Determination of microdialysis extraction fraction of cocaine by the no net flux method under high, low, and zero steady-state cocaine concentrations in rats

The effect of different steady-state cocaine concentration maintenance on the microdialysis extraction fraction of cocaine (in situ recovery; Ed) in the medial prefrontal cortex (mPFC) was examined. Male, adult Sprague-Dawley rats anesthetized with chloral hydrate were used. All rats were randomly divided into three groups and were given cocaine i.v. infusion of either 0.6 mg/kg/min (group A), 0.3 mg/kg/min (group B), or 0.0 mg/kg/min (group C). A steady-state cocaine concentration in the blood was obtained for both A and B groups. They were 24.3 +/- 2.3 microM, respectively. We then applied the no net flux microdialysis method to determine the Ed of cocaine in vivo for all three groups. Results revealed that there was no significant difference of Ed under these three different infusion regimens (group A: 16 +/- 2%; group B: 17 +/- 1%; group C: 21 +/- 2%). The steady-state cocaine concentration in the mPFC was also estimated to be 17.7 +/- 1.3 microM, 11.3 +/- 2.0 microM, and 0.7 +/- 0.6 microM, respectively. We then concluded that the Ed of cocaine in the mPFC is invariable while the steady-state cocaine concentration in the mPFC was ranging from 0 to 18 microM. This information is useful in the cocaine pharmacokinetic study since scientists are concerned about the variations of Ed while cocaine concentration in the mPFC is changing.

Self-association of Escherichia coli DNA-dependent RNA polymerase core enzyme

The extent of self-association of Escherichia coli DNA-dependent RNA polymerase core enzyme has been investigated by velocity sedimentation as a function of both NaCl and protein concentrations. The core enzyme, existing as essentially monomeric species having a sedimentation coefficient of 13.1 S at NaCl concentrations greater than 0.2 M, undergoes reversible self-association at lower salt concentrations. Estimates for the stoichiometry of association and equilibrium constants of reaction were determined from the effect of protein concentration on the weight-average sedimentation coefficient measured at different NaCl concentrations. Data analysis by a nonlinear curve-fitting procedure indicated that protein self-association is best described by a sequential model characterized by weaker association constants for each additional step of oligomerization, and any model that involves cooperative formation of oligomeric species can be excluded. These findings are at variance with the conclusion of a previous study [Shaner, S. L., Platt, D. M., Wensley, C. G., Yu, H., Burgess, R. R., & Record, M. T. (1982) Biochemistry 26, 5539-5551] which suggested that core RNA polymerase exists in equilibrium between monomeric and tetrameric forms of the enzyme and excluded the existence of intermediate species. Simulation of sedimentation velocity boundary and gradient profiles are used to assess the validity of both models of association of core protein. It was clear that had the core enzyme undergone a cooperative monomer<-->tetramer mode of association, then bimodality would have been observed in the derivative tracings of the sedimentation boundary under these experimental conditions. Nevertheless, no such observation was reported by Shaner et al. and this study. The sequential model favored by the results of this study is consistent with the proposed model resulted from a small-angle X-ray study [Heumann, H, Meisenberger O., & Pilz, I. (1982) FEBS Lett. 138, 273-276]. Further analysis of the data by the Wyman linked-function relationship [Wyman, J. (1964) Adv. Protein Chem. 19, 223-286] implies that core enzyme monomer loses approximately three counterions per contact upon association to higher oligomeric species.

Transplantation of CD34+ peripheral blood progenitor cells after high-dose chemotherapy for patients with advanced multiple myeloma

