Rational reprogramming of the R2 subunit of Escherichia coli ribonucleotide reductase into a self-hydroxylating monooxygenase

The outcome of O2 activation at the diiron(II) cluster in the R2 subunit of Escherichia coli (class I) ribonucleotide reductase has been rationally altered from the normal tyrosyl radical (Y122*) production to self-hydroxylation of a phenylalanine side-chain by two amino acid substitutions that leave intact the (histidine)2-(carboxylate)4 ligand set characteristic of the diiron-carboxylate family. Iron ligand Asp (D) 84 was replaced with Glu (E), the amino acid found in the cognate position of the structurally similar diiron-carboxylate protein, methane monooxygenase hydroxylase (MMOH). We previously showed that this substitution allows accumulation of a mu-1,2-peroxodiiron(III) intermediate, which does not accumulate in the wild-type (wt) protein and is probably a structural homologue of intermediate P (H(peroxo)) in O2 activation by MMOH. In addition, the near-surface residue Trp (W) 48 was replaced with Phe (F), blocking transfer of the "extra" electron that occurs in wt R2 during formation of the formally Fe(III)Fe(IV) cluster X. Decay of the mu-1,2-peroxodiiron(III) complex in R2-W48F/D84E gives an initial brown product, which contains very little Y122* and which converts very slowly (t1/2 approximately 7 h) upon incubation at 0 degrees C to an intensely purple final product. X-ray crystallographic analysis of the purple product indicates that F208 has undergone epsilon-hydroxylation and the resulting phenol has shifted significantly to become a ligand to Fe2 of the diiron cluster. Resonance Raman (RR) spectra of the purple product generated with 16O2 or 18O2 show appropriate isotopic sensitivity in bands assigned to O-phenyl and Fe-O-phenyl vibrational modes, confirming that the oxygen of the Fe(III)-phenolate species is derived from O2. Chemical analysis, experiments involving interception of the hydroxylating intermediate with exogenous reductant, and Mössbauer and EXAFS characterization of the brown and purple species establish that F208 hydroxylation occurs during decay of the peroxo complex and formation of the initial brown product. The slow transition to the purple Fe(III)-phenolate species is ascribed to a ligand rearrangement in which mu-O2- is lost and the F208-derived phenolate coordinates. The reprogramming to F208 monooxygenase requires both amino acid substitutions, as very little epsilon-hydroxyphenylalanine is formed and pathways leading to Y122* formation predominate in both R2-D84E and R2-W48F.

Enrichment media for isolation of Campylobacter jejuni from inoculated ground beef and chicken skin under normal atmosphere

The efficiency of Hunt broth containing Oxyrase was compared with the gas replacement method for detection of Campylobacter jejuni in inoculated ground beef and chicken skin. Five strains of C. jejuni were inoculated individually into samples and cultured with various media under conditions generated by either flushing with a mixture of gases or supplementing with Oxyrase. Oxyrase media added with 7% lysed blood, 2.5% charcoal, or 6% ground cooked meat were compared with examinations from chicken skin samples. Campylobacter counts from enrichments were performed at 6, 12, 20, and 28 h of incubation. From inoculated ground beef, counts at 20 h increased by 4 to 7 log CFU/ml depending on strains and initial concentration of inocula. The efficiencies of Hunt medium using gassing and those with Oxyrase added were similar (P > 0.05). Broth containing 0.15 U/ml of Oxyrase without blood effectively supported the growth of all strains (P > 0.05). From inoculated chicken skin, 20-h incubation counts increased by 3.0 to 7.5 log CFU/ml for the gassing method and by 2.7 to 7.3 log CFU/ml for supplementation with 0.6 U/ml of Oxyrase and blood. The addition of 7% lysed sheep blood provided better Campylobacter growth than supplementing with 2.5% charcoal or 6% ground cooked meat. Enrichment media incorporating with Oxyrase is a simple, convenient, and time-saving method to replace flushing with mixed gas for isolation of Campylobacter jejuni.

