polypeptides with apparent molecular masses of 80, 40, 30, 18, 15, and 9 kDa. The 80- and 18-kDa polypeptides are identified as the reaction center polypeptide and the secondary donor cytochromec 551 encoded by thepscA andpscC genes, respectively. N-terminal amino acid sequences identify the 40-kDa polypeptide as the bacteriochlorophylla-protein of the baseplate (the Fenna-Matthews-Olson protein) and the 30-kDa polypeptide as the putative 2[4Fe-4S] protein encoded bypscB. Electron paramagnetic resonance (EPR) analysis shows the presence of an iron-sulfur cluster which is irreversibly photoreduced at 9K. Photoaccumulation at higher temperature shows the presence of an additional photoreduced cluster. The EPR spectra of the two iron-sulfur clusters resemble those of FA and FB of Photosystem I, but also show significantly differentg-values, lineshapes, and temperature and power dependencies. We suggest that the two centers are designated Center I (with calculatedg-values of 2.085, 1.898, 1.841), and Center II (with calculatedg-values of 2.083, 1.941, 1.878). The data suggest that Centers I and II are bound to thepscB polypeptide.

An empirical literature review of definitions of severe and persistent mental illness

Seventeen definitions of the severely and persistently mentally ill have appeared in the literature over the past decade. These definitions have been used by 13 authors to formulate service programs and to estimate the prevalence of serious mental illness in the population. To test the applicability of these definitions, the authors operationalized each definition and applied it to a representative sample of 222 patients receiving services in one of Philadelphia's inner-city neighborhoods. The analysis showed estimates of prevalence of serious mental illness ranging from 4% to 88% of the treated population, depending on the definition applied. The NIMH (1987) definition was representative of the middle-range estimates of 45% to 55% arrived at by eight authors.

[Case report of the Sturge-Weber syndrome with intraoral finding]

The authors observed a 20-year-old female patient who had come to Department of Dentistry, Kyungpook National University Hospital due to the chief complaints of gingival enlargement and pain on the upper jaw. We performed the clinical, hematologic and radiologic examinations for the patient and obtained the following results; 1. We observed a nevus flammeus on the right side of the facial area, soft palate and buccal mucosa. 2. The enlargement of the upper and lower gingiva, we thought, was due to inflammatory reaction. 3. The above clinical signs were found in accordance with the maxillary and ophthalmic branch of trigeminal nerve. 4. The maxillary sinus was enlarged in Water's view. 5. Finally, we have reached the diagnosis of Sturge-Weber syndrome for the patient.