gyrA mutations in ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus from Indiana, Minnesota, and Tennessee

Mutational changes occurring at amino acid codons 84 and 85 located in the gyrA gene of methicillin-resistant Staphylococcus aureus (MRSA) were studied using radiolabeled oligonucleotide probes to examine the incidence of these ciprofloxacin resistance determinants in 30 MRSA isolates from Indiana, Minnesota, and Tennessee. Four separate oligonucleotide probes, one each corresponding to the wild-type sequence, a mutation at codon 84 (nucleotide 251), a mutation at codon 85 (nucleotide 253), and mutations at both, were used to examine the total genomic DNA from each of the 30 isolates, which had been restricted, electrophoresed, and Southern blotted. The probes indicated that 15 of the 28 ciprofloxacin-resistant isolates gave results consistent with a single mutation at codon 84. Four of the 28 ciprofloxacin-resistant strains had results consistent with a mutation at codon 84 and possibly at codon 85. The two ciprofloxacin-sensitive isolates from Tennessee showed homology with the wild-type probe sequence. Five isolates (4, Minnesota; 1, Tennessee) had no homology with any probe. By oligonucleotide probes, ciprofloxacin-resistant MRSA from diverse geographic regions contained similar gyrA mutations at codons 84 or 85 in 19 of 28 ciprofloxacin-resistant isolates.

Ciprofloxacin resistance in coagulase-positive and -negative staphylococci: role of mutations at serine 84 in the DNA gyrase A protein of Staphylococcus aureus and Staphylococcus epidermidis

gyrA mutations in quinolone-resistant pathogenic isolates of Staphylococcus spp. have been detected by the direct HinfI digestion of polymerase chain reaction products. Homology among gyrA genes allowed rapid examination of both coagulase-positive and -negative isolates. DNA sequence analysis revealed that ciprofloxacin resistance in Staphylococcus epidermidis is associated with a novel Ser-84----Phe mutation in the DNA gyrase A protein, analogous to Ser-84----Leu changes observed in Staphylococcus aureus.

4-Quinolone resistance mutations in the DNA gyrase of Escherichia coli clinical isolates identified by using the polymerase chain reaction

Seven nalidixic acid-resistant clinical isolates of Escherichia coli were shown to carry resistance mutations in their gyrase A proteins. Six had serine-83 to leucine or tryptophan changes; the seventh had an aspartate-87 to valine substitution. The frequent occurrence of a mutation at serine-83 implies a key role for this residue in quinolone action.

DNA gyrase gyrA mutations in ciprofloxacin-resistant strains of Staphylococcus aureus: close similarity with quinolone resistance mutations in Escherichia coli

The gyrA genes isolated from three ciprofloxacin-resistant clinical isolates of Staphylococcus aureus carried codon 84 (serine----leucine) and/or codon 85 (serine----proline) mutations that were absent in pretreatment susceptible strains. These substitutions occur in a region of the gyrase A protein wherein directly analogous mutations of serine 83----leucine and alanine 84----proline in Escherichia coli confer quinolone resistance. Thus, DNA gyrase A subunit mutations are implicated in resistance to ciprofloxacin in S. aureus.

Characteristics of telephone applicants to a residential rehabilitation program for homeless veterans

This study gathered descriptive data on 163 individuals who applied by telephone to a residential rehabilitation program for homeless veterans and compared these data with general veteran and homeless populations. Ss were a young (M = 40.82 years) and educated (M = 13.34 years of schooling) subgroup of homeless men (98.16%) with histories of relatively high, stable functioning (e.g., previous successful employment) and high rates of medical (47.47%), substance abuse (67.1%), psychiatric (41.93%; primarily nonpsychotic), and legal (71.15%) problems. These characteristics appear to be different from those of other subgroups of homeless (e.g., homeless chronically mentally ill, skid-row alcoholics), and they provide a basis for beginning to develop distinct remedial strategies that are specific to this subpopulation. The advantages of studying subgroups of homeless and the utility of the telephone interview data collection methodology are discussed.

Stroop Color-Word Test performance in patients with Alzheimer's disease

Patients with Alzheimer's disease (AD) (n = 36) and normal older adults (n = 36) were individually administered the Stroop Color-Word Test. Eight of 36 (22%) AD patients exhibited confusion between the colors blue and green, while no control subject had difficulty distinguishing among the colors. In a second experiment, a subset of the original sample (15 AD patients and 8 control subjects) was retested using the Stroop. Only 2 AD patients showed color confusion on both test occasions, while 7 AD patients exhibited color confusion on one occasion. No control subject exhibited confusion between colors the second time. These results indicate that color confusion in AD patients is inconsistent. Due to the high incidence of color confusion in AD patients, the Stroop should be used with caution in patient populations.

