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An improved multi-purpose teaching attachment.
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The role of Arg46 and Arg47 of antithrombin in heparin binding.
Heparin greatly accelerates the reaction between antithrombin and its target proteinases, thrombin and factor Xa, by virtue of a specific pentasaccharide sequence of heparin binding to antithrombin. The binding occurs in two steps, an initial weak interaction inducing a conformational change of antithrombin that increases the affinity for heparin and activates the inhibitor. Arg46 and Arg47 of antithrombin have been implicated in heparin binding by studies of natural and recombinant variants and by the crystal structure of a pentasaccharide-antithrombin complex. We have mutated these two residues to Ala or His to determine their role in the heparin-binding mechanism. The dissociation constants for the binding of both full-length heparin and pentasaccharide to the R46A and R47H variants were increased 3-4-fold and 20-30-fold, respectively, at pH 7.4. Arg46 thus contributes only little to the binding, whereas Arg47 is of appreciable importance. The ionic strength dependence of the dissociation constant for pentasaccharide binding to the R47H variant showed that the decrease in affinity was due to the loss of both one charge interaction and nonionic interactions. Rapid-kinetics studies further revealed that the affinity loss was caused by both a somewhat lower forward rate constant and a greater reverse rate constant of the conformational change step, while the affinity of the initial binding step was unaffected. Arg47 is thus not involved in the initial weak binding of heparin to antithrombin but is important for the heparin-induced conformational change. These results are in agreement with a previously proposed model, in which an initial low-affinity binding of the nonreducing-end trisaccharide of the heparin pentasaccharide induces the antithrombin conformational change. This change positions Arg47 and other residues for optimal interaction with the reducing-end disaccharide, thereby locking the inhibitor in the activated state.
Building nursing within the American Heart Association.
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Organ donation in three major American cities with large Latino and black populations.
It has been suggested that areas with large inner-city Black and Latino populations have worse organ donation rates than those with large suburban and rural White populations. Yet data are sparse. We studied family refusal rates (FRRs) to cadaver organ donation between 1/84 and 5/87 in three United States city-areas (New York, Los Angeles, and Miami) with large Black and distinct Latino populations. Blacks are at least 18% and Latinos at least 25% of the combined general population of the three cities, totaling over three and four million people, respectively. In addition, Blacks and Latinos represent 42% of cadaver transplant recipients, 49% of patients on waiting lists, and 57% of the patients on dialysis in the three cities. Combining the data from the three cities, Black (45%) and Latino (43%) FRRs were similar (P = .78), and each was significantly higher than that in the White population (17%) (P less than 0.0001). The overall refusal rate in NYC (42%) was significantly higher (P less than .0001) than in LA (26%) or Miami (21%), and LA's refusal rate was significantly higher than Miami (P = .03). The refusal rates for the White (31%) and Black (55%) populations in NYC were each significantly higher than their respective populations in LA (14% and 33%) or Miami (11% and 36%) (P less than .05). Although Miami Latinos had a lower FRR (35%) than Latinos in NYC (46%) or LA (45%), the difference was not statistically significant (P = .19 and P = .20, respectively). In the three cities combined, 515 of a possible 1772 medically and legally eligible organ donors were lost during the 40 months studied due to families' refusal of consent. This represents approximately 1000 transplantable kidneys and large numbers of extrarenal organs. Further studies are needed to elucidate the reasons for differences in donation rate among groups and regions in the United States.
1992 Genetics Society of America Medal: Maynard V. Olson.
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Age-related effects in rabbit hearts of N6-R-phenylisopropyladenosine, an adenosine A1 receptor agonist.
Interventions known to increase cytoplasmic Ca2+ appear to amplify age-related impairment of cardiac function. In addition, increased release of interstitial adenosine, an endogenous nucleoside, has been suggested to mediate the diminished beta-adrenergic responsiveness in senescent heart. However, the direct effects of adenosine A1 receptor activation on senescent myocardium have not been investigated thoroughly. Therefore, the effects of N6-R-phenylisopropyladenosine (R-PIA), an A1 agonist, on atrial rate and contractility (+dF/dt) in adult (6-8 months) and senescent (5-7 years) New Zealand White rabbits were compared in spontaneously beating right atria and electrically stimulated isolated right papillary muscles. Although senescent right atria appeared to be more sensitive to the negative chronotropic-effects of R-PIA, the effective concentrations producing 50% of the maximum response (EC50 values) of R-PIA were not significantly different between adult (26 nM, 95% confidence limits: 12-52 nM) and senescent (13 nM; 95% confidence limits: 10-16 nM). However, senescent right ventricular papillary muscles were more sensitive to the negative inotropic effects of R-PIA. For example, at 90 contractions/min, 100 nM R-PIA decreased +dF/dt 25.3 +/- 7.4% and 61.9 +/- 4.8% in adult and senescent papillary muscles, respectively. To investigate whether R-PIA might alter sarcoplasmic reticulum (SR) function as a mechanism of decreased inotropy, we determined the inotropic effects of R-PIA on steady-state and 30-s postrest-potentiated contractions (PRP; an index of SR Ca2+ release) of left atria. R-PIA did not selectively decrease contractility of PRP compared to steady state in either adult or senescent left atria.(ABSTRACT TRUNCATED AT 250 WORDS)
Nonpension retiree benefits: are they for life? Management guidelines to the issue.
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Summary report of a study of academic medical library statistics.
