Coagulopathies and osteonecrosis

Intravascular coagulation of the intraosseous microcirculation (capillaries and venous sinusoids) progressing to generalized venous thrombosis, and less commonly retrograde arterial occlusion, now appears to be the cause of nontraumatic osteonecrosis. However, this coagulopathy is only an intermediary event, which is always activated by some underlying etiologic risk factor(s). Conditions capable of triggering intravascular coagulation include familial thrombophilia (resistance to activated protein C, decreased protein C, protein S, or antithrombin III), hyperlipemia and embolic lipid (alcoholism and hypercortisonism), hypersensitivity reactions (allograft organ rejection, immune complexes, and antiphospholipid antibodies), bacterial endotoxic (Shwartzman) reactions and various viral infections, proteolytic enzymes (pancreatitis), tissue factor release (inflammatory bowel disease, malignancies, neurotrauma, and pregnancy), and other prothrombotic and hypofibrinolytic conditions.

Oxidation of polychlorinated benzenes by genetically engineered CYP101 (cytochrome P450(cam))

Polychlorinated benzenes are recalcitrant environmental pollutants primarily because they are resistant to attack by dioxygenases commonly used by micro-organisms for the biodegradation of aromatic compounds. We have investigated the oxidation of polychlorinated benzenes by mutants of the haem mono-oxygenase CYP101 (cytochrome P450(cam)) from Pseudomonas putida with the aim of generating novel systems for their biodegradation. Wild-type CYP101 had low activity for the oxidation of dichlorobenzenes and trichlorobenzenes to the chlorophenols, but no products were detected for the heavily chlorinated benzenes. Increasing the active-site hydrophobicity with the Y96F mutation increased the activity up to 100-fold, and both pentachlorobenzene and hexachlorobenzene were oxidized slowly to pentachlorophenol. Decreasing the space available at the top of the active site with the F87W mutation to force the substrate to be bound closer to the haem resulted in a further 10-fold increase in activity with most substrates. Introducing the F98W mutation, also at the top of the active site, decreased the NADH-turnover rates but increased the coupling efficiencies, and > 90% coupling was observed for 1,3-dichlorobenzene and 1,3,5-trichlorobenzene with the F87W--Y96F--F98W mutant. The V247L mutation generally increased the NADH-turnover rates, and the F87W--Y96F--V247L mutant showed reasonably fast NADH turnover (229 min(-1)) with the highly insoluble pentachlorobenzene without the need for surfactants or organic cosolvents. As all chlorophenols are degraded by micro-organisms, novel biodegradation systems could be constructed in which CYP101 mutants convert the inert polychlorinated benzenes to the phenols, which are then readily degraded by natural pathways.

A refined 3-dimensional QSAR of cytochrome P450 2C9: computational predictions of drug interactions

A ligand-based model is reported that predicts the Ki values for cytochrome P450 2C9 (CYP2C9) inhibitors. This CoMFA model was used to predict the affinity of 14 structurally diverse compounds not in the training set and appears to be robust. The mean error of the predictions is 6 microM. The experimentally measured Ki values of the 14 compounds range from 0.1 to 48 microM. Leave-one-out cross-validated partial least-squares gives a q2 value of between 0.6 and 0.8 for the various models which indicates internal consistency. Random assignment of biological data to structure leads to negative q2 values. These models are useful in that they establish a pharmacophore for binding to CYP2C9 that can be tested with site-directed mutagenesis. These models can also be used to screen for potential drug interactions and to design compounds that will not bind to this enzyme with high affinity.

Group II introns designed to insert into therapeutically relevant DNA target sites in human cells

Mobile group II intron RNAs insert directly into DNA target sites and are then reverse-transcribed into genomic DNA by the associated intron-encoded protein. Target site recognition involves modifiable base-pairing interactions between the intron RNA and a >14-nucleotide region of the DNA target site, as well as fixed interactions between the protein and flanking regions. Here, we developed a highly efficient Escherichia coli genetic assay to determine detailed target site recognition rules for the Lactococcus lactis group II intron Ll.LtrB and to select introns that insert into desired target sites. Using human immunodeficiency virus-type 1 (HIV-1) proviral DNA and the human CCR5 gene as examples, we show that group II introns can be retargeted to insert efficiently into virtually any target DNA and that the retargeted introns retain activity in human cells. This work provides the practical basis for potential applications of targeted group II introns in genetic engineering, functional genomics, and gene therapy.

