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Abstract:This article discusses methodological strengths and limitations of federally managed postsecondary data with American Indian/Alaska Native (AI/AN) college student populations. To support understanding, we define fundamental research and measurement validity concepts associated with credible quantitative research. The validity concepts are then applied to dominant culture and AI/AN postsecondary persistence theories. Challenges of conducting scientifically valid research with AI/AN populations using large federally available datasets are considered within the described research and measurement validity frameworks. Our critique focuses on vital needs for culturally relevant constructs and AI/AN subpopulation-specific studies. Our discussion concludes with implications and policy recommendations for postsecondary research with AIs/ANs.

The interaction of dynamin II with giant unilamellar vesicles was studied using two-photon fluorescence microscopy. Dynamin II, labeled with fluorescein, was injected into a microscope chamber containing giant unilamellar vesicles, which were composed of either pure 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or a mixture of POPC and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). Binding of the fluorescent dynamin II to giant unilamellar vesicles, in the presence and absence of PI(4,5)P2, was directly observed using two-photon fluorescence microscopy. This binding was also visualized using the fluorescent N-methylanthraniloyl guanosine 5′-[γ-thio]triphosphate analogue. The membrane probe 6-dodecanoyl-2-dimethylamine-naphthalene was used to monitor the physical state of the lipid in the giant unilamellar vesicles in the absence and presence of dynamin. A surprising finding was the fact that dynamin II bound to vesicles in the absence of PI(4,5)P2. Activation of the GTPase activity of dynamin II by pure POPC was then shown.

In this report the temperature dependence of photoinduced electron transfer between both singlet- and triplet-state uroporphyrin (¹URO and ³URO, respectively) and the heme group of ferricytochrome c (Cc) has been examined. Analysis of the forward electron-transfer rate originating from ¹URO as a function of temperature gives a reorganizational energy (λ) of 1.0 ± 0.02 eV with an associated electronic coupling term (HAB) of (3.7 ± 0.3) × 10^-4 eV. In addition, the singlet lifetime data exhibit a temperature-dependent Gaussian distribution that narrows as the temperature increases. This suggests a conformational distribution of bound porphyrin with a narrow range of potential wells at lower temperatures. The corresponding temperature dependence of the electron transfer between ³URO/URO⁺ and the heme group of Cc gives a λ = 0.49 ± 0.05 eV/0.19 ± 0.03 eV and HAB ~ 4 × 10^-4 eV/1.4 × 10^-4 eV, respectively. These observations are consistent with orientational dependent conformational states as well as possible gating of electron transfer within the complex.

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Hydrolysis of GTP by dynamin is essential for budding clathrin-coated vesicles from the plasma membrane. Two distinct domains of dynamin are implicated in the interactions with dynamin GTPase activators. Microtubules and Grb2 bind to the carboxyl-terminal proline/arginine-rich domain (PRD), whereas phosphoinositides bind to the pleckstrin homology (PH) domain. In this study we tested the effect of different phosphoinositides on dynamin GTPase activity and found that the best activator is phosphatidylinositol 4,5-bisphosphate followed by 1-O-(1, 2-di-O-palmitoyl-sn-glycerol-3-benzyloxyphosphoryl)-D-myo-inositol 3,4,5-triphosphate. Phosphatidylinositol 4-phosphate was a weak activator and phosphatidylinositol 3,4-bisphosphate did not activate GTPase at all. We then addressed the question of whether both domains of dynamin, PRD and PH, can be engaged simultaneously, and determined the effects of dual occupancy on dynamin GTPase activity. We found that Grb2 and phosphatidylinositol 4,5-bisphosphate together increased the dynamin GTPase activity up to 4-fold higher than that obtained by these activators tested separately, and also reduced the dynamin concentration required for half-maximal activities by 3-fold. These results indicate that both stimulators can bind to dynamin simultaneously resulting in superactivation of dynamin GTPase activity. We propose that SH3-containing proteins such as Grb2 bind to the dynamin PRD to target it to clathrin-coated pits and prime it for superactivation by phosphoinositides.

The INSURRECT project uses the SuperJANET network to link six sites in the UK for interactive teaching and learning in surgery, an area of higher education where visual information is critical to the learning process. Collaboration between the six universities allows students access to a larger pool of surgical expertise and case studies than any single institution could provide. The project expects to improve the time that medical students can devote to surgery by up to 50%, by providing both supervised and unsupervised access to important visual information and case studies. Finally, the reduction in student numbers in operating theatres should reduce the infection risk to patients. A key component of the project is the central image resource, located in London, but allowing students and surgeons access from anywhere on the network. This paper describes the development of the interactive surgical teaching system and our experience with it during the first 18 months. One subjective observation, noticed after just one term's teaching, was the improved quality of the teaching.