Identification of a factor IX point mutation using SSCP analysis and direct sequencing

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Structure and partial amino acid sequence of calf thymus DNA topoisomerase II: comparison with other type II enzymes

The partial amino acid sequence of p140 calf thymus DNA topoisomerase II was determined by analysis of cyanogen bromide peptides. Five peptides were aligned and shared extensive homology with sequences derived from cDNA clones for the human topoisomerase II isoenzyme forms. Less homology was seen with the Drosophila, yeast and bacterial type II enzymes. Calf and human enzymes shared epitopes allowing isolation of a cDNA clone to human topoisomerase II isoenzyme alpha. Our results indicate that calf thymus p140 topoisomerase II is an active N-terminal proteolytic fragment of the native p180 enzyme and demonstrate that mammalian type II enzymes exhibit close sequence similarity.

Isolation and characterization of a human cDNA clone encoding a novel DNA topoisomerase II homologue from HeLa cells

We have isolated and sequenced 3 human DNA topoisomerase II (topo II) partial cDNA clones from a HeLa carcinoma cell cDNA library. Two clones were identical to an internal fragment of HeLa topo II cDNA. The third clone, CAA5, had a different and novel sequence which shared significant nucleotide (62%) and predicted peptide (70%) homologies with a region of the HeLa topo II cDNA. Our results suggest that HeLa cells express at least two homologous forms of DNA topoisomerase II. The new HeLa topo II homologue is discussed in relation to topo II isoenzymes recently described in a Burkitt lymphoma and other cell lines.

DNA cloning and organization of the Staphylococcus aureus gyrA and gyrB genes: close homology among gyrase proteins and implications for 4-quinolone action and resistance

Staphylococcus aureus gyrA and gyrB genes, which encode the DNA gyrase A and B proteins, have been isolated and found to map contiguously. DNA sequence analysis revealed close homology between the S. aureus gyrase subunits and their counterparts in Bacillus subtilis and Escherichia coli, including several conserved amino acid residues whose substitution in E. coli confers resistance to 4-quinolones. These results are discussed in regard to quinolone resistance mechanisms in S. aureus.

DNA binding and intercalation by novel porphyrins: role of charge and substituents probed by DNase I footprinting and topoisomerase I unwinding

Porphyrins carrying four charged sidechains, e.g., meso-tetrakis[4-N-methylpyridiniumyl]- and meso-tetrakis[4-N-(2-hydroxyethyl)pyridiniumyl]-porphyrin, bound and intercalated similarly into DNA as measured by helix stabilization and DNA unwinding studies in the presence of DNA topoisomerase I. Despite their different bulky sidechains, these complexes gave essentially identical DNase I footprinting patterns. In contrast, tetrasubstituted porphyrins carrying three phenyl rings and a single positively charged pyridiniumyl sidechain did not intercalate and exhibited little affinity for DNA. Thus, the presence of charged sidechains on the porphyrin rather than their identity appears to be critical for efficient DNA intercalation. The results are discussed in regard to current models for the porphyrin-DNA intercalation complex.

Development and properties of an etoposide-resistant human leukaemic CCRF-CEM cell line

Etoposide (VP-16) and several other unrelated anti-tumour agents appear to act by inhibiting the enzyme DNA topoisomerase II. We report here the development and characterization of an etoposide-resistant human leukaemic CCRF-CEM cell line, CEM/VP-1. The cell line was 15-fold more resistant to etoposide than the parental CEM cells and exhibited cross-resistance to other topoisomerase II inhibitors including teniposide, m-AMSA, and doxorubicin. CEM/VP-1 cells exhibited only a low level cross-resistance to the Vinca alkaloids, vinblastine and vincristine, known inhibitors of mitotic spindle formation. As a first step in defining the mechanism of resistance to etoposide, we compared the levels of topoisomerase II activity and its drug sensitivity in nuclear extracts from the resistant and sensitive CEM cells. As determined by a kinetoplast DNA decatenation assay, the level of DNA topoisomerase II activity in CEM/VP-1 nuclear extracts was approximately 2-fold lower than that in CEM cells, and the activity appeared to be resistant to inhibition by etoposide. Furthermore, the DNA topoisomerase II activity in CEM/VP-1 nuclear extracts did not promote the etoposide-dependent cleavage of pBR322 DNA observed with extract from sensitive cells. These results suggest that etoposide resistance in the CEM/VP-1 cell line may at least in part be due to an altered topoisomerase II, or associated factor, resulting in a reduced ability to induce DNA cleavage in the presence of drug.