A major potential problem of autologous transplantation in the treatment of advanced malignancy is the infusion of tumor cells. A multi-institutional study of purified CD34-selected peripheral blood progenitor cell (PBPC) transplantation was conducted in 37 patients with advanced multiple myeloma receiving myeloablative chemotherapy. Fourteen days after intermediate-dose cyclophosphamide, prednisone, and granulocyte colony-stimulating factor (G-CSF), a median of 3 (range, 2 to 5) 10-L leukaphereses yielded 9.8 x 10(8)/kg (range, 3.7 to 28.3) mononuclear cells. The adsorbed (column-bound) fraction contained 5.9 x 10(6) cells/kg (range, 1.6 to 25.5) with 4.65 x 10(6) CD34 cells/kg (range, 1.2 to 23.3). Using Poisson distribution analysis of positive polymerase chain reactions with patient-specific complementarity-determining region 1 (CDR1) and CDR3 Ig-gene primers, tumor was detected in leukapheresis products from 8 to 14 unselected patients and ranged from 1.13 x 10(4) to 2.14 x 10(6) malignant cells/kg. After CD34 selection, residual tumor was detected in only three patients' products. Overall, a greater than 2.7- to 4.5-log reduction in contaminating multiple myeloma cells was achieved. CD34 PBPCs were infused 1 day after busulfan (14 mg/kg) and cyclophosphamide (120 mg/kg), and granulocyte-macrophage colony-stimulating factor was used until hematologic recovery. The median time to both neutrophil and platelet recovery was 12 days (range, 11 to 16 days and 9 to 52 days, respectively). The median number of erythrocyte and platelet transfusions was 7 (range, 2 to 37) and 3 (range, 0 to 85), respectively. Patients receiving fewer than 2 x 10(6) CD34 cells/kg had significantly prolonged neutropenia, thrombocytopenia, and an increased red blood cell and platelet transfusion requirement. Thus, CD34 selection of PBPCs markedly reduces tumor contamination in multiple myeloma and provides effective hematopoietic support for patients receiving myeloablative therapy.

Cryopreservation and semen quality in patients with Hodgkin's disease

BACKGROUND

Cryopreservation of semen from patients with Hodgkin's disease yields fewer motile sperm than from fertile men without Hodgkin's disease. However, although poor sperm quality and subfertility have been associated with Hodgkin's disease, whether the disease adversely affects sperm quality is not clear because many studies evaluated semen quality after chemotherapy or radiation therapy had begun. Furthermore, the effect of cryopreservation on semen quality in these patients is unknown. This study investigated pretreatment sperm quality and the effect of cryopreservation on semen quality in patients with Hodgkin's disease.

METHODS

Specimens from 39 patients with Hodgkin's disease and 30 normal volunteers who underwent sperm banking over a 5-year period were analyzed. No patient had undergone chemotherapy or radiation therapy before sperm banking. The nitrogen vapor technique, using Test-Yolk buffer with glycerol as a cryoprotective agent, was used for cryopreservation. Prefreeze and postthaw motile sperm count (MSC) and motion characteristics, namely motility, curvilinear velocity (VCL), linearity, amplitude of lateral head movement (ALH), and motility index, were compared between the two groups.

RESULTS

Prefreeze values for MSC (P = 0.0001), motility (P = 0.0001), motility index (P = 0.0001), and VCL (P = 0.0019) differed significantly between patients and donors. Except for linearity and ALH, postthaw sperm MSC, motility, VCL, and motility index decreased significantly (P = 0.0001) in both groups. However, the percentage decline in semen quality from prefreeze to postthaw values did not differ significantly between donors and patients.

CONCLUSION

The pretreatment semen quality in patients with Hodgkin's disease is poor compared with that of normal fertile men. However, half the patients had a normal MSC, so a clinical diagnosis of Hodgkin's disease does not predict cryopreservation outcome adequately. Semen cryopreservation should be encouraged as a routine part of the therapeutic management of men of reproductive age who will undergo chemotherapy or radiation therapy for Hodgkin's disease.