The familial dysalbuminemic hyperthyroxinemia (FDH) phenotype results from a natural human serum albumin (HSA) mutant with histidine instead of arginine at amino acid position 218. This mutation results in an enhanced affinity for thyroxine. Site-directed mutagenesis and a yeast protein expression system were used to synthesize wild type HSA and FDH HSA as well as several other HSA mutants. Studies on the binding of thyroxine to these HSA species using equilibrium dialysis and quenching of tryptophan 214 fluorescence suggest that the FDH mutation affects a single thyroxine binding site located in the 2A subdomain of HSA. Site-directed mutagenesis of HSA and thyroxine analogs were used to obtain information about the mechanism of thyroxine binding to both wild type and FDH HSA. These studies suggest that the guanidino group of arginine at amino acid position 218 in wild type HSA is involved in an unfavorable binding interaction with the amino group of thyroxine, whereas histidine at amino acid position 218 in FDH HSA is involved in a favorable binding interaction with thyroxine. Neither arginine at amino acid position 222 nor tryptophan at amino acid position 214 appears to favorably influence the binding of thyroxine to wild type HSA.

A computer system has been developed to assist in preparing data for interstitial and intracavitary calculations.This approach uses graphic and interactive techniques, and removes all the format problems which lead to errors in data preparation. The program reconstructs the implant and rotates it about X, Y and Z axes to allow close examination of the positions of the radiation sources.The site of the dose calculation can be selected by positioning a frame representing the calculation plane in the reconstructed implant. The output of the program is the three-dimensional data of the source and plane co-ordinates, together with the co-ordinates to define the area on the plane where the calculation is to be performed.

A system is described which incorporates the use of a diagnostic and treatment advice expert system into the routine information-handling functions of a surgical breast clinic. The main focus of the system is on identification and management of non-malignant breast disease. The advisor is linked with a clinical database which is used to hold summary case notes, and from which reports forming the basis for audit of case-mix and resource utilization can be produced. The system uses backward chaining of extended production rules and a relational database, and runs on a desktop microcomputer.

Diuretic resistance to furosemide in the nephrotic syndrome (NS) may result from binding of drug to filtered albumin within the renal tubule. In buffer solutions intended to partially mimic the luminal environment of the distal nephron during the NS, we examined several chemical properties to determine their effect on furosemide-albumin binding equilibria. Dissociation constants were obtained by measuring furosemide's quenching of human serum albumin's intrinsic tryptophan fluorescence over ranges of pH, ionic strength (IS) and osmolarity. Neither pH nor osmolarity significantly affected binding; however, incremental increases in IS between 0.0 and 1.0 produced increases in Kd from 0.65 +/- 0.05 to 34.38 +/- 1.72 microM, resulting in a 5- and 28-fold increase in the unbound furosemide fraction when the furosemide-albumin concentrations were 3.0:5.0 and 10.0:45.0 microM, respectively. Our results indicate that human serum albumin contains one high affinity binding site for furosemide that is sensitive to IS. Because of changes in the concentrations of reactants as well as IS that can occur in nephron segments distal to furosemide's site of action, we conclude that the amount of unbound (i.e., pharmacologically active) drug in voided urine will not necessarily correspond to the amount at the active site. To clinically assess the pharmacodynamic consequence of protein binding in the NS, changes in the concentration of the reactants and IS in the distal nephron must be minimized so that the unbound furosemide measured in voided urine will accurately reflect the amount at the drug's active site.

Summary Radiation action occurs over a broad timescale which extends from the very early physical processes associated with energy absorption to the very late biological effects, such as carcinogenesis which may not become apparent until many years later. The various temporal stages of radiation action are classified and their interrelationships described. Experimental projects in cellular radiation chemistry, including pulse radiolysis, are discussed, together with some applications of the techniques in this general area.