Characteristics of telephone applicants to a residential rehabilitation program for homeless veterans

This study gathered descriptive data on 163 individuals who applied by telephone to a residential rehabilitation program for homeless veterans and compared these data with general veteran and homeless populations. Ss were a young (M = 40.82 years) and educated (M = 13.34 years of schooling) subgroup of homeless men (98.16%) with histories of relatively high, stable functioning (e.g., previous successful employment) and high rates of medical (47.47%), substance abuse (67.1%), psychiatric (41.93%; primarily nonpsychotic), and legal (71.15%) problems. These characteristics appear to be different from those of other subgroups of homeless (e.g., homeless chronically mentally ill, skid-row alcoholics), and they provide a basis for beginning to develop distinct remedial strategies that are specific to this subpopulation. The advantages of studying subgroups of homeless and the utility of the telephone interview data collection methodology are discussed.

Ciprofloxacin and the fluoroquinolones. New concepts on the mechanism of action and resistance

Ciprofloxacin, a new fluoroquinolone, is a potent, broad-spectrum antibacterial agent. It rapidly blocks bacterial deoxyribonucleic acid (DNA) replication by inhibiting DNA gyrase, an essential prokaryotic enzyme that catalyzes chromosomal DNA supercoiling. Molecular genetic approaches have been used to study the interaction of 4-quinolones with DNA gyrase from quinolone-sensitive strains and from uropathogenic quinolone-resistant clinical isolates of Escherichia coli. An important mutational locus in the gyrase A gene that confers resistance to ciprofloxacin and other quinolones has been identified, and a new, rapid method to examine clinical isolates for the presence of mutations at this position has been devised. A quinolone resistant gyrA gene has been previously cloned and sequenced from an E. coli clinical isolate. Genetic analysis indicated that resistance resulted from a Ser-83----Trp change in the 875 residue gyrase A protein: two other changes observed in the protein, Asp-678----Glu and Ala-828----Ser, were neutral. GyrA genes carrying these mutations have now been expressed, corresponding mutant gyrase A proteins purified, and their quinolone resistance properties tested by complementing with gyrase B protein and studying the resulting gyrase activity in an adenosine triphosphate-dependent DNA supercoiling assay. The in vitro DNA supercoiling activity of the A (Ser-83----Trp) mutant subunit complemented with wild-type gyrase B subunit was highly resistant to ciprofloxacin and other 4-quinolones. In contrast, A subunit carrying codon 678 and 828 changes reconstituted a quinolone-sensitive gyrase activity. Thus, quinolone-resistant gyrase A proteins may be readily obtained for study by using high-copy gyrA plasmids. In addition, other quinolone-resistant strains of E. coli have been examined for the presence of mutations at gyrase A codons 82 and 83 using a new analytical method based on a restriction fragment length polymorphism (RFLP). This analysis revealed that seven of eight resistant clinical isolates of E. coli examined carried gyrA mutations at codon 82 or 83, whereas five sensitive strains appeared to possess wild-type sequence. Thus, mutations at codon 83 (and possibly 82) in the gyrA gene frequently confer resistance to 4-quinolones, including ciprofloxacin. The RFLP method described should prove useful in examining strains for such mutations. These results are discussed with regard to the mode of interaction of the 4-quinolones with gyrase.

Regulation of DNA supercoiling in Escherichia coli: genetic basis of a compensatory mutation in DNA gyrase

Bacterial DNA supercoiling is controlled by balancing the supercoiling activity of DNA gyrase and the relaxing activity of DNA topoisomerase I. We have characterized the gyrB gene from a top A deletion mutant of Escherichia coli (DM800) that has a compensatory mutation in gyrB, lowering the activity of gyrase 10-fold, and thereby redressing the intracellular level of supercoiling. The mutant gene differs from the wild type in carrying three rather than two direct tandem repeats of a 6 bp sequence encoding Ala-Arg. We suggest this novel mutation affects domain spacing and was generated by an unequal crossing over event, possibly involving gyrase.