Activation of Ca(2+)-calmodulin-dependent protein kinase Ia is due to direct phosphorylation by its activator

Ca(2+)-Calmodulin-dependent protein kinase Ia (CaM kinase Ia) is phosphorylated, and its activity enhanced up to 50-fold, in the presence of a protein purified from pig brain termed CaM kinase Ia activator [Lee, J.C. and Edelman, A.M. (1994) J. Biol. Chem. 269, 2158-2164]. We report here that phosphorylation of CaM kinase Ia in the presence of the activator occurs primarily on threonine (87%) and slightly on serine (13%) residues. Treatment of CaM kinase Ia with the irreversible ATP affinity analogue, 5'-p-fluorosulfonylbenzoyl adenosine (FSBA), reduces its activity by 86% but has no effect on its ability to be phosphorylated, whereas FSBA-treatment of the activator reduces its ability to activate and phosphorylate CaM kinase Ia by 92 and 93%, respectively. Thus, CaM kinase Ia activator is a protein Thr/Ser kinase which activates by phosphorylating CaM kinase Ia rather than by enhancing the latter's autophosphorylation.

KR-25003, a potent analgesic capsaicinoid

The crystal structure of N-[3-(3,4-dimethylphenyl)propyl] (4-hydroxy-3-methoxyphenyl)acetamide, C20H25NO3, was determined to a final R value of 0.047. The vanilloid, amide and dimethylphenyl groups of the compound are nearly perpendicular with respect to one another. The overall conformation in the crystalline state is somewhat different from that of other capsaicinoids. The molecules are stabilized by intermolecular hydrogen bonds.

SB 203580 is a specific inhibitor of a MAP kinase homologue which is stimulated by cellular stresses and interleukin-1

A class of pyridinyl imidazoles inhibit the MAP kinase homologue, termed here reactivating kinase (RK) [Lee et al. (1994) Nature 372, 739-746]. We now show that one of these compounds (SB 203580) inhibits RK in vitro (IC50 = 0.6 microM), suppresses the activation of MAPKAP kinase-2 and prevents the phosphorylation of heat shock protein (HSP) 27 in response to interleukin-1, cellular stresses and bacterial endotoxin in vivo. These results establish that MAPKAP kinase-2 is a physiological RK substrate, and that HSP27 is phosphorylated by MAPKAP kinase-2 in vivo. The specificity of SB 203580 was indicated by its failure to inhibit 12 other protein kinases in vitro, and by its lack of effect on the activation of RK kinase and other MAP kinase cascades in vivo. We suggest that SB 203580 will be useful for identifying other physiological roles and targets of RK and MAPKAP kinase-2.

Increased expression of cell adhesion molecule P-selectin in active inflammatory bowel disease

The pathogenic changes of inflammatory bowel disease (IBD) depend on migration of circulating leucocytes into intestinal tissues. Although leucocyte rolling and tenuous adhesion are probably regulated by inducible selectins on vascular endothelia, little is known about the expression of these molecules in Crohn's disease and ulcerative colitis. Using immunohistochemistry on surgically resected specimens, this study investigated endothelial P-selectin (CD62, granular membrane protein-140) in frozen sections of histologically uninvolved tissues adjacent to inflammation (Crohn's disease = 10; ulcerative colitis = 10), from highly inflamed areas (Crohn's disease = 20; ulcerative colitis = 13), and from normal bowel (n = 20). By light microscopy, two forms of P-selectin immunoreactivity were detected that apparently corresponded ultrastructurally to stored and released distributions. Compared with the normal gut, there was a 3.7-fold increase of P-selectin immunoreactivity on veins (p < 0.0001), venules (p < 0.0001), and capillaries (p < 0.05) in the highly inflamed gut, without differences between Crohn's disease and ulcerative colitis. In the uninvolved gut, P-selectin expression was similar to that seen in normal controls, except for a focal increase of P-selectin in the vicinity of small lymphocyte aggregates. The dramatic upregulation of P-selectin in the inflamed tissue and its potential role in leucocyte trafficking support the concept of P-selectin blocking therapy for the control of active IBD.