The present study examines photoinduced electron transfer within self-assembled complexes between cytochrome c and either free base uroporphyrin (URO) or free base tetrakis(4-carboxyphenyl)porphyrin (4CP). In both systems, complexation of the porphyrin to the protein results in bathochromic shifts in the absorption bands of the porphyrin. Interestingly, equilibrium circular dichroism data demonstrate significant differences in the orientation of the bound porphyrins. The effect of orientational differences on photoinduced electron transfer between the bound porphyrin and the heme group of cytochrome c are demonstrated in the steady-state and time-resolved fluorescence and triplet−triplet transient absorption data obtained for the two complexes. In the case of the cytochrome c&sbd;4CP complex, the singlet state of the 4CP is significantly quenched by the heme group of the protein. Analysis of the time-resolved fluorescence data reveals two discrete lifetime components at 9.3 (free 4CP) and 1.27 ns (bound 4CP). In contrast, the singlet state of URO is only moderately quenched by complexation to the protein. Fluorescence lifetime analysis reveals two components consisting of a discrete component at 15.7 ns (free URO) and a Lorentzian distribution of lifetimes centered at 3.8 ns. However, URO exhibits significant triplet-state quenching, resulting in intercomplex electron transfer in which the observed forward and reverse rates are similar ((1.8 ± 0.2) × 10⁶ and (1.6 ± 0.4) × 10⁶ s^-1, respectively). The difference in ET mechanism (i.e., singlet versus triplet) can be rationalized in terms of distinct dipole orientations of the bound porphyrins relative to the heme group of the protein. We further speculate that the orientational differences between bound URO and bound 4CP arise due to the flexibility of the URO side chains.

The singlet excited state behavior of tetrakis(4-N-methylpyridyl)porphine (T4MPyP) in the presence of the four mononucleotides of DNA in aqueous solution has been examined. Addition of the nucleotides of adenine, thymine, or cytosine to a solution containing T4MPyP results in an increase in the fluorescence intensity of the porphyrin, while addition of guanine substantially quenches the intensity. Optical absorption measurements demonstrate noncovalent interactions of the nucleotides with the porphyrin, resulting in bathochromic shifts in the Soret region. Binding constants for the base:porphyrin complexes were determined from steady-state absorption data to be 1743 ± 68, 385 ± 15, 2433 ± 150, and 198 ± 7 M^-1 for dAMP, dTMP, dGMP, and dCMP, respectively. The T4MPyP singlet state lifetime increases from 5.29 to 11.3, 10.3, and 7.8 ns in the presence of dAMP, dTMP, and dCMP, respectively. In the case of dGMP, the lifetime data was best fit to a Lorentzian distribution centered at 0.69 ns and a discrete component at 3 ns. The quenching was modeled using an excited state reaction mechanism coupled with ground state complexation. The quenching is attributed to electron transfer between guanine (the most reducing of the bases) and T4MPyP (i.e., reductive quenching of the porphyrin singlet state).

To investigate the mechanisms by which hydrostatic pressure inhibits (Na,K)-ATPase, we measured enzyme activity, as a function of pressure and temperature, of purified (Na,K)-ATPase from dog kidney and eel electroplax, and we monitored protein conformation, possible subunit interactions, and the fluidity of the membrane with fluorescent probes. The (Na,K)-ATPase and p-nitrophenylphosphatase activities were inhibited reversibly by pressures below 1.5 kilobars (eel enzyme) and 2.5 kilobars (dog kidney enzyme). Above these pressures, the enzymes were inactivated irreversibly. The plots of 1n(activity) versus pressure were curvilinear; this indicates that the reversible inhibition by pressure involves two or more rate-limiting steps. The calculated activation volumes varied with temperature and pressure and were larger for the (Na,K)-ATPase activity compared to the p-nitrophenylphosphatase activity. The fluorescence polarization of three hydrophobic probes decreased with increasing temperature (10-36 degrees C) and increased with increasing pressure (10(-3)-1.5 kilobars), reversibly, without any evidence of a lipid phase transition. Plots of enzyme activity versus fluorescence polarization of the lipid probes showed an inverse relationship; this indicates that enzyme activity was directly related to the fluidity of the membrane as measured by the lipid probes. Pressure had no effect on the fluorescence polarization of two cardiac glycoside probes nor on the efficiency of resonance energy transfer between either donor and acceptor cardiac glycosides specifically bound to the ouabain sites of different alpha-subunits, or tryptophan and the bound cardiac glycoside probe. These results suggest that dissociation of dimeric alpha-subunits is not related to the inhibition by pressure, and that the cardiac glycoside-complexed enzyme conformation is stabilized by pressure. It is concluded that increased pressure decreases the membrane fluidity which hinders conformational transitions associated with rate-limiting steps of the (Na,K)-ATPase reaction. It is proposed that ion-bound or -occluded forms of (Na,K)-ATPase are stabilized by pressure because they occupy a smaller volume.