Cloning and characterization of a DNA gyrase A gene from Escherichia coli that confers clinical resistance to 4-quinolones

Nalidixic acid, enoxacin, and other antibacterial 4-quinolones inhibit DNA gyrase activity by interrupting DNA breakage and reunion by A subunits of the A2B2 gyrase complex. Despite their clinical importance, the mode of quinolone action and mechanisms of resistance are poorly understood at the molecular level. Using a DNA fragment enrichment procedure, we isolated the gyrA gene from a uropathogenic Escherichia coli strain that encodes a gyrase A protein cross-resistant to a variety of quinolones. When complemented with gyrase B subunit, the purified A protein reconstituted DNA supercoiling activity approximately 100-fold more resistant to inhibition by enoxacin than the susceptible enzyme and failed to mediate quinolone-dependent DNA cleavage. Nucleotide sequence analysis revealed that the gene differed at 58 nucleotide positions compared with the K-12 gyrA sequence. The 875-amino-acid residue-resistant gyrase A protein differed at three positions from its wild-type E. coli K-12 counterpart: tryptophan, glutamate, and serine replaced serine, aspartate, and alanine residues at positions 83, 678, and 828, respectively. By genetic analysis of chimeric gyrA genes in a gyrA(Ts) background, we showed that the Ser-83----Trp mutation in the gyrase A protein was solely responsible for high-level bacterial resistance to nalidixic acid and fluoroquinolones.

Analysis of a chimeric class-I patatin-GUS gene in transgenic potato plants: High-level expression in tubers and sucrose-inducible expression in cultured leaf and stem explants

Patatin is a family of lipid acyl hydrolases that accounts for 30 to 40% of the total soluble protein in potato (Solanum tuberosum L.) tubers. To examine the regulation of the patatin genes, we constructed a chimeric gene containing 2.5 kb of 5' flanking sequence from the class I patatin genomic clone PS20 transcriptionally fused to β-glucuronidase (GUS) and introduced it into potato plants using an Agrobacterium tumefaciens Tiplasmid vector. While the chimeric gene was expressed at high levels in tubers and in stolons attached to developing tubers, it was not normally expressed in leaves, stems, roots, or in stolons before tuberizatization. However, the expression of the class I patatin-GUS construct was not "tuber-specific" since leaf and stem explants cultured on medium containing 300 to 400 mM sucrose showed GUS activity equal or greater than that of tubers. The sucrose induction of GUS activity in leaf and stem explants was accompanied by the accumulation of patatin protein and large amounts of starch, but not by the morphological changes that normally are associated with tuberization. In contrast, the GUS reporter gene under the control of the 35S promoter of cauliflower mosaic virus showed an essentially uniform pattern of expression in transgenic potato plants and was not induced by sucrose.

Systemic lymphangiomatosis: a combined diagnostic approach of lymphangiography and computed tomography

A case of systemic lymphangiomatosis in a child is presented and the literature reviewed. Bipedal lymphangiography confirmed the diagnosis by demonstrating bony accumulation of contrast medium, whereas postlymphangiographic computed tomography gave a more accurate assessment of the full extent of bony and visceral involvement.

DNA gyrase complex with DNA: determinants for site-specific DNA breakage

DNA gyrase catalyses DNA supercoiling by making a transient double-stranded DNA break within its 120-150 bp binding site on DNA. Addition of the inhibitor oxolinic acid to the reaction followed by detergent traps a covalent enzyme-DNA intermediate inducing sequence-specific DNA cleavage and revealing potential sites of gyrase action on DNA. We have used site-directed mutagenesis to examine the interaction of Escherichia coli gyrase with its major cleavage site in plasmid pBR322. Point mutations have been identified within a short region encompassing the site of DNA scission that reduce or abolish gyrase cleavage in vitro. Mapping of gyrase cleavage sites in vivo reveals that the pBR322 site has the same structure as seen in vitro and is similarly sensitive to specific point changes. The mutagenesis results demonstrate conclusively that a major determinant for gyrase cleavage resides at the break site itself and agree broadly with consensus sequence studies. The gyrase cleavage sequence alone is not a good substrate, however, and requires one or other arm of flanking DNA for efficient DNA breakage. These results are discussed in relation to the mechanism and structure of the gyrase complex.