Contributions of multiple basic amino acids in the C-terminal region of yeast ribosomal protein L1 to 5 S rRNA binding and 60 S ribosome stability

Previous studies suggest that the C-terminal region of ribosomal protein L1 from Saccharomyces cerevisiae is important for its interaction with the 5 S rRNA molecule. Within this region are several highly conserved basic amino acids including Lys276, Lys279, Lys289, Arg282, Arg285. To examine potential contributions of these amino acids to RNA-protein interaction and ribosomal assembly, effects of substitutions of these residues by methionine either individually or in combinations were examined. A methionine substitution of any one of the lysine residues did not significantly affect RNA binding in vitro. The mutant RNPs were as stable as the wild-type RNP. Yeast transformants expressing these mutant proteins grew at the same rate as the wild-type. However, mutant proteins containing substitutions of any two of these basic amino acids bound RNA weakly. The resultant RNPs were significantly less stable than the wild-type. Whereas cells expressing mutant L1 with a single substitution at 289 was not lethal, cells expressing mutant L1 with any double substitutions involving Lys289 as one of the substituted amino acids were lethal. These data suggest that Lys289 plays a key role in the binding of ribosomal protein L1 to 5 S rRNA. The other basic residues, particularly Arg282, and Arg285, in this region also contribute to RNA binding. These residues are predicted to locate on the same side of an alpha helix. We would like to propose a structural model for the yeast RNP that involves multiple contact sites located on one side of the helix in the C terminus of the protein and the 5 S rRNA. These basic amino acids also participate, directly or indirectly, in the interaction of the RNP complex with other components of the 60 S ribosomal subunit.

Antineutrophil antibodies in familial inflammatory bowel disease

BACKGROUND/AIMS

Antineutrophil cytoplasmic antibodies have been reported to occur more frequently in healthy first-degree relatives of patients with ulcerative colitis than in healthy controls. The aim of this study was to determine their prevalence in families in which more than one member was affected with inflammatory bowel disease.

METHODS

With use of an indirect immunofluorescence method, 168 affected members and 197 unaffected first-degree relatives in 56 such families were studied.

RESULTS

Antibodies were detected in 46% of patients with ulcerative colitis without a positive family history and in 44% of those within families with several affected members. There was no evidence of clustering of antibodies in particular families. Within families in which both ulcerative colitis and Crohn's disease coexisted, antibodies were detected primarily in patients with ulcerative colitis. Antibodies were seldom present (3%) in those patients with Crohn's disease, whether they were familial or nonfamilial cases. Similarly, antibodies were seldom present (3%) in controls or the unaffected first-degree relatives of patients with inflammatory bowel disease.

CONCLUSIONS

Antineutrophil cytoplasmic antibodies are associated with ulcerative colitis, and their presence is not increased in the first-degree relatives of patients with ulcerative colitis. They are more likely to be a consequence of the disease than a subclinical genetic disease marker.

Effect of cyclic phenyl saligenin phosphate and paraoxon treatment on vascular response to adrenergic and cholinergic agents in hens

The response of peripheral blood vessels to adrenergic and cholinergic agonists was examined 1, 3, 7, and 21 d after hens were treated with a single intramuscular injection of 2.5 mg/kg cyclic phenyl saligenin phosphate (PSP) or 0.10 mg/kg paraoxon (PXN). These two organophosphates (OPs) cause different clinical effects in exposed animals, as PSP causes organophosphate-induced delayed neuropathy (OPIDN) and PXN causes acute poisoning through inhibition of acetylcholinesterase. For these studies, the ischiadic artery was cannulated both prograde and retrograde and the blood was shunted through a pump to maintain a constant flow. Alterations in pressure measured at the pump outflow were used to indicate changes in limb vascular resistance. Dose-response curves were generated for the response to intravenous administration of acetylcholine (ACh), phenylephrine (PE), or salbutamol (SAL) (10(-8) to 10(-4) mol/kg). Acetylcholine at 10(-8) to 10(-7) mol/kg caused an increase in vascular resistance, whereas concentrations of 10(-5) to 10(-4) mol/kg caused a decrease in vascular resistance in hens given PSP 1 and 3 d previously. The response of PXN-treated hens to ACh was not significantly altered from that of vehicle-treated hens. The resistance generated in response to PE, an alpha 1-adrenergic agonist, in PSP-treated hens was greater than levels in vehicle-treated hens on d 1 and 3 and greater than the response seen in hens treated with PXN. Salbutamol, a beta 2-adrenergic agonist, at concentrations of 10(-7) to 10(-4) mol/kg caused an increase in resistance 1 and 3 d after PSP and a decrease on d 7. The responses to SAL were different in PXN-treated hens, as these hens demonstrated a lesser increase in resistance at concentrations of 10(-8) to 10(-7) mol/kg and a decrease in resistance at 10(-5) to 10(-4) mol/kg 1 d after administration of PXN. These observations indicate that response to vasoactive agents is altered in OP-treated hens and that responses differ between a compound capable of causing OPIDN (PSP) and a compound that only causes acute effects (PXN).