Flavohemoglobin, a globin with a peroxidase-like catalytic site

Biochemical studies of flavohemoglobin (Hmp) from Escherichia coli suggest that instead of aerobic oxygen delivery, a dioxygenase converts NO to NO3(-) and anaerobically, an NO reductase converts NO to N(2)O. To investigate the structural features underlying the chemical reactivity of Hmp, we have measured the resonance Raman spectra of the ligand-free ferric and ferrous protein and the CO derivatives of the ferrous protein. At neutral pH, the ferric protein has a five-coordinate high-spin heme, similar to peroxidases. In the ferrous protein, a strong iron-histidine stretching mode is present at 244 cm(-1). This frequency is much higher than that of any other globin discovered to date, although it is comparable to those of peroxidases, suggesting that the proximal histidine has imidazolate character. In the CO derivative, an open and a closed conformation were detected. The distal environment of the closed conformation is very polar, where the heme-bound CO strongly interacts with the B10 Tyr and/or the E7 Gln. These data demonstrate that the active site structure of Hmp is very similar to that of peroxidases and is tailored to perform oxygen chemistry.

ihfA gene of the bacterium Myxococcus xanthus and its role in activation of carotenoid genes by blue light

Myxococcus xanthus responds to blue light by producing carotenoids. Several regulatory genes are known that participate in the light action mechanism, which leads to the transcriptional activation of the carotenoid genes. We had already reported the isolation of a carotenoid-less, Tn5-induced strain (MR508), whose mutant site was unlinked to the indicated regulatory genes. Here, we show that OmegaMR508::Tn5 affects all known light-inducible promoters in different ways. It blocks the activation of two of them by light but makes the activity of a third one light independent. The OmegaMR508 locus has been cloned and sequenced. The mutation had occurred at the promoter of a gene we propose is the M. xanthus ortholog of ihfA. This encodes the alpha subunit of the histone-like integration host factor protein. An in-frame deletion within ihfA causes the same effects as the OmegaMR508::Tn5 insertion. Like other IhfA proteins, the deduced amino acid sequence of M. xanthus IhfA shows much similarity to HU, another histone-like protein. Sequence comparison data, however, and the finding that the M. xanthus gene is preceded by gene pheT, as happens in other gram-negative bacteria, strongly argue for the proposed orthology relationship. The M. xanthus ihfA gene shows some unusual features, both from structural and physiological points of view. In particular, the protein is predicted to have a unique, long acidic extension at the carboxyl terminus, and it appears to be necessary for normal cell growth and even vital for a certain wild-type strain of M. xanthus.

Effects of batroxobin on spatial learning and memory disorder of rats with temporal ischemia and the expression of HSP32 and HSP70

The effect of Batroxobin on spatial memory disorder of left temporal ischemic rats and the expression of HSP32 and HSP70 were investigated with Morri's water maze and immunohistochemistry methods. The results showed that the mean reaction time and distance of temporal ischemic rats in searching a goal were significantly longer than those of the sham-operated rats and at the same time HSP32 and HSP70 expression of left temporal ischemic region in rats was significantly increased as compared with the sham-operated rats. However, the mean reaction time and distance of the Batroxobin-treated rats were shorter and they used normal strategies more often and earlier than those of ischemic rats. The number of HSP32 and HSP70 immune reactive cells of Batroxobin-treated rats was also less than that of the ischemic group. In conclusion, Batroxobin can improve spatial memory disorder of temporal ischemic rats; and the down-regulation of the expression of HSP32 and HSP70 is probably related to the attenuation of ischemic injury.

Chemoenzymatic synthesis of (+)-aspicilin from chlorobenzene

The enantiomerically pure cis-1,2-dihydrocatechol 2, which is obtained by microbial oxidation of chlorobenzene, has been converted, via intermediate 3, into the natural product (+)-aspicilin (1).