Energetics of proline racemase: transition-state fractionation factors for the two protons involved in the catalytic steps

The isotope effects for the interconversion of L-proline and D-proline, catalyzed by proline racemase, have been determined in the saturated region with both [2-2H]proline and [2-3H]proline. The deuterium fractionation factors for each of the protons in flight have been obtained from two kinds of experiment: by measuring the rate of racemization of one [2-2H]proline enantiomer as it racemizes into an equilibrated pool of unlabeled proline and by measuring the deuterium content of a proline sample at the optical rotation maximum that occurs when an equimolar mixture of one deuterium-labeled enantiomer and the other unlabeled enantiomer runs to equilibrium. The tritium fractionation factors for each of the protons in flight have been determined from measurements of the rate of loss of tritium to the solvent as one [2-3H]proline enantiomer runs to equilibrium. Good agreement is found among the fractionation factors determined by each method. The deuterium fractionation factors for the two protons are not identical: that for the proton derived from L-proline is 0.375 and that for the proton derived from D-proline is 0.44. This difference has been confirmed by a double-competition experiment in which the optical rotation of a mixture of DL-[2-2H]proline and unlabeled DL-proline is followed with time. The rotation (initially zero) passes through a maximum, from which the ratio of the two fractionation factors (0.86) is obtained. These data, coupled with the equilibrium fractionation factor for the 2-position of proline (which has been determined to be 1.17), provide the transition-state factors for each of the in-flight protons, and delineate the nature of the transition state(s) for the enzyme-catalyzed racemization.

Energetics of proline racemase: tracer perturbation experiments using [14C]proline that measure the interconversion rate of the two forms of free enzyme

Proline racemase exists in two states, one of which binds and isomerizes L-proline and the other of which binds and isomerizes D-proline. In the enzyme-catalyzed racemization of proline at high substrate concentrations, the interconversion of the two forms of the free enzyme becomes rate limiting. The tracer perturbation method of Britton (1966, 1973) vividly demonstrates the kinetic importance of this enzyme interconversion under oversaturating conditions and allows an estimate of the rate constant for this reaction of 10(5) s-1. It is further shown that the enzyme is bound state saturated and the peak-switch concentration, Cp, is 125 mM. At substrate concentrations higher than 125 mM the enzyme becomes oversaturated, and the reaction rate is limited by the transition state for the interconversion of two forms of the free enzyme. It seems likely that the two free enzyme forms differ only in the protonation states of the acidic and basic groups at the active site.

Energetics of proline racemase: racemization of unlabeled proline in the unsaturated, saturated, and oversaturated regimes

The interconversion of L- and D-proline catalyzed by proline racemase has been studied. The entire time course of the approach to equilibrium has been followed. After a short time the product concentration is significant, and the reaction runs under reversible conditions. As the total substrate concentration is increased, the system moves from the unsaturated regime into the saturated regime. At very high substrate levels under the reversible conditions used, the rate constant for substrate racemization falls, as the system moves into the "oversaturated" regime. Here, the net rate of the enzyme-catalyzed reaction is limited by the rate of return of the free enzyme from the form that liberates product back to the form that binds substrate. The results are analyzed in terms of the simple mechanism (table; see text) and illustrate the additional information that is available from reactions studied under reversible conditions. In the unsaturated region the value of the second-order rate constant kU (equivalent to kcat/Km) is 9 X 10(5) M-1 s-1 in each direction. In the saturated region, kcat = kcat = 2600 s-1 and Km = 2.9 mM. In the oversaturated region, the rate constant kO is 81 M s-1. The substrate concentration at which unsaturated and saturated terms contribute equally is 2.9 mM, and the substrate concentration at which saturated and oversaturated terms contribute equally is 125 mM.

Energetics of proline racemase: rates, fractionation factors, and buffer catalysis in the oversaturated region. Nature of the interconversion of the two forms of free enzyme

To probe the nature of the interconversion of the two unliganded forms of proline racemase, a number of experiments have been performed under oversaturating conditions where the rate of the enzymic reaction is mainly limited by the rate of this interconversion. Competitive deuterium washout experiments, where an equimolar mixture of D- and L-proline (in which some or all of one enantiomer is specifically deuterated at the 2-position) is allowed to reach chemical and isotopic equilibrium mediated by the enzyme, have been followed in four ways. The size and the rate of achievement of the maximum perturbation in the optical rotation have been measured, the deuterium content of the substrate at this maximum has been determined, and the final approach to equilibrium after the perturbation maximum has been followed. Further, the enzyme-catalyzed rate of tritium loss from [2-3H]proline has been established. Finally, it has been shown that the enzyme interconversion reaction is catalyzed by several buffers (such as ammonium, hydrazinium, and hydrogen sulfide). These data are discussed in terms of Marcus' theory, which allows a rather detailed picture of the mechanism of free enzyme interconversion to be drawn. This process nicely parallels the mechanism of the enzyme-catalyzed interconversion of the proline enantiomers, and it is evident that substrate racemization (with the concomitant switch of the enzyme-bound protons) is mirrored by the water-mediated switch of the enzyme-bound protons that effects the interconversion of the free enzyme forms. The results favor a stepwise reaction for the interconversion of the free enzyme forms in which a proton is abstracted from a bound water molecule to give a reaction intermediate having a hydroxide ion bound to the diprotonated form of the enzyme.