[Epidemiological risk factors for non-traumatic osteonecrosis]

Certain fractures and/or dislocations of the femoral head are known to cause arterial injury and result in post-traumatic osteonecrosis. However, the more complex etiology of non-traumatic osteonecrosis is multifactorial and includes chemotherapy, radiotherapy, thermal injuries, and especially coagulopathies, which are now commonly observed in these patients. Intravascular coagulation with fibrin thrombosis begins in the capillaries and sinusoids of the intraosseous microcirculation, and residual venous thrombosis is more likely to occur if there is coexistent hypofibrinolysis. Coagulopathies are intermediary events, which are always activated by some underlying etiologic risk factor(s). Conditions capable of triggering intravascular coagulation include familial thrombophilia (resistance to activated protein C, decreased protein C, protein S, or antithrombin III, and hyperhomocystinemia), hyperlipemia and embolic lipid (alcoholism and hypercortisonism), hypersensitivity reactions (allograft organ rejection, immune complexes, and antiphospholipid antibodies), bacterial endotoxic (Shwartzman) reactions and various viral infections, proteolytic enzymes (pancreatitis), tissue factor release (inflammatory bowel disease, malignancies, neurotrauma, and pregnancy), and other thrombophilic and hypofibrinolytic disorders. Currently known risk factors for non-traumatic osteonecrosis of the femoral head are described briefly in this review article.

Mechanism-based inactivation of cytochrome P450 3A4 by L-754,394

Mechanism-based inactivation of human liver P450 3A4 by L-754,394, a Merck compound synthesized as a potential HIV protease inhibitor, was investigated using recombinant P450 3A4. Enzyme inactivation was characterized by a small partition ratio (3.4 or 4.3 +/- 0.4), i.e., the total number of metabolic events undergone by the inhibitor divided by the number of enzyme inactivating events, lack of reversibility upon extensive dialysis, no decrease in the characteristic 450-nm species relative to control, and covalent modification of the apoprotein. The major and minor products formed during the inactivation of P450 3A4 were the monohydroxylated and the dihydrodiol metabolites of L-754,394, respectively. L-754,394 that had been adducted to P450 3A4 was hydrolyzed under the conditions used for SDS-PAGE, Ni(2+) affinity chromatography, and proteolytic digestion. In addition, the modification was not stable to the acidic conditions of HPLC separation and CNBr digestion. The labile nature of the peptide adduct and the nonstoichiometric binding of the inactivating species to P450 3A4 precluded the direct identification of a covalently modified amino acid residue or the peptide to which it was attached. However, Tricine SDS-PAGE in combination with MALDI-TOF-MS and homology modeling, allowed I257-M317 to be tentatively identified as an active site peptide, while prior knowledge of the stability of N-, O-, and S-linked conjugates of activated furans implicates Glu307 as the active site amino acid that is labeled by L-754, 394.

Structured long-range connections can provide a scaffold for orientation maps

In the visual cortex of the cat and ferret, it is established that maturation of orientation selectivity is shaped by experience-dependent plasticity. However, recent experiments indicate that orientation maps are remarkably stable and experience-independent. We present a model to account for these seemingly paradoxical results. In this model, a scaffold consisting of non-isotropic lateral connections is laid down in horizontal circuitry before visual experience. These lateral connections provide an experience-independent framework for the developing orientation maps by inducing a broad orientation tuning bias in the model neurons. Experience-dependent plasticity of the thalamocortical connections sharpens the tuning while the preferred orientation of the neurons remains unchanged. This model is verified by computer simulations in which the scaffolds are generated both artificially and inferred from experimental optical imaging data. The plasticity is modeled by the BCM synaptic plasticity rule, and the input environment consists of natural images. We use this model to provide a possible explanation of the recent observation in which two eyes without common visual experience develop similar orientation maps. Finally, we propose an experiment involving the disruption of lateral connections to distinguish this model from models proposed by others.

A life-cycle approach to ministry with the aging

Notes that the demographic predictions of dramatic increase in the number of elderly members of local congregations will change the focus and emphasis in pastoral ministry in the next millennium as the needs of the aging take precedence. Argues for a comprehensive, life-cycle approach to ministries with the aging that integrates theology and the behavioral sciences. Offers examples and practical methods for ministering more effectively to this important and growing population in the local church.