Antibodies to capsular polysaccharides are not protective against experimental Staphylococcus aureus endocarditis

The protective efficacy of antibodies to the Staphylococcus aureus capsular polysaccharide was examined in a rat model of catheter-induced endocarditis. Capsular antibodies were induced either by active immunization with killed S. aureus or by passive immunization with hyperimmune rabbit antiserum to S. aureus. Control rats were injected with phosphate-buffered saline or passively immunized with normal rabbit serum or rabbit antiserum to a nonencapsulated strain. Animals with indwelling catheters were challenged intravenously with 5 x 10(4) to 4 x 10(6) CFU of the homologous S. aureus strain (capsular serotype 5 strain Reynolds or serotype 1 strain SA1 mucoid). Both immunized and control rats developed S. aureus endocarditis. The numbers of S. aureus cells recovered from the blood and aortic valve vegetations of immunized rats were similar to those of control rats, indicating that capsule-specific antibodies were not protective. To determine whether the presence of an indwelling catheter interfered with antibody-mediated protection against S. aureus endocarditis, catheters were removed 2 h after insertion in additional groups of rats. An inoculum of 10(8) CFU of strain Reynolds was needed to provoke endocarditis in rats catheterized for 2 h, compared with 5 x 10(4) CFU for rats with indwelling catheters. Passively transferred capsular antibodies were not protective since both immunized and nonimmunized animals developed endocarditis, and quantitative cultures of blood and valvular vegetations revealed no differences between immunized and control animals. The findings of this study indicate that antibodies to the capsular polysaccharide are not protective in the rat model of experimental S. aureus endocarditis.

Involvement of Neurospora mitochondrial tyrosyl-tRNA synthetase in RNA splicing. A new method for purifying the protein and characterization of physical and enzymatic properties pertinent to splicing

The Neurospora CYT-18 protein, the mitochondrial tyrosyl-tRNA synthetase, functions in the splicing of group I introns. Here, bacterially expressed CYT-18 protein, purified by a new procedure involving polyethyleneimine precipitation to remove tightly bound nucleic acids, was used to characterize properties pertinent to RNA splicing. Analytical ultracentrifugation and other methods showed that the CYT-18 protein is an asymmetric homodimer. The measured frictional ratio, f/fo = 1.55, corresponds to an axial ratio of 10 for a prolate ellipsoid or 12 for an oblate ellipsoid. Like bacterial TyrRSs, the CYT-18 protein exhibits half-sites reactivity, each homodimer having one active site for tyrosyl adenylation and RNA splicing. The splicing activity of CYT-18 was unaffected by aminoacylation substrates at concentrations used in aminoacylation reactions, whereas the TyrRS activity was inhibited by physiological concentrations of the splicing cofactor GTP, as well as CTP or UTP, or by low concentrations of a group I intron RNA. Kinetic measurements suggest that the binding of CYT-18 to a group I intron substrate is a two-step process, with an initial biomolecular step that is close to diffusion limited (3.24 +/- 0.03 x 10(7) M-1s-1) followed by a slower conformational change (0.54 +/- 0.07 s-1). After CYT-18 binding, splicing occurs at a rate of 0.0025 s-1, within 6-fold of the rate of self-splicing of the Tetrahymena large rRNA intron in vitro. The Kd for the complex between the CYT-18 protein and a group I intron substrate, calculated from koff/kon, was < 0.3 pM, substantially lower than determined by presumed equilibrium measurements [Guo, Q., & Lambowitz, A. M. (1992) Genes Dev. 6, 1357-1372]. As a result of this tight binding, the CYT-18 protein functions stoichiometrically in in vitro splicing reactions due to its extremely slow dissociation from the excised intron RNA. The very tight binding of the CYT-18 protein to the intron RNA raises the possibility that specific mechanisms exist for dissociating the protein from the excised intron in vivo.