Endomyocardial biopsy in pediatric oncology: implications for nursing

At Pacific Presbyterian Medical Center endomyocardial biopsies are utilized in pediatric oncology patients to evaluate the degree of cardiotoxicity resulting from the anthracycline agents doxorubicin and daunorubicin. This article discusses the indications, technical aspects, potential risks and complications of endomyocardial biopsy in pediatric oncology patients. The nursing care of the pediatric patient and family, as well as age-specific teaching guidelines, are described.

Interaction of bleomycin A2 with deoxyribonucleic acid: DNA unwinding and inhibition of bleomycin-induced DNA breakage by cationic thiazole amides related to bleomycin A2

The association of the antitumor antibiotic bleomycin A2 with DNA has been investigated by employing several 2-substituted thiazole-4-carboxamides, structurally related to the cationic terminus of the drug. With a 5'-32P-labeled DNA restriction fragment from plasmid pBR322 as substrate, these compounds have been shown to inhibit bleomycin-induced DNA breakage. Analogues possessing 2'-aromatic substituents on the bithiazole ring were more potent inhibitors than those carrying 2'-aliphatic groups, e.g., the acetyl dipeptide A2. The degree of inhibition was similar at all scission sites on DNA, and inclusion of the analogues did not induce bleomycin cleavage at new sites. DNA binding of bithiazole derivatives has also been studied by two complementary topological methods. Two-dimensional gel electrophoresis using a population of DNA topoisomers and DNA relaxation experiments involving calf thymus DNA topoisomerase I and pBR322 DNA reveal that bleomycin bithiazole analogues unwind closed circular duplex DNA. The inhibition and unwinding studies together support recent NMR studies suggesting that both bleomycin A2 and synthetic bithiazole derivatives bind to DNA by an intercalative mechanism. The results are discussed in relation to the DNA breakage properties of bleomycin A2.

DNase I hypersensitive sites in the chromatin of human mu immunoglobulin heavy-chain genes

An immunoglobulin polypeptide chain is encoded by multiple gene segments that lie far apart in germ-line DNA and must be brought together to allow expression of an immunoglobulin gene active in B lymphocytes. For the immunoglobulin heavy chain genes, one of many variable (V) region genes becomes joined to one of several diversity (D) segments which are fused to one of several joining (J) segments lying 5' of the constant region (C) genes. Here we show that the rearranged mu genes of an IgM-producing human B-lymphocyte cell line exhibit pancreatic deoxyribonuclease (DNase I) hypersensitive sites in the JH-C mu intron that are absent in naked DNA or the chromatin of other differentiated cell types. DNA sequence analysis reveals that the major hypersensitive site maps to a conserved region of the JH-C mu intron recently shown to function as a tissue-specific enhancer of heavy-chain gene expression. A similar association of an enhancer-like element with a DNase I hypersensitive site has been reported for the mouse immunoglobulin light-chain J kappa-C kappa intron. These results implicate disruption of local chromatin structure in the mechanism of immunoglobulin enhancer function.

Fibrinolytic effects of intracoronary streptokinase administration in patients with acute myocardial infarction and coronary insufficiency