Identification of a novel kidney-specific gene downregulated in acute ischemic renal failure

To gain further insights into the molecular mechanisms involved in acute renal failure, we have isolated a new gene from rat and human, named KSP32 (kidney-specific protein with a molecular mass of 32 kDa). KSP32 encodes a novel gene that shows little homology to other mammalian proteins. It, however, shares extensive homology with several proteins found in the nematode Caenorhabditis elegans and plants. The expression of KSP32 mRNA is highly restricted to kidney. In situ hybidization analysis revealed that the expression of KSP32 mRNA was prominent in the boundary of kidney cortex and outer medulla, exhibiting a raylike formation extending from the medulla into the cortex. Finally, KSP32 mRNA was dramatically downregulated in rat following induction of acute ischemic renal failure. Rapid loss of KSP32 mRNA expression was observed beginning at approximately 5 h following renal injury and mRNA levels remained depressed for at least 96 h. Both KSP32 mRNA levels as well as renal function recovered 14 days after injury. Administration of an endothelin receptor antagonist (SB-209670), known to restore renal function, significantly increased KSP32 expression.

Anaerobic chlorophyll isocyclic ring formation in Rhodobacter capsulatus requires a cobalamin cofactor

The isocyclic ring of bacteriochlorophyll (BChl) is formed by the conversion of Mg-protoporphyrin monomethyl ester (MPE) to protochlorophyllide (PChlide). Similarities revealed by blast searches with the putative anaerobic MPE-cyclase BchE suggested to us that this protein also uses a cobalamin cofactor. We found that vitamin B(12) (B(12))-requiring mutants of the bluE and bluB genes of Rhodobacter capsulatus, grown without B(12), accumulated Mg-porphyrins. Laser desorption/ionization time-of-flight (LDI-TOF) MS and NMR spectroscopy identified them as MPE and its 3-vinyl-8-ethyl (mvMPE) derivative. An in vivo assay was devised for the cyclase converting MPE to PChlide. Cyclase activity in the B(12)-dependent mutants required B(12) but not protein synthesis. The following reaction mechanism is proposed for this MPE-cyclase reaction. Adenosylcobalamin forms the adenosyl radical, which leads to withdrawal of a hydrogen atom and formation of the benzylic-type 13(1)-radical of MPE. Withdrawal of an electron gives the 13(1)-cation of MPE. Hydroxyl ion attack on the cation gives 13(1)-hydroxy-MPE. Withdrawal of three hydrogen atoms leads successively to 13(1)-keto-MPE, its 13(2)-radical, and cyclization to PChlide.

The enhancement of the ability of mouse sperm to survive freezing and thawing by the use of high concentrations of glycerol and the presence of an Escherichia coli membrane preparation (Oxyrase) to lower the oxygen concentration

The cryobiological preservation of mouse spermatozoa has presented difficulties in the form of poor motilities or irreproducibility. We have hypothesized several underlying problems. One is that published studies have used concentrations of the cryoprotectant glycerol that are substantially lower (<0.3 M) than the approximately 1 M concentrations that are optimal for most mammalian cells. Another may arise from the known high susceptibility of mouse sperm to free radical damage. We have been able to obtain high motilities in 0.8 M glycerol provided that the exposure time is held to approximately 5 min to minimize toxicity and provided that the glycerol is added and removed stepwise to minimize osmotic shock. Since free radical damage in mouse sperm is proportional to the oxygen concentrations, we have determined the consequences of reducing the oxygen to <3% of atmospheric by maintaining the sperm in contact with an Escherichia coli membrane preparation, Oxyrase, from the moment of collection throughout the assessment of motility. Prior studies have shown that the procedure significantly reduces damage from centrifugation and osmotic shock. In the experiments reported here we obtained approximately 50% motility relative to untreated controls when suspensions containing 3.8% Oxyrase were exposed approximately 5 min to a solution of 0.8 M glycerol and 0.17 M (10%) raffinose in a supplemented PBS and then frozen at approximately 25 degrees C/min to -75 degrees C. In the absence of Oxyrase, the normalized motility dropped to 31%. The protection by Oxyrase was in part a consequence of minimizing centrifugation damage, but in part it reflected a reduction in freeze-thaw damage. Preliminary experiments indicate that the number of motile sperm after cryopreservation in Oxyrase is higher when the sperm are collected without swim-up than when they are collected by swim-up. This is in part due to the fact that more cells are collected in the absence of swim-up and in part due to a greater protective effect of Oxyrase on those cells. The minimum temperature in these initial experiments was limited to -75 degrees C to avoid the potential contribution of other injurious factors between -75 and -196 degrees C.

