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Biomedical subjects

K C Aune

Publications and source records attributed to K C Aune.

At least 19 recordsLinked to original sources

Computer databases of medical school curricula.

As the pace of curriculum reform in medical education has accelerated during the past decade, so too have demands on curriculum managers to supply increasingly detailed information about the curriculum. In response, a number of schools have joined together to begin work on designs for computer databases of the curriculum. The authors describe three of the most mature curriculum database prototypes, developed by groups at the medical schools of the University of North Carolina at Chapel Hill (UNC), The University of Maryland, and the University of Miami. All three groups have employed relational database management systems to organize information about each "instructional unit" in the preclinical curriculum, including a set of keywords defining the major concepts presented. The keywords are indexed to a controlled vocabulary, either the Medical Subject Headings (MeSH) or a MeSH derivative. The UNC database also employs a textfile management system to provide users with an overview of the entire curriculum. Future work will focus on identifying a suitable controlled vocabulary; capturing content in greater contextual detail; incorporating alternative learning formats, such as problem-based learning; creating links between content items and examination questions; and capturing information generated by student-patient interactions in clinical settings. As a result of recent collaboration with the Association of American Medical Colleges, work to define a prototype national database has begun and a consortium of interested schools is addressing further development activities.

Abstracting and Indexing↗

Assessment by sedimentation equilibrium analysis of a heterologous macromolecular interaction in the presence of self-association: interaction of S5 with S8.

The proteins S5 and S8 from the Escherichia coli 30S ribosomal subunit have been examined by sedimentation equilibrium methods for behavior in solution as isolated components and in mixtures. The means of resolving two simultaneous associations in this system is discussed, and the energy of association of S5 and S8 is reported. It was found that protein S5 from the MRE 600 strain tends to self-associate weakly at 4 degree C in a manner that can be described as an isodesmic self-association with an association constant and corresponding standard Gibbs free energy equal to (7.7 +/- 0.7) X 10(3) M-1 and -4.9 +/- 0.1 kcal/mol, respectively. Protein S8 was found to have a molecular weight of 15800 and was monomeric in a pure state. Mixtures of S5 and S8 clearly demonstrated the presence of an S5-S8 complex in addition to the self-association of S5. The equilibrium constant of association for the formation of a simple S5-S8 complex at 4 degree C and the corresponding standard Gibbs free energy were found to be (5.5 +/- 1.0) X 10(4) M-1 and -6.0 +/- 0.1 kcal/mol, respectively.

Escherichia coli↗

Solution behavior of proteins L7/L12 from the 50S ribosomal subunit of Escherichia coli.

The behavior of Escherichia coli 50S ribosomal subunit proteins L7/L12 has been investigated in ribosome reconstitution buffer, TMK buffer, by sedimentation equilibrium and analytical gel filtration. Contrary to previous reports that L7/L12 exists in solution solely as dimer species [Möller, W., Groene, A., Terhorst, C., & Amons, R. (1972) Eur J. Biochem. 25, 5], results presented here indicate that L7/L12 undergoes a monomer-dimer-tetramer self-association, with equal equilibrium constants of 3.5 x 10(4) M-1 obtained for the monomer-dimer and dimer-tetramer steps. These results yield standard Gibbs' free energies of -6.1 +/ 0.6 kcal/mol at 20 degrees C. The observed absence of temperature dependence of this interaction over the range 5-25 degrees C indicated a zero standard enthalpy of self-association. Gel filtration results are presented that confirm the highly elongated shape of the L7/L12 molecule. The data suggest the corresponding Stokes radii for the monomer, dimer, and tetramer are 21-23, 26-28, and 29-32 omicron A, respectively. The significance of these results is discussed.

Amino Acids↗

Characterization of reticulocyte release factor.

The release factor (RF) of reticulocytes has been purified to greater than 75% homogeneity. The RF has a native molecular weight of 105,000 and subunit molecular weight of 56,500. The RF protein will bind to reticulocyte ribosomes in response to UAAA, UAGA, or UGAA and therefore participates in codon recognition. The fraction possess a ribosome-dependent GTPase activity. The RF is stimulated in its activity by a second protein fraction.

Animals↗

Physical properties of the dimyristoylphosphatidylcholine vesicle and of complexes formed by its interaction with apolipoprotein C-III.

The structure of a single bilayer vesicle of dimyristoylphosphatidylcholine has been characterized by sedimentation, densimetry, and light-scattering measurements. The molecular weight, partial specific volume, Stokes radius, and degree by hydration were found to be 2.68 X 10(6), 0.972 cm3/g, 125 A, and 0.86 g/g, respectively. From these quantities, a spherically symmetrical model has been derived that features a phospholipid bilayer 35.5 A thick and a hydration shell 9.3 A thick. This particle was shown to bind apolipoprotein C-III (apoC-III) up to 0.08 g/g without loss of its original vesicular structure. At protein-lipid ratios in excess of 0.08 g/g, sedimentation, gel chromatography, and light-scattering measurement indicated a dramatic decrease in Stokes radius and molecular weight. The sedimentation data showed these parameters to become constant at protein-lipid ratios in excess of 0.25 g/g. In this region, the Stokes radius and molecular weight were found to be approximately 80 A and 442 000, respectively. Within the constraints of these values and other data, several models for this complex are discussed.

Apolipoproteins↗

Investigation of the aggregation and activation of prothrombin using quasi-elastic light scattering.