Serial coagulation studies were obtained in 25 patients treated with intracoronary streptokinase infusion for myocardial infarction (23 patients) or coronary insufficiency (two patients) to determine the frequency of systemic fibrinolytic activity. Clotting studies were obtained before and after infusion and at 4-hour intervals until normalization. Intracoronary thrombolysis was successful in 20 of 23 patients (87%) with myocardial infarction. Streptokinase dosage in this study was 201,000 +/- 74,000 IU (+/- SD). Systemic fibrinolytic activity, defined as greater than 70% reduction of fibrinogen using a functional assay (Claus method), occurred in 22 of 25 patients (88%) and was present at a mean streptokinase dosage of 119,000 +/- 52,000 IU. Fibrinogen in the total population decreased from 342 +/- 80 to 87 +/- 94 mg% (p less than 0.0001). In patients with systemic effect, the mean fibrinogen level after infusion was 17% of baseline, increased to 43% at 24 hours, and returned to normal at 30 hours. Plasminogen decreased to 7% of baseline activity after infusion (p less than 0.0001), was 44% of baseline at 24 hours, and returned to normal at 48 hours. Intraprocedural sampling during infusion showed reduction of fibrinogen by 25% after 30,000 IU (p less than 0.0005) and by 71% at 120,000 IU (p less than 0.0001); plasminogen decreased by 50% after 30,000 IU (p less than 0.0001) and by 84% at 120,000 IU (p less than 0.0001). Prothrombin time increased from 11.5 +/- 0.8 seconds to 22.0 +/- 7.8 seconds after infusion (p less than 0.0001) and returned to normal at a mean of 18 +/- 11 hours after infusion. Partial thromboplastin time was markedly prolonged (greater than 100 seconds) after infusion, returned to less than or equal to 2 times control at 5 +/- 2 hours, and returned to normal at 9 +/- 4 hours after infusion. Fibrinogen degradation products were less than 10 micrograms/ml before infusion, increased to greater than 40 micrograms/ml after infusion, and remained greater than 40 micrograms/ml in 40% of patients at 24 hours after infusion. These data indicate that systemic fibrinolytic activity occurs in a high percentage of patients with "low-dose" intracoronary streptokinase infusion and that coagulation variables may be altered for 24-48 hours after infusion.

Site-specific interaction of DNA gyrase with DNA

DNA gyrase, in the presence of the inhibitor oxolinic acid, can induce double-strand DNA breakage at specific sites. The sequences at several sites have been determined. In addition, the structure of complexes formed between DNA gyrase and restriction fragments containing an oxolinic acid-promoted cleavage site has been examined by DNase protection methods. DNA gyrase protects more than 120 base pairs of DNA against pancreatic DNase in a region surrounding the cleavage site. Protection is observed both in the presence and absence of oxolinic acid. Protected DNA flanking the cleavage site contains DNase I-sensitive sites spaced on the average 10 or 11 base pairs apart. This result supports the view that, in the DNA gyrase--DNA complex, the DNA is largely wrapped on the outside of the enzyme.

Recovery of Chlamydia trachomatis from patients of southeastern venereal disease clinic

The authors determined the incidences of Chlamydia trachomatis colonization obtained by use of two methods of isolation in 169 specimens from individuals attending a venereal disease clinic. Speciments were collected in phosphate sucrose buffer and planted simultaneously onto McCoy cells previously treated with 5-iodo-2-deoxyuridine (IUDR) and with cycloheximide. As controls, specimens were obtained from 76 hospital employees or medical students without clinical signs of infection and cultured in a similar manner. Qualitatively, recoveries of Chlamydia trachomatis inclusions from the differently treated cells were the same, but the number of inclusions per ml was greater for the cycloheximide-treated cells. Recoveries of Chlamydia trachomatis from the venereal disease clinic population were 33% for those patients who also had simultaneous culture positive for Neisseria gonorrhoeae and 42% for those with nongonococcal urethritis. The recovery of Chlamydia trachomatis from the control group was 5%.

DNA gyrase action involves the introduction of transient double-strand breaks into DNA

DNA gyrase from Escherichia coli, in the presence of ATP, can both separate catenated DNA circles and unknot knotted DNA. Both these reactions require passage of a DNA segment through a transient double-strand break in DNA. Evidence that transient double-strand breaks are also involved in the supercoiling and relaxing activities of DNA gyrase is derived from experiments showing that the linking number of circular DNA is changed in steps of two. A mechanism is proposed for the action of the enzyme.

DNA gyrase: purification and catalytic properties of a fragment of gyrase B protein

A protein isolated from Escherichia coli complements the DNA gyrase A (NalA) protein to generate an activity that relaxes supercoiled DNA. Oxolinic acid, a known inhibitor of DNA gyrase, blocks this activity and causes double-strand cleavage of DNA at the same sites as are attacked by DNA gyrase. The protein, of molecular weight 50,000, appears to be fragment of the DNA gyrase B (Cou) protein (molecular weight, 90,000) as judged by the identical sizes of numerous peptides produced by partial proteolytic digestion. The complex of this fragment and the gyrase A protein lacks both the DNA-supercoiling and DNA-dependent ATPase activities of DNA gyrase.