Heat shock proteins Hsp27 and Hsp32 localize to synaptic sites in the rat cerebellum following hyperthermia

Stressful stimuli activate the heat shock (stress) response in which a set of heat shock proteins (hsps) is induced, which play roles in cellular repair and protective mechanisms. Most studies in the mammalian nervous system have focused on Hsp70, however, the present investigation targets other members of the induced set, namely Hsp27 and Hsp32. In response to hyperthermia, these hsps are strongly induced in Bergmann glial cells in the rat brain and transported into their radial fibers, which project into the 'synaptic-enriched' molecular layer of the cerebellum. Using subcellular fractionation and immunoelectron microscopy, hyperthermia-induced Hsp27 and Hsp32 were detected in synaptic elements and in perisynaptic glial processes. These results suggest that stress-induced Hsp27 and Hsp32 may contribute to repair and protective mechanisms at the synapse.

Expression of stress proteins HSP 72 & HSP 32 in response to endotoxemia

Pretreatment with heat decreases mortality and acute lung injury in the rat septic shock model, presumably by the production of heat shock proteins (HSP). However, endotoxin, a severe cell stresser, has not been shown to induce HSP 70. We investigated the effects of severe endotoxemia on the expression of specific protective stress proteins, including HSP 72 (inducible HSP 70), HSP 32 (heme oxygenase-1), and HSP 90. Fifteen rats received intravenously either 3 mg/kg of endotoxin (E. coli O127:B8 lipopolysaccharide, LPS) (n=9) or saline (n=6). Two hr later the spleen was removed and splenocytes were separated into three groups and analyzed for specific HSP by Western blot. In Group 1, both endotoxin-treated and saline-treated splenocytes were incubated for 3 hr at 37 degrees C. In Group 2, the splenocytes were washed twice, then heat shocked for 30 min at 42 degrees C and subsequently incubated for 2.5 hr at 37 degrees C. In Group 3, splenocytes were washed twice, then incubated for 3.0 hr at 37 degrees C. HSP 90 & HSP 70c (constitutive) were present in all groups. Consistent with observations by others, HSP 72 was not induced in Group 1. HSP 72 was induced in both the saline-treated and endotoxin-treated splenocytes after heating (Group 2). However, in the absence of heat stress, HSP 72 was present in endotoxin-treated but not in saline-treated splenocytes after incubation (Group 3). Conversely, HSP 32, while present in Group 1 splenocytes, was not detected in the endotoxin-treated splenocytes of Group 2 and Group 3, but was present in the saline-treated cells. In conclusion, endotoxemic shock results in induction of HSP 72 and depletion of HSP 32, but only after the cells have been washed and further incubated.

PcpA, which is involved in the degradation of pentachlorophenol in Sphingomonas chlorophenolica ATCC39723, is a novel type of ring-cleavage dioxygenase

The pentachlorophenol (PCP) mineralizing bacterium Sphingomonas chlorophenolica ATCC39723 degrades PCP via 2,6-dichlorohydroquinone (2,6-DCHQ). The pathway converting PCP to 2,6-DCHQ has been established previously; however, the pathway beyond 2,6-DCHQ is not clear, although it has been suggested that a PcpA plays a role in 2, 6-DCHQ conversion. In this study, PcpA expressed in Escherichia coli was purified to homogeneity and shown to have novel ring-cleavage dioxygenase activity in conjunction with hydroquinone derivatives, and converting 2,6-DCHQ to 2-chloromaleylacetate.