Outbreak of False Smut of Rice in Louisiana

False smut, caused by Ustilaginoidea virens (Cooke) Takah., has been occurring in Louisiana rice since at least 1906 (4). A color plate (no. 69) of the disease was published in the Compendium of Rice Diseases published by the American Phytopathological Society (3). The slide for this plate was taken by M. C. Rush in 1976 of rice grown at the Rice Research Station at Crowley, LA. Since that time, the disease has been sporadic and light in Louisiana. In 1997, however, incidence was high. False smut was present on many germ plasms at the Rice Research Station in Crowley and was observed on commercial cultivars in several growers' fields in southwestern Louisiana. Incidence ranged from 1 to 15% of tillers infected with at least two to three spore balls per infected panicle. The disease occurred on both long- and medium-grain cultivars. False smut of rice occurs in the field at the hard dough to mature stages of the crop. A few spikelets in a panicle transform into globose, yellowish green, velvety spore balls that are 2 to 5 cm in diameter and covered by a thin orange membrane. The membrane bursts open and releases powdery dark green spores. The chlamydospores formed in the spore balls are spherical to elliptical, warty, olivaceous, and 3 to 5 × 4 to 6 μm in dimension. Some of the spore balls develop one or more sclerotia, which are the overwintering structure, in the center. False smut has been considered a minor disease of rice that occurs sporadically in Louisiana. The recent discovery of ustilotoxin, a phytotoxin and mycotoxin, produced by this pathogen on diseased tissues suggests that the fungus may be of concern as a contaminant on rice products consumed by livestock and humans (1,2). This increases the need to monitor the incidence of this disease. References: (1) Koiso et al. Ustiloxin: A phytotoxin and a mycotoxin from false smut balls on rice panicles. Tetrahedron Lett. 33:4157, 1992. (2) Koiso et al. Ustiloxins, antimitotic cyclic peptides from false smut balls on rice panicles caused by Ustilaginoidea virens. J. Antibiot. 47:765, 1994. (3) F. N. Lee and P. S. Gunnel. 1992. Compendium of Rice Diseases. The American Phytopathological Society, St. Paul, MN. p. 28. (4) W. A. Orton. 1907. Plant diseases of 1906. Yearbook U.S. Department of Agriculture. U.S. Government Printing Office, Washington, DC, pp. 499-508.

Choline availability to the developing rat fetus alters adult hippocampal long-term potentiation

Supplementation with choline during pregnancy in rats causes a long-lasting improvement of visuospatial memory of the offspring. To determine if the behavioral effects of choline are related to physiological changes in hippocampus, the effect of perinatal choline supplementation or deficiency on long-term potentiation (LTP) was examined in hippocampal slices of 6-8 and 12-14 month old rats born to dams consuming a control, choline-supplemented, or a choline-free diet during pregnancy. Stimulating and recording electrodes were placed in stratum radiatum of area CA1 to record extracellular population excitatory postsynaptic potentials (pEPSPs). To induce LTP, a theta-like stimulus train was generated. The amplitude of the stimulus pulses was set at either 10% or 50% of the stimulus intensity which had induced the maximal pEPSP slope on the input/output curve. We found that at both ages, a significantly smaller percentage of slices from perinatally choline-deficient rats displayed LTP after 10% stimulus intensity (compared with control and choline-supplemented rats), and a significantly larger percentage of slices from choline-supplemented rats displayed LTP at 50% stimulus intensity (compared with control and choline-deficient rats). Results reveal that alterations in the availability of dietary choline during discrete periods of development lead to changes in hippocampal electrophysiology that last well into adulthood. These changes in LTP threshold may underlie the observed enhancement of visuospatial memory seen after prenatal choline supplementation and point to the importance of choline intake during pregnancy for development of brain and memory function.

Structural forms of phenprocoumon and warfarin that are metabolized at the active site of CYP2C9