Common statistical analyses were applied to the statistics on medical school libraries published in 1964 and 1966 in the Bulletin to assess the potential utility of such survey data. The major conclusions of the study are that these statistics (1) are highly redundant; (2) are essentially descriptive and not amenable to analysis for predictive purposes; (3) are of questionable reliability; (4) are of minimal utility for library investigators and managers, and of doubtful value for establishing standards. The authors believe that, rather than continuing to collect similar statistics in the future, we need a systematic program to define specific requirements of data use and to design survey methods that will produce data meeting these requirements.
Lysine 114 of antithrombin is of crucial importance for the affinity and kinetics of heparin pentasaccharide binding.
Lys(114) of the plasma coagulation proteinase inhibitor, antithrombin, has been implicated in binding of the glycosaminoglycan activator, heparin, by previous mutagenesis studies and by the crystal structure of antithrombin in complex with the active pentasaccharide unit of heparin. In the present work, substitution of Lys(114) by Ala or Met was shown to decrease the affinity of antithrombin for heparin and the pentasaccharide by approximately 10(5)-fold at I 0.15, corresponding to a reduction in binding energy of approximately 50%. The decrease in affinity was due to the loss of two to three ionic interactions, consistent with Lys(114) and at least one other basic residue of the inhibitor binding cooperatively to heparin, as well as to substantial nonionic interactions. The mutation minimally affected the initial, weak binding of the two-step mechanism of pentasaccharide binding to antithrombin but appreciably (>40-fold) decreased the forward rate constant of the conformational change in the second step and greatly (>1000-fold) increased the reverse rate constant of this step. Lys(114) is thus of greater importance for the affinity of heparin binding than any of the other antithrombin residues investigated so far, viz. Arg(47), Lys(125), and Arg(129). It contributes more than Arg(47) and Arg(129) to increasing the rate of induction of the activating conformational change, a role presumably exerted by interactions with the nonreducing end trisaccharide unit of the heparin pentasaccharide. However, its major effect, also larger than that of these two residues, is in maintaining antithrombin in the activated state by interactions that most likely involve the reducing end disaccharide unit.
Double Ionization of Helium and Neon for Fast Heavy-Ion Impact: Correlated Motion of Electrons from Bound to Continuum States.
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Quaternary structure of rice nonsymbiotic hemoglobin.
Plant nonsymbiotic hemoglobins are hexacoordinate heme proteins found in all plants. Although expression is linked with hypoxic environmental conditions (Taylor, E. R., Nie, X. Z., Alexander, W. M., and Hill, R. D. (1994) Plant Mol. Biol. 24, 853-862), no discrete physiological function has yet been attributed to this family of proteins. The crystal structure of a nonsymbiotic hemoglobin from rice has recently been determined. The crystalline protein is homodimeric and hexacoordinate with two histidine side chains coordinating the heme iron atom. Despite the fact that the amino acids responsible for the subunit interface are relatively conserved among the nonsymbiotic hemoglobins, previous work suggests that this group of proteins might display variability in quaternary structure (Duff, S. M. G., Wittenberg, J. B., and Hill, R. D. (1997) J. Biol. Chem. 272, 16746-16752; Arredondo-Peter, R., Hargrove, M. S., Sarath, G., Moran, J. F., Lohrman, J., Olson, J. S., and Klucas, R. V. (1997) Plant Physiol. 115, 1259-1266). Analytical ultracentrifugation and size exclusion high pressure liquid chromatography were used to investigate the quaternary structure of rice nonsymbiotic hemoglobin at various states of ligation and oxidation. Additionally, site-directed mutagenesis was used to test the role of several interface amino acids in dimer formation and ligand binding. Results were analyzed in light of possible physiological functions and indicate that the plant nonsymbiotic hemoglobins are not oxygen transport proteins but more closely resemble known oxygen sensors.
The human genome project.
The Human Genome Project in the United States is now well underway. Its programmatic direction was largely set by a National Research Council report issued in 1988. The broad framework supplied by this report has survived almost unchanged despite an upheaval in the technology of genome analysis. This upheaval has primarily affected physical and genetic mapping, the two dominant activities in the present phase of the project. Advances in mapping techniques have allowed good progress toward the specific goals of the project and are also providing strong corollary benefits throughout biomedical research. Actual DNA sequencing of the genomes of the human and model organisms is still at an early stage. There has been little progress in the intrinsic efficiency of DNA-sequence determination. However, refinements in experimental protocols, instrumentation, and project management have made it practical to acquire sequence data on an enlarged scale. It is also increasingly apparent that DNA-sequence data provide a potent means of relating knowledge gained from the study of model organisms to human biology. There is as yet little indication that the infusion of technology from outside biology into the Human Genome Project has been effectively stimulated. Opportunities in this area remain large, posing substantial technical and policy challenges.
Planning the genome institute's future.
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Regional Medical Programs. What are they? Where are they?
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Ancillary service consumption by Military Health Service System special programs: implications for diagnosis related group resource allocation.
An analysis was conducted of consumption of ancillary services by medical treatment facility special programs within the Military Health Service System (MHSS). This workload would not receive explicit credit under the new weighted ambulatory visit/inpatient disposition workload credit system mandated by the National Defense Authorization Act for Fiscal Year 1987. Results indicated that ancillary workload consumption by facility special programs was substantial. When the weighted visit/disposition workload credit system is implemented throughout MHSS, appropriate adjustments must be made to reflect ancillary workload generated by MHSS facilities in support of direct patient care missions but lost under this type of credit system.
Nosocomial infection surveillance, 1984.
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