In vitro studies on the initial reactions of anaerobic ethylbenzene mineralization

Anaerobic mineralization of ethylbenzene by the denitrifying bacterium Azoarcus sp. strain EB1 was recently shown to be initiated by dehydrogenation of ethylbenzene to 1-phenylethanol. 1-Phenylethanol is converted to benzoate (benzoyl coenzyme A) via acetophenone as transient intermediate. We developed in vitro assays to examine ethylbenzene dehydrogenase and 1-phenylethanol dehydrogenase activities in cell extracts of this strain. With p-benzoquinone as the electron acceptor, cell extracts of Azoarcus sp. strain EB1 catalyzed ethylbenzene oxidation at a specific rate of 10 nmol min(-1) [mg of protein](-1) and an apparent K(m) for ethylbenzene of approximately 60 microM. The membrane-associated ethylbenzene dehydrogenase activity was found to oxidize 4-fluoroethylbenzene and propylbenzene but was unable to transform 4-chloro-ethylbenzene, the ethyltoluenes, and styrene. Enzymatic ethylbenzene oxidation was stereospecific, with (S)-(-)-1-phenylethanol being the only enantiomer detected by chiral high-pressure liquid chromatography analysis. Moreover, cell extracts catalyzed the oxidation of (S)-(-)-1-phenylethanol but not of (R)-(+)-1-phenylethanol to acetophenone. When cell extracts were dialyzed, (S)-(-)-1-phenylethanol oxidation occurred only in the presence of NAD(+), suggesting that NAD(+) is the physiological electron acceptor of 1-phenylethanol dehydrogenase. Both ethylbenzene dehydrogenase and 1-phenylethanol dehydrogenase activities were present in Azoarcus sp. strain EB1 cells that were grown anaerobically on ethylbenzene, 1-phenylethanol, and acetophenone, but these activities were absent in benzoate-grown cells.

Attenuation of thrombin-induced brain edema by cerebral thrombin preconditioning

BACKGROUND AND PURPOSE

Edema formation after intracerebral hemorrhage has been linked to thrombin toxicity induced by the clot. However, thrombin at low concentrations actually protects neurons and astrocytes in culture from hypoglycemic and ischemic cell death. It is also known that a brief episode of brain ischemia increases neuronal tolerance to a subsequent severe ischemic episode. The objective of this study was to investigate whether pretreatment of the brain with low-dose thrombin induces tolerance to a subsequent large dose of thrombin injected into brain parenchyma.

METHODS

The rat brain was preconditioned with 1 U thrombin by direct infusion into the right caudate nucleus. After thrombin pretreatment, the effects of a large dose (5 U) of thrombin on brain edema formation were studied at different intervals. We examined whether heat-shock protein (HSP) 27, HSP32, and HSP70 were induced by Western blot analysis, immunocytochemistry, and immunofluorescent double staining.

RESULTS

Thrombin pretreatment significantly attenuated the brain edema that normally follows the infusion of a large dose of thrombin (79.2+/-0.4 versus 84.0+/-0.3; P<0.01). This effect was abolished by the thrombin inhibitor hirudin. Time course studies showed that the maximal effect of thrombin preconditioning (TPC) on brain edema formation was 7 days after pretreatment. This time course corresponded to marked upregulation of HSP27 in the ipsilateral brain. TPC also induced HSP32, but this effect occurred earlier than the effect on edema formation. TPC had no effect on HSP70. Immunocytochemistry and immunofluorescent double labeling showed that HSP27 and HSP32 were expressed in astrocytes after TPC.

CONCLUSIONS

OFF phenomenon of thrombin-induced tolerance of the brain to edema formation may be related to HSP27 induction.