Energetics of triosephosphate isomerase: the nature of the proton transfer between the catalytic base and solvent water

The isomerization of specifically deuterium-labeled [1(R)-2H5dihydroxyacetone phosphate to D-glyceraldehyde 3-phosphate, catalyzed by the enzyme triosephosphate isomerase, has been studied. It is shown that the extent of transfer of the 2H label from the substrate to the product D-glyceraldehyde 3-phosphate is (after complete reaction) the same as that of the corresponding transfer of 3H. The absence of an isotope effect shows that the exchange process of the tstopically labeled enzyme carboxyl group, -COOL H2O leads to -COOH + LOH, does not tnvolve a rate-limiting transition state in which L is the flight. Possible modes for the nature of the ionization of -COOL in 1H2O are discussed.

Partial isolation and translation in vitro of messenger ribonucleic acid for phosphoenolpyruvate carboxykinase (guanosine triphosphate)

1. mRNA was extracted from the livers of starved rats and incubated in a heterologous cell-free protein-synthesizing system derived from rabbit reticulocytes. The presence of newly synthesized phosphoenolpyruvate carboxykinase (GTP) was detected by immunoprecipitation with a specific antibody to the enzyme and analysis by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 2. The synthesis of the enzyme was dependent on the addition of rat liver RNA, whereas RNA isolated from rat spleen was inactive. If ovalbumin and anti-ovalbumin were used to form the immunoprecipitates, no radioactivity that migrated as phosphoenolpyruvate carboxykinase was detected. 3. The optimal concentrations of magnesium acetate and KCl for phosphoenolpyruvate carboxykinase synthesis were determined. 4. When polyribosomal RNA was separated by sucrose-gradient centrifugation, phosphoenolpyruvate carboxykinase mRNA migrated between 20 and 26 S in keeping with the high mol. wt. of the protein (85 000). 5. The presence of poly(A) in phosphoenolpyruvate carboxykinase mRNA was suggested by retention of mRNA activity on oligo(dT)-cellulose columns. 6. It was concluded that the cell-free synthesis of phosphoenolpyruvate carboxykinase can serve as a bioassay for intracellular phosphoenolpyruvate carboxykinase mRNA.

Deinduction of phosphoenolpyruvate carboxykinase (guanosine triphosphate) synthesis in Reuber H-35 cells

The activity of phosphoenolpyruvate carboxykinase (GTP) in Reuber H-35 cells was decreased after the removal of 6-N,2-O-dibutyryl adenosine 3':5'-monophosphate (dibutyryl cyclic AMP) from the medium. The decrease in activity was shown immunochemically to be the result of a rapid cessation in specific enzyme synthesis, occurring with a half-time of 40 min. The removal of dexamethasone, a less potent inducer of the enzyme in these cells, did not effect the activity of P-enolpyruvate carboxykinase or its rate of synthesis. Insulin added to either dibutyryl cyclic AMP or dexamethasone-treated cells produced a decline in specific enzyme synthesis which was not as rapid as that observed upon removal of dibutyryl cyclic AMP. This effect of insulin did not require the presence of glucose in the culture medium. Estimates of the half-life of the mRNA for P-enolpyruvate carboxykinase using actinomycin D and cordycepin suggested that after the inhibition of transcription of mRNA, enzyme synthesis continued for periods considerably longer than that observed after deinduction caused by removal of dibutyryl cyclic AMP. In addition, the synthesis of the enzyme could be restimulated by dibutyryl cyclic AMP in the absence of RNA synthesis. It was proposed that the deinduction of phosphoenolpyruvate carboxykinase in these cells is being regulated at the post-transcriptional or translational level.

Acute hepatic coma successfully treated by extracorporeal baboon liver perfusions

Two patients in deep hepatic coma due to fulminant viral hepatitis were treated by extracorporeal baboon liver perfusion after failing to respond to medical treatment and three consecutive exchange transfusions. Both patients recovered full consciousness after one liver perfusion, made a complete recovery, and were leading normal lives seven and eight months after treatment. Perfusions were maintained for 13(1/2) and 16(1/2) hours without complication, and neither clinical immunological reactions nor antibaboon serum antibodies developed as a result of treatment.Whereas normal consciousness could be restored only by liver perfusion, both exchange transfusion and liver perfusion were effective in clearing bilirubin and in raising the level of clotting factors. Extracorporeal baboon liver perfusion provides a safe and effective method for the treatment of acute hepatic coma.