Possible reasons for the observed differences in metabolic behavior and drug interaction liability between the structurally similar oral anticoagulants warfarin and phenprocoumon were explored. Incubating (S)-phenprocoumon with human liver microsomes and cDNA-expressed CYP2C9 and determining its metabolism both in the absence and presence of the CYP2C9 inhibitor, sulfaphenazole, confirmed that phenprocoumon is a substrate for CYP2C9. Comparing the metabolic behavior of (S)- and (R)-warfarin, (S)- and (R)-phenprocoumon, and fixed structural mimics of the various tautomeric forms [(S)- and (R)-4-methoxyphenprocoumon, (S)- and (R)-2-methoxyphenprocoumon, (S)- and (R)-4-methoxywarfarin, (S)- and (R)-2-methoxywarfarin, and 9(S)- and 9(R)-cyclocoumarol] available to these two drugs with expressed CYP2C9 provides compelling evidence indicating that the ring closed form of (S)-warfarin and the ring opened anionic form of (S)-phenprocoumon are the major and specific structural forms of the two drugs that interact with the active site of CYP2C9. The conclusion that (S)-warfarin and (S)-phenprocoumon interact with CYP2C9 in very different structural states provides a clear basis for the significant differences observed in their metabolic profiles. Moreover, in accord with a previously established CoMFA model these results are consistent with the hypothesis that the active site of CYP2C9 possesses at least two major substrate binding sites, a pi-stacking site for aromatic rings and an ionic binding site for organic anions. An additional electrostatic binding site also appears to contribute to the orientation of coumarin analogs in the CYP2C9 active site by interacting with the C2-carbonyl group of the coumarin nucleus.

Normative data for the Novaco Anger Scale from a non-clinical sample and implications for clinical use

OBJECTIVES

To provide non-clinical normative data for the Novaco Anger Scale. To identify the ability of the scale to discriminate between clinical and non-clinical populations.

DESIGN

Postal survey of individuals from a non-clinical sample.

METHOD

A non-clinical sample of 212 NHS employees was sent a questionnaire pack, including the Novaco Anger Scale. A clinical sample of 58 outpatient anger-management referrals was identified from a retrospective case-note analysis.

RESULTS

Descriptive data are presented for both samples. t-score conversions are provided, based on the non-clinical data. Results from a discriminant function analysis demonstrated that the Novaco Anger Scale classified participants as clinical or non-clinical with 94% accuracy.

CONCLUSION

From this study it appears that the Novaco Anger Scale is able to discriminate between clinical and non-clinical populations. These data offer further support to the validity of the Novaco Anger Scale and its use in clinical assessment.

The domain structure and retrotransposition mechanism of R2 elements are conserved throughout arthropods

R2 elements are non-LTR retrotransposons that insert in the 28S rRNA genes of arthropods. Partial sequence data from many species have previously suggested that these elements have been vertically inherited since the origin of this phylum. Here, we compare the complete sequences of nine R2 elements selected to represent the diversity of arthropods. All of the elements exhibited a uniform structure. Identification of their conserved sequence features, combined with our biochemical studies, allows us to make the following inferences concerning the retrotransposition mechanism of R2. While all R2 elements insert into the identical sequence of the 28S gene, it is only the location of the initial nick in the target DNA that is rigidly conserved across arthropods. Variation at the R2 5' junctions suggests that cleavage of the second strand of the target site is not conserved within or between species. The extreme 5' and 3' ends of the elements themselves are also poorly conserved, consistent with a target primed reverse transcription mechanism for attachment of the 3' end and a template switch model for the attachment of the 5' end. Comparison of the approximately 1,000-aa R2 ORF reveals that it can be divided into three domains. The central 450-aa domain can be folded by homology modeling into a tertiary structure resembling the fingers, palm, and thumb subdomains of retroviral reverse transcriptases. The carboxyl terminal end of the R2 protein appears to be the endonuclease domain, while the amino-terminal end contains zinc finger and c-myb-like DNA-binding motifs.

Flavone antagonists bind competitively with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) to the aryl hydrocarbon receptor but inhibit nuclear uptake and transformation

Previous analyses suggested that potent aryl hydrocarbon receptor (AhR) antagonists were planar, with a lateral electron-rich center. To further define structural requirements and mechanism for antagonism, ten additional flavone derivatives were synthesized. Based on their ability to 1) compete with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) for binding to the AhR; 2) inhibit TCDD-elicited binding of AhR to dioxin-responsive elements (DRE) in vitro; and 3) inhibit TCDD-induced transcription of DRE-dependent luciferase in stably transfected hepatoma cells, the most potent flavones contained a 3'-methoxy group and a 4'-substituent having one or more terminal atoms of high electron density (-N3, -NO2, or -NCS). Furthermore, these had low agonist activity as assessed by their inability to elicit AhR. DRE binding or to induce luciferase. Compounds containing bulkier 3' or 4'-substituents, or a 3'-OH group were less potent antagonists, and some were partial agonists. In rat liver cytosol, 3'-methoxy-4'-azido- and 3'-methoxy-4'-nitroflavones bound competitively (with TCDD) to the AhR, indicating that they bind to the TCDD-binding site. When hepatoma cells were exposed to these flavones, AhR complexes were primarily immunoprecipitable from the cytosol and contained 90 kDa heat shock protein. In contrast, AhR in TCDD-treated cells was primarily immunoprecipitated from nuclear extracts and was associated with Arnt but not 90 kDa heat shock protein. Immunocytofluorescence analysis in intact cells further indicated that the potent antagonist inhibited nuclear uptake of AhR and blocked TCDD-dependent down-regulation of AhR. Together, these data indicate that the most potent antagonists bind the AhR with high affinity but cannot initiate receptor transformation and nuclear localization.