Anti-oxidants prevent focal rat brain injury as assessed by induction of heat shock proteins (HSP70, HO-1/HSP32, HSP47) following subarachnoid injections of lysed blood

The initial aim of this study was to determine if the HSP70 (the main inducible heat shock protein), HO-1 (heme oxygenase-1, HSP32) and HSP47 (a collagen chaperone) stress proteins were induced in the same focal regions of rat brain following experimental subarachnoid hemorrhage (SAH). The next objective was to determine whether anti-oxidants prevented the stress gene expression in the focal regions. Lysed blood (150 microliter) was injected into the subarachnoid space of adult, female Sprague-Dawley rats via the cisterna magna. Animals were sacrificed 24 h later. Immunocytochemistry showed focal regions of stress gene induction in most animals (13/21), HSP70 and HO-1 proteins being expressed in neurons, microglia and astrocytes and HSP47 being expressed in microglia. Co-induction of the same three stress proteins was observed in focal areas in the striatum and cerebellum as well. In the 13 animals with focal regions of stress gene induction there were 8.1+/-1.8 foci in cortex, 5.5+/-0.9 foci in striatum, and 11.7+/-7.3 foci in cerebellum in the brain of each animal. The focal regions of stress gene induction varied in size from 200 micrometer to 7 mm in diameter. Systemic administration of the tirilazad-like anti-oxidants U101033E (n=8) and U74389G (n=7) completely blocked stress protein induction in focal brain regions normally produced by cisternal injections of lysed blood. There were fewer drug treated animals (0/15) with focal areas of stress gene induction compared to non-drug (13/21) treated animals following the cisternal lysed blood injections (p<0.01 using Fisher's probability test). This study shows that anti-oxidants prevent focal regions of injury as assessed by heat shock protein expression in a rat model of SAH.

Preferential injury of oligodendroblasts by a short hypoxic-ischemic insult

One-week-old rat pups were subjected to an acute 10 min severe hypoxic-ischemic insult. Over the next 24 h, during the reperfusion period, O4 immunocytochemistry demonstrated that oligodendroblasts underwent degenerative changes that were coincident with induction of heme oxygenase. We suggest that the increased vulnerability of oligodendroblasts to oxidative stress following an hypoxic-ischemic insult may contribute to the pathogenesis of periventricular leukomalacia.

Induction of apoptosis, p53 and heme oxygenase-1 by cytotoxic prostaglandin delta12-PGJ2 in transformed endothelial cells

Delta12-prostaglandin (PG)J2, which has been reported to have potent growth inhibitory activity in various tumor cells, induced apoptosis at 5 microg/ml culture medium in transformed mouse endothelial (F2) cells. Immunoblot analysis using anti-p53 or anti-WAF1 antibodies demonstrated that these two proteins had increased following delta12-PGJ2 treatment in F2 cells. Western blotting analysis using anti-heme oxygenase-1 (heat shock protein (HSP)32) antibody also revealed that delta12-PGJ2 induced HSP32 formation in F2 cells. HSP32 was also induced by heat shock treatment at 43 degrees C for 90 min. In contrast, HSP72 was not induced by heat shock or by delta12-PGJ2 treatment. In agreement with these findings, HSP32 immunofluorescence in the cytoplasm of F2 cells was intensified by delta12-PGJ2 treatment. More intense HSP32 immunoreactivity was similarly observed after heat shock treatment. These results suggest that delta12-PGJ2 caused the apoptotic cell death of F2 cells, which involved a certain process required for p53 or HSP32 induction.

Induction of HSP 32 gene in hypoxic cardiomyocytes is attenuated by treatment with N-acetyl-L-cysteine

Increased synthesis of stress proteins may enhance myocardial viability during periods of low oxygen delivery. Our purpose was to determine if the oxidative stress protein heme oxygenase-1 [heat stress protein 32 (HSP 32)] was induced in hypoxic cardiomyocytes and whether this induction might be mediated by a redox-sensitive mechanism. Primary rat neonatal cardiomyocytes, cultured to express a tissuelike phenotype, responded to 12 h of hypoxia (< 0.5% ambient oxygen) with an approximately fivefold (range 3- to 7.5-fold; P < 0.05) increase in HSP 32 mRNA and a threefold (P < 0.05) increase in HSP 32 protein content. Exposure to 80 microM H2O2 for 3 h increased HSP 32 mRNA content to a similar extent. Expression of heme oxygenase-2 mRNA was unaffected by H2O2 or hypoxic treatments. Inclusion of 20 mM N-acetyl-L-cysteine in the medium during hypoxia reduced the increase in HSP 32 mRNA and protein expression by 25.50% compared with hypoxia alone. The data suggest that induction of HSP 32 protein may lead to an improved antioxidant defense in cardiomyocytes during hypoxia and that a redox-sensitive pathway mediates at least a portion of the hypoxic induction of the HSP 32 gene.