An in vitro system for studying RNA-protein interaction: application to a study of yeast ribosomal protein L1 binding to 5S rRNA

Previous attempts to study the binding of yeast ribosomal protein L1 with 5S rRNA in vitro have been impeded by the failure to form RNA-protein complexes with purified protein and RNA. To circumvent this difficulty, we have developed an in vitro system that allowed RNP formation. The system involved in vitro expression of the protein L1 from its cloned gene in the presence of exogenous yeast 5S rRNA. A protein of the expected size (34 kDa) was synthesized by in vitro transcription and translation. A specific 5S rRNA-protein L1 complex (RNP) was formed when the rRNA molecule was present during protein L1 synthesis. However, the full-length protein L1 failed to bind 5S rRNA. The extent of RNP formation was proportional to the concentration of the exogenous yeast 5S rRNA in the reaction. The RNP displayed properties identical to those isolated from mature 60S ribosome subunits. Addition of yeast 5.8S rRNA did not result in the formation of a specific RNP. Using this in vitro system, we examined the ability of several deletion mutant proteins to bind yeast 5S rRNA and concluded that protein L1 missing residues 261 to 295 from the C-terminus could not bind yeast 5S rRNA. This in vitro system should be useful for future studies on the molecular nature of 5S rRNA-protein L1 interaction.

The institutionalization of public hygiene in Korea, 1876-1910

On the whole, the major impetus for the institutionalization of public hygiene in Korea came from two directions. On one hand, the self-enlightened intellectuals had introduced a variety of Western ideas and theories on public hygiene since the mid-eighteenth century. On the other hand, Japan strongly influenced the modern systems of Korean health care and medical education, especially through Japanese efforts at the sanitary control of infectious diseses such as smallpox and cholera. The institutionalization of Korea's public hygiene in this period corresponded not to the high ideas of the progressive intellectuals but to the larger social and institutional changes caused by the major political events. Ideas of public hygiene were institutionalized as a powerful strategy of linking the imperial capital and colonial domains.

Fine-needle aspiration cytologic diagnosis of lymphoepithelioma-like carcinoma of the lung. Report of two cases with immunohistochemical study

Lymphoepithelioma is a term used to describe an undifferentiated carcinoma with prominent lymphoid infiltration in the nasopharynx. Recently, tumors with similar histology, designated as lymphoepithelioma-like carcinomas, have been described in other sites including the lung. The authors report two cases of pulmonary lymphoepithelioma-like carcinoma that were correctly diagnosed by fine-needle aspiration cytology. The distinctive cytologic features consist of cohesive sheets and clusters of spindle tumor cells, which possess moderately pleomorphic vesicular nuclei and prominent nucleoli that are intimately intermixed with numerous small lymphocytes. Immunohistochemical study, performed on the cell block preparation, revealed strong positive staining of these tumor cells for epithelial markers. In both cases, the cytologic diagnosis were confirmed subsequently by histologic examination of the resected surgical specimens. Cytologically, the differential diagnoses include granulomatous inflammatory diseases (especially tuberculosis), malignant lymphoma, melanoma, and metastatic sarcoma. The characteristic cytology of the tumor cells, together with their pattern of immunohistochemical staining, are helpful to distinguish lymphoepithelioma-like carcinoma from the differential diagnoses. In these cases, careful examination of the nasopharynx, preferably with multiple random mucosal biopsies, is essential for the exclusion of nasopharyngeal undifferentiated carcinoma because of the obvious differences in treatment and prognosis.