Enzymatic determinants of the substrate specificity of CYP2C9: role of B'-C loop residues in providing the pi-stacking anchor site for warfarin binding

Previous modeling efforts have suggested that coumarin ligand binding to CYP2C9 is dictated by electrostatic and pi-stacking interactions with complementary amino acids of the protein. In this study, analysis of a combined CoMFA-homology model for the enzyme identified F110 and F114 as potential hydrophobic, aromatic active-site residues which could pi-stack with the nonmetabolized C-9 phenyl ring of the warfarin enantiomers. To test this hypothesis, we introduced mutations at key residues located in the putative loop region between the B' and C helices of CYP2C9. The F110L, F110Y, V113L, and F114L mutants, but not the F114Y mutant, expressed readily, and the purified proteins were each active in the metabolism of lauric acid. The V113L mutant metabolized neither (R)- nor (S)-warfarin, and the F114L mutant alone displayed altered metabolite profiles for the warfarin enantiomers. Therefore, the effect of the F110L and F114L mutants on the interaction of CYP2C9 with several of its substrates as well as the potent inhibitor sulfaphenazole was chosen for examination in further detail. For each substrate examined, the F110L mutant exhibited modest changes in its kinetic parameters and product profiles. However, the F114L mutant altered the metabolite ratios for the warfarin enantiomers such that significant metabolism occurred for the first time on the putative C-9 phenyl anchor, at the 4'-position of (R)- and (S)-warfarin. In addition, the Vmax for (S)-warfarin 7-hydroxylation decreased 4-fold and the Km was increased 13-fold by the F114L mutation, whereas kinetic parameters for lauric acid metabolism, a substrate which cannot interact with the enzyme by a pi-stacking mechanism, were not markedly affected by this mutation. Finally, the F114L mutant effected a greater than 100-fold increase in the Ki for inhibition of CYP2C9 activity by sulfaphenazole. These data support a role for B'-C helix loop residues F114 and V113 in the hydrophobic binding of warfarin to CYP2C9, and are consistent with pi-stacking to F114 for certain aromatic ligands.

Regulation of skeletal muscle UCP-2 and UCP-3 gene expression by exercise and denervation

The factors that regulate gene expression of uncoupling proteins 2 and 3 (UCP-2 and UCP-3) in skeletal muscle are poorly understood, but both genes are clearly responsive to the metabolic state of the organism. Therefore, we tested the hypothesis that denervation and acute and/or chronic exercise (factors that profoundly affect metabolism) would alter UCP-2 and UCP-3 gene expression. For the denervation studies, the sciatic nerve of rat and mouse hindlimb was sectioned in one leg while the contralateral limb served as control. Northern blot analysis revealed that denervation was associated with a 331% increase (P < 0.001) in UCP-3 mRNA and a 200% increase (P < 0. 01) in UCP-2 mRNA levels in rat mixed gastrocnemius (MG) muscle. In contrast, denervation caused a 53% decrease (P < 0.001) in UCP-3 and a 63% increase (P < 0.01) in UCP-2 mRNA levels in mouse MG. After acute exercise (2-h treadmill running), rat UCP-3 mRNA levels were elevated (vs. sedentary control) 252% (P < 0.0001) in white gastrocnemius and 63% (P < 0.05) in red gastrocnemius muscles, whereas UCP-2 levels were unaffected. To a lesser extent, elevations in UCP-3 mRNA (22%; P < 0.01) and UCP-2 mRNA (55%; P < 0.01) levels were observed after acute exercise in the mouse MG. There were no changes in either UCP-2 or UCP-3 mRNA levels after chronic exercise (9 wk of wheel running). These results indicate that acute exercise and denervation regulate gene expression of skeletal muscle UCPs.