Exceptionally stable salt bridges in cytochrome P450cam have functional roles

A long-standing puzzle in structure-function studies of cytochrome P450cam is how the substrate, camphor, reaches the buried active site. The crystal structure shows no channel from the surface to the active site large enough for substrate to pass through. Recent experiments indicate that access of the rather nonpolar substrate to the active site is controlled by electrostatic interactions and may involve rupture of the two salt links to Asp251 [Deprez, E., Gerber, N. C., Di Primo, C., Douzou, P., Sligar, S. G., & Hui Bon Hoa, G. (1994) Biochemistry 33, 14464-14468]. Consequently, we have computed the electrostatic strength of 53 ionic pairs, including 32 salt links, in cytochrome P450cam by numerical solution of the finite-difference linearized Poisson-Boltzmann equation. The calculated electrostatic free energies, delta Gtot, of the salt links range from -9 to +6 kcal/mol with approximately 60% of the salt links being energetically favorable and 40% being unfavorable with respect to mutation to their uncharged, nonpolar isosteres. Strikingly, of the four most stable salt links in the protein (delta Gtot < -6 kcal/mol), two involve the propionate groups of the heme and the other two involve Asp251. In the modeled D251N mutant, for which electrostatic effects on substrate binding are diminished, the latter two salt links lose their stability (delta Gtot > -2.4 kcal/mol). Thus it appears that cytochrome P450cam has evolved four unusually strong salt bridges, stabilized by surrounding charged and polar groups in the protein, to keep its heme cofactor in place and to regulate substrate binding.

EFFECTS OF BACTERIAL ENDOTOXINS ON METABOLISM. VII. ENZYME INDUCTION AND CORTISONE PROTECTION

Cortisone acetate administered to mice at the same time as either the LD(50) or 2 x LD(50) of endotoxin significantly protected against lethality. Delaying the injection of cortisone to 1, 2, or 4 hours after that of endotoxin resulted in loss of protection with the possible exception of a 1 hour delay with the LD(50) of endotoxin. Associated with this loss of protection was the failure of the hormone to induce liver tryptophan pyrrolase. Normal mice given only cortisone showed an increase in enzyme activity nearly three times that of control values when assays were carried out either 4 or 17 hours after the hormone was given. Endotoxin-poisoned mice showed normal levels of enzyme activity with concurrent injection of cortisone but depressed levels of enzyme when the cortisone injection was delayed for only 1 hour or more. Apparently, therefore, enzyme induction (or maintenance) is related to survival in endotoxin poisoning. In line with this hypothesis was the observation that inhibitors of enzyme (protein) synthesis were found to potentiate the lethal action of endotoxin and to prevent the protective effect of cortisone. The inhibitors employed were actinomycin D, ethionine, 2-thiouracil, and 8-azaguanine. Activity of liver tryptophan pyrrolase was lowered by endotoxin and elevated by cortisone. When the two were given concurrently, normal enzyme activity was maintained. Chloramphenicol, an active inhibitor of protein synthesis in microorganisms but with limited effect in mammals, was without observable influence in these respects. Mice 18 hours postinfection with Salmonella typhimurium, strain SR-11, given at a level that caused first deaths on the 3rd day, had a lower than normal activity of liver tryptophan pyrrolase and responded to cortisone induction with a smaller increase in enzyme level than that found in control mice. Each is characteristic of endotoxin poisoning. Animals 42 hours postinfection were free of these signs of endointoxication, an observation in agreement with earlier experiments where other measures of endotoxin were employed.