[Understanding American health care reform, 1910-1932: toward an interpretive history of health policy]

The purpose of this article is to analyze the two early health care reform groups: the American Association for Labor Legislation (AALL), the first organization to try to initiate compulsory health insurance in the U.S., and the Committee on the Costs of Medical Care (CCMC), a self-formed committee to study the economics of medical care. By viewing health policy from a historical perspective, we can find a variety of possible alternatives that would have been implemented in different place and time. Unlike positivistic studies on health policy whose only concern is with successful programs, the history of health policy is interested not only in success but also in failure of policy. Reformers from the late 1910s through early 1930s recognized health insurance as a medical issue not as a welfare issue. As long as health insurance belonged to medical domain, policy on health insurance remained separate from public policy. If so, who analyzed and decided the policy? This article argues that social reformers in this period should have tried to launch health insurance not from the front of medical care but in the field of public welfare. This shift in the direction of health care reform would inevitably have caused changes in the strategies accepted.

A protein kinase involved in the regulation of inflammatory cytokine biosynthesis

Production of interleukin-1 and tumour necrosis factor from stimulated human monocytes is inhibited by a new series of pyridinyl-imidazole compounds. Using radiolabelled and radio-photoaffinity-labelled chemical probes, the target of these compounds was identified as a pair of closely related mitogen-activated protein kinase homologues, termed CSBPs. Binding of the pyridinyl-imidazole compounds inhibited CSBP kinase activity and could be directly correlated with their ability to inhibit cytokine production, suggesting that the CSBPs are critical for cytokine production.

Absolute requirement of cyclic nucleotide in the activation of the G141Q mutant cAMP receptor protein from Escherichia coli

cAMP receptor protein (CRP), when interacting with cAMP, controls the expression of a network of catabolite-sensitive genes in Escherichia coli. To understand the molecular events that lead to the activation of CRP, a combined approach of site-directed mutagenesis and thermodynamic analysis was employed to study a member of a specific class of CRP mutant, CRP, which activates the in vivo expression of CRP-dependent operons in cya- strains in the absence of exogenous cAMP. Results from in vitro studies show that the CRP mutant G141Q absolutely requires cAMP for interacting with specific DNA. A quantitative comparison of the thermodynamic parameters governing ligand binding and DNA-protein complex formation in the presence of different cyclic nucleotides leads to the conclusion that this CRP mutant is activated only in the presence of cyclic nucleotides. The specificity toward cyclic nucleotides exhibited by wild-type CRP is lost in this mutant. Furthermore, the binding affinity of the ligand for the first binding site of the mutant is essentially the same as that of wild-type CRP regardless of the identity of the cyclic nucleotide. Hence, the observed in vivo activation of CRP-dependent operons by G141Q in the absence of exogenous cAMP is most likely the consequence of the replacement of cAMP by other cyclic nucleotides to activate the mutant. It is also possible that trace levels of cAMP present in the cya- strain could account for the in vivo activation of the mutant. Furthermore, these results indicate that this CRP mutant does not assume the activated conformation in the absence of cyclic nucleotides, in contrast to the current model derived from results of in vivo studies.

Torsional performance of canine femoral osteotomy union

This study allows the establishment of a protocol for standardizing the technical methodology of canine surgery for mechanical testing. Twenty mongrels were divided into 4 groups of 5 dogs each. All dogs had one femur selected as the test bone and the contralateral as paired control. The test femur was osteotomized and plated. The dogs were sacrificed at 7, 10, 13 and 16 weeks according to their group designation to determine healing of the osteotomy. Both test and control femora were tested to fracture in torsion using a computerized torsion machine. Various mechanical parameters were studied with the age of osteotomy union. The study found that all bones sustained spiral fractures through the osteotomy site. The maximum torque capacity and stiffness increased with age of union. There is an apparent biphasic pattern in the remodelling process. Up till the 13th week there was a decline in the polar moment of inertia and a rise in the torsional stress with an increase in strength. We postulate that this was due to a reduction of the outer diameter of the external bridging callus. After the 13th week, there was a reversal in the process and the outer diameter of the callus increased. The findings provide a baseline reference for future studies involving osteotomy healing as is necessary in bone allograft reconstruction and bone transport.