Borderline necrosis of the femoral head

To determine whether the histologic lesions classified by the system of Arlet et al as Type 2 (granular necrosis of fatty marrow) and Type 3 (complete medullary and trabecular necrosis) always progress to Type 4 (complete necrosis with marginal medullary fibrosis and appositional new bone formation), 10 femoral heads (nine patients) were monitored for 4 years using serial magnetic resonance images. These femoral heads had been diagnosed histologically as having either Type 2 (seven hips) or Type 3 (three hips) necrosis on initial core biopsies. On the initial magnetic resonance image, none of the femoral heads showed any focal lesions indicative of osteonecrosis. In all instances, superselective angiography showed interruption of the superior retinacular artery, and the bone marrow pressure was elevated. During a followup period of 48 to 54 months, no patient had a reactive low signal intensity band develop on T1 weightings, as evidence of a reparative process around the necrotic portion of the lesion, or any other findings of osteonecrosis on magnetic resonance images. These findings suggest that some Type 2 and 3 lesions of Arlet et al may not develop an obvious reactive interface of reparative revascularization and thus may not progress to definite and classic Type 4 osteonecrosis. This study supports the hypothesis that there is an ischemic threshold between reversible intraosseous hypoxia (bone marrow edema syndrome) and irreversible intraosseous anoxia (classic bone infarction or osteonecrosis) and suggests that borderline necrosis occurs in the transition zone of this ischemic threshold and is nonprogressive.

Structure-function of cytochromes P450 and flavin-containing monooxygenases: implications for drug metabolism

This article is a report on a symposium held at Experimental Biology '98 in San Francisco, California. Recent developments in site-directed mutagenesis, computer-modeling, and mechanistic analysis of cytochromes P450 and flavin-containing monooxygenases are described. A unifying theme is the elaboration of general approaches for understanding and predicting the function of individual forms of these enzymes. A related goal is the production of soluble forms of mammalian cytochromes P450 for X-ray crystallography.

First Report of the Occurrence of White Leaf Streak in Louisiana Rice

White leaf streak, caused by Mycovellosiella oryzae (Deighton and Shaw) Deighton (syn. Ramularia oryzae), was found in Louisiana rice. The symptoms closely resemble those of narrow brown leaf spot caused by Cercospora janseana (Racib.) O. Const. (syn. C. oryzae (Miyake)), and it is difficult to distinguish between these two diseases. Initially both produce similar elongated light brown lesions, but later the lesions of white leaf streak become wider with a whitish center and are surrounded by a narrow light brown margin (2,3). The disease was first observed at the Rice Research Station, Crowley, LA, in 1996 on older leaves of the cultivar Lemont at maturity. Leaves containing the unusual lesion types were placed in a moist chamber and incubated at 28°C for 5 days. Abundant conidia were produced and the fungus was isolated on acidified potato dextrose agar (APDA) by single spore isolation and by plating infected tissues after surface sterilization in 40% Clorox for 10 to 15 min. The colonies grew slowly on APDA and were dark gray in color. The conidia formed in branched chains or singly. They were hyaline, cylindrical with tapering ends and a thick hilum; 0 to 3 septate, and 15 to 35 m long (1,3). Pathogenicity tests were conducted in the greenhouse on the Lemont and Cypress rice cultivars by spraying a conidial suspension (10^3-4 conidia per ml) onto leaf blades at boot stage. Conidia were produced by growing the fungus on PDA for 10 to 14 days. Inoculated plants were placed inside a humid chamber in a greenhouse and maintained for 4 to 5 weeks. Many elongated lesions similar to those observed in the field were produced 3 to 4 weeks after inoculation. Reisolation from these lesions yielded M. oryzae. With the same methods, 45 cultivars and lines were inoculated to determine their reactions to this disease. Most of the cultivars grown in the southern United States were moderately susceptible or susceptible to white leaf streak. Foreign cultivars tested, including BR-7, BR-11, Cica-4, Cica-6, Cica-7. Cica-8, Cica-9, Oryzica llanos, Rax clear, Teqing, and Tetep, were resistant. In 1997, the disease was found prevalent on many cultivars grown at the Rice Research Station, Crowley, LA. As symptoms of both white leaf streak and narrow brown leaf spot were sometimes observed on the same leaf; it is possible that the disease has been present, but not identified as a separate disease because of the similarity of the symptoms of the two diseases. A thorough survey is necessary to determine the extent of its occurrence and further studies are necessary to determine its yield loss potential. At present it appears to be a minor problem for Louisiana rice. White leaf streak has previously been recorded from Papua New Guinea on cultivated Oryza sativa, and from the Solomon Islands, Sabah, Nizeria, and Sierra Leone on cultivated O. glabberima Steudel and on wild perennial rice O. berthii A. Chev. (2). This is the first report of white leaf streak on cultivated rice in the United States. References: (1) F. C. Deighton. Mycol. Pap., CMI 144:1,1979. (2) F. C. Deighton and D. Shaw. Trans. Br. Mycol. Soc. 43: 515, 1960. (3) B. C. Sutton and A. K. M. Shahjahan. Nova Hedwigia 25:197, 1981.