The technique of quasi-elastic light scattering was used to measure the translational diffusion coefficient, D, of purified human prothrombin in buffered aqueous solutions and to monitor for the first time the fragmentation of this protein as it is converted to thrombin. The values of D20,w, measured at two different concentrations, are 4.72 X 10(-7) CM2/S at 2MG/CM3 and 4.51 X 10(-7) CM2/S at 5MG/CM3; the corresponding molecular weights (Mw of 92 000 and 120 000), obtained by combining sedimentation velocity measurements with the diffusion data, confirm the presence of molecular aggregates of prothrombin in these solutions. These results, as well as analysis of the intensity-intensity autocorrelation functions from two-component systems with various dimer conformations, indicated the presence of end-to-end dimers in these prothrombin solutions. The values obtained for D indicate a dimer weight fraction of 0.4 to 0.5 in the 2 mg/cm3 solution and 0.6 or greater in the 5 mg/cm3 solution. The fragmentation of prothrombin was monitored in a nonphysiologic activation system, containing taipan snake venom, dihexanoylphosphatidylcholine, and CaCl2. At a temperature of 15 degrees C, conversion to thrombin proceeded very slowly and was still incomplete after 90 h. A method for determing the percentage of converted prothrombin is an activated system containing aggregates from the average value of D and light scattering data is discussed.

Chemical Phenomena↗

Isolation, chemical characterization, and biophysical properties of three different abnormal lipoproteins: LP-X1, LP-X2, and LP-X3.

Three different but related abnormal lipoprotein species, LP-X1, LP-X2, and LP-X3, have been isolated from cholestatic plasma by ethanol precipitation and zonal ultracentrifugation. All three populations are rich in phospholipids (64.9 to 67.5%) and cholesterol (23.0 to 26.8%) but poor in cholesteryl esters (0.4 to 1.9%), triglycerides (1.8 to 3.2%), and protein (3.2 to 6.7%) with differences in chemical composition which result in buoyant densities (1.038, 1.049, and 1.058, respectively) to allow their separation. LP-X1, LP-X2, and LP-X3 exhibited apparent flotation rates of 17.3, 9.7, and 3.2 Svedbergs and Stokes radii of 339, 343, and 294 A, respectively. As determined from circular dichroic measurements, the protein constituents of all three particles possessed a high degree of alpha helical structure (41 to 65%). Each LP-X particle exhibited abnormally low fluidity as evaluated by electron paramagnetic resonance. All of the particles contained human serum albumin and the C-proteins as major protein constituents, but only LP-X2 and LP-X3 contained apolipoprotein A-I and apolipoprotein E.

Apolipoproteins↗

Molecular interactions between ribosomal proteins. Evidence for specificity of interaction between isolated proteins.

The proteins S2, S3, S5, and S10 from the 30S ribosomal subunit of Escherichia coli was studied by analytical ultracentrifugation to characterize them in solution and to determine whether isolated protein-protein interactions exist. Such interactions, if specific, may therefore bear some relationship to the spatial organization of the subunit structure. It was found that protein S2 self-associates to a slight extent and that solution mixtures of S2 and S3 contain only enough dimeric species to account for the S2 dimer. Hence, no observable interaction was detected between S2 and S3. Solution mixtures of proteins S5 and S10 revealed a species of molecular weight greater than either protein. The proposal is that S5 and S10 interact with an association equilibrium constant of 7.6 X 10(-5) M-1 at 3 degrees in a Tris buffer at pH 7.4. It was also shown that solution with a 1:1:1 mixture by mass, of S2, S5, and S10 contained a species possessing a molecular weight consistent with a simple ternary complex of the three proteins.

Bacterial Proteins↗

Physical properties of some ribosomal proteins in solution and evidence for molecular interactions between isolated ribosomal proteins.

Many previous studies have been directed toward obtaining a physical visualization of the relationship between the protein and RNA in the ribosomal subunits isolated from Escherichia coli. The current study is the first report where an attempt has been made to directly assess interactions between a pair of isolated ribosomal proteins separate from the intact system by means of sedimentation equilibrium analysis. The molecular weights of the proteins S3, S4, S5, S6, S7, S8, and S20 from the 30S subunit of the E. coli ribosome were determined under conditions of assembly of the subunit by sedimentation equilibrium. All of the proteins exhibited molecular weights consistent with monomeric behavior (i.e., in agreement with the measurement of the ultimate molecular weight in denaturing solvents as reported in other studies as well as in the current study) except S8 which indicates a tendency to self-associate. Hydrodynamic measurements on the proteins indicate that these proteins are not completely disorganized in solution such as a random coil, although not as compact as globular proteins. The frictional coefficient ratios found for these ribosomal proteins range from 1.4 to 1.9. The hydrodynamic data are discussed as containing some evidence that stable interaction sites could exist in the proteins. The molecular weight data are considered pertinent to a sedimentation equilibrium study of protein-protein interactions that may be occurring in the ribosomal subunits. Two proteins, S3 and S5, considered in this investigation were found to exhibit no tendency to self-associate under conditions of reassembly. When the two proteins are mixed under those same conditions, however, a species with a molecular weight greater than that of either S3 or S5 is observed to be formed. The interpretation is presented that a molecular interaction between S3 and S5 is the cause. The system is described as containing S3, S5, and a complex between S3 and S5 with a stoichiometry of 1:1 and an association equilibrium constant of 5.7 times 10-5 l./mol (delta G-o equals minus 7.25 kcal/mol). Since the association appears to be specific and of moderate strength, it is concluded that the interaction could have some pertinence with respect to conferring a structural arrangement in the ribosomal subunit. Moreover, it is concluded that protein-protein interactions, in general, must be considered in addition to the well documented significant RNA-protein relationships when models for ribosome structure and assembly are formulated.

Amino Acids↗