An investigation of possible effects of high-frequency ultrasound on cellular integrity of cultured fibroblasts

Several investigators have demonstrated the feasibility of imaging at the cellular level using acoustical microscopy. It has also been proposed that acoustical microscopy technology might be adopted for in vivo applications. Before such applications are implemented, it is important to demonstrate that any major deleterious effects are highly unlikely. To this end, we have repeatedly scanned NIH/3T3 mouse fibroblasts in culture using an Olympus UH3 acoustical microscope operating at 600 MHz. No adverse effects were observed even after exposures for 1 h. Spatial peak temporal averaged intensities were estimated to be below 300 mW/cm2.

Design of a novel P450: a functional bacterial-human cytochrome P450 chimera

We report the construction of a functional chimera from approximately 50% bacterial (cytosolic) cytochrome P450cam and 50% mammalian (membrane-bound) cytochrome P450 2C9. The chimeric protein shows a reduced CO-difference spectrum absorption at 446 nm, and circular dichroism spectra indicate that the protein is globular. The protein is soluble and catalyzes the oxidation of 4-chlorotoluene using molecular oxygen and reducing equivalents from bacterial putidaredoxin and putidaredoxin reductase. This chimera provides a novel method for addressing structure-function issues and may prove useful in the design of oxidants for benign and stereospecific synthesis, as well as catalysts for bioremediation of polluted areas. Furthermore, these results provide the first evidence that bacterial P450 enzymes and mammalian P450 enzymes are likely to share a common tertiary structure.

Evaluation of cytochrome P450 mechanism and kinetics using kinetic deuterium isotope effects

In this paper two hypotheses are tested: (i) the active oxygen species is similar in energetics for all cytochrome P450 (CYP) enzymes and (ii) linear free-energy relationships can be used to evaluate the mechanism of the reaction of these enzymes. A series of intramolecular isotope effects were determined and compared for CYPs 1A2, 2B1, 2C9, 2E1, and P450cam. The results indicate that the isotope effects are very similar for each of these isoforms of P450 and that the first hypothesis is likely to be true. Attempts to establish a linear free-energy relationship were only moderately successful: log Vmax = 0.11sigma+p + 1.73; r2 = 0.588. It was determined, through the use of intermolecular isotope effects, that the rates of hydrogen atom abstraction are masked. Thus, the second hypothesis is found to be false. This is likely to be a general result for CYP reactions, and linear free-energy relationships can only be used to determine the mechanism under very special circumstances. In all cases, the rate-limiting step should be evaluated with isotope effect experiments before any mechanistic conclusions can be drawn. If the intermolecular isotope effects are found to be masked, no mechanistic conclusion can be drawn from the linear free-energy relationship study.

Focused ultrasound modifications of neural circuit activity in a mammalian brain

The application of focused, pulsed ultrasound was studied as a method of modifying the activity of a local neural circuit of the mammalian brain. An in vitro hippocampal preparation was used to facilitate delivery, dosimetry and assessment of mechanisms of ultrasound effects. Extracellular evoked potentials were recorded from cell and dendritic layers of the rat hippocampal dentate gyrus. Focused pulses of ultrasound with center frequency of 500 kHz and repetition rate of 200 kHz were studied and found both to enhance and to depress electrically evoked field potentials. The fiber volley and cell population potentials were depressed, whereas the dendritic potential was enhanced. Results suggest a simultaneous mechanical and thermal mechanism of ultrasound in modifying evoked field potentials of dentate local circuits.