The fluorescent probe tetramethylrhodamine iodoacetamide was attached to cysteine residues substituted at various specific locations in full-length and deletion variants of the homodimeric Escherichia coli ribosomal protein L7/L12. Ground-state tetramethylrhodamine dimers form between the two subunits of L7/L12 depending upon the location of the probe. The formation of tetramethylrhodamine dimers caused the appearance of a new absorption band at 518 nm that was used to estimate the extent of interaction of the probes in the different protein variants. Intersubunit tetramethylrhodamine dimers form when tetramethylrhodamine acetamide is attached to two different sites in the N-terminal domain of the L7/L12 dimer (residues 12 or 33), but not when attached to sites in the C-terminal domain (residues 63, 89, or 99). The tetramethylrhodamine dimers do form at sites in the C-terminal domain in L7/L12 variants that contain deletions of 11 or 18 residues within the putative flexible hinge that separates the N- and C-terminal domains. The tetramethylrhodamine dimers disappear rapidly (within 5 s) upon addition of excess unlabeled wild-type L7/L12. It appears that singly labeled L7/L12 dimers are formed by exchange with wild-type dimers. Binding of L7/L12:tetramethylrhodamine cysteine 33 or cysteine 12 dimers either to L7/L12-depleted ribosomal core particles, or to ribosomal protein L10 alone, results in disappearance of the 518-nm absorption band. This result implies a conformational change in the N-terminal domain of L7/L12 upon its binding to the ribosome, or to L10.

The time course of recovery from chromatic adaptation in human vision was tracked by determining the wavelength of light that appears uniquely yellow (neither red nor green) both before and after exposure to yellowish green and yellowish red adapting lights. Recovery is complete within 5 min after steady light exposure. After exposure to the alternating repeated sequence 10-sec light/10-sec dark, the initial magnitude of the aftereffect is reduced but recovery is retarded. The results are interpreted in terms of two processes located at different levels in the hierarchical organization of the visual system. One is a change in the balance of cone receptor sensitivities; the second is a shift in the equilibrium baseline between opposite-signed responses of the red/green channel at the opponent-process neural level. The baseline-shift mechanism is effective in the condition in which repeated input signals originating at the receptors are of sufficient strength to activate the system effectively. Hence, this process is revealed in the alternating adaptation condition when the receptors undergo partial recovery after each light exposure, but receptor adaptation during continued steady light exposure effectively protects the subsequent neural systems from continued strong activation.

A programmed graphics terminal has been connected on-line to a large time-shared computer for calculating dose distributions in radiotherapy treatment planning and provides a viable alternative to dedicated systems and batch working. The terminal equipment is based on a minicomputer and includes a function-key device for outline input, a large-screen refresh oscilloscope for viewing results and an X-Y plotter for hard-copy. Radiotherapy dose computation programs in standard Fortran are stored and run on a large remote computer with graphical interaction at the terminal. External beam programs can calculate dose distributions for most commonly used treatment situations and can compute in off-axis planes. Data input is fully interactive and easy to understand. Dose distributions are displayed as isodose contours. Advantages of the system include accuracy, speed, ease of use and maintenance, and transferability of the programs between different host computers.The advantages to be gained by the use of digital computers for calculation of dose distributions in radiotherapy treatment planning are now well accepted by those working in the field, and efforts in this direction have resulted in a multiplicity of approaches in both the nature of the programs for the computations and in the equipment on which the programs are implemented. Wood (1974) gives a useful survey of the field.

A computer program was written to determine how to deliver the external supplementary beam dose to patients who have been treated with intracavitary radium for gynaecological conditions. A double wedge filter is used at three source-skin distances and can be moved to five positions relative to the centre of the radiation beam. This gives 15 dose distributions, and the program determines which distributions to use and the dose to be delivered by each distribution.

A system using an Elliott 803 computer with magnetic film backing store was designed to perform calculations in three dimensions in intracavitary and interstitial radiation dosimetry. This system was developed from the experience gained in using another program for three years. The system is in modular form; each individual program performs a different stage of the calculation. These programs are stored on the magnetic film and are so arranged that they can be altered or replaced without having to rewrite the whole system. Programs are included to carry out calculations for point sources, line sources and linear filtered sources. The system has been designed either to carry out simple routine calculations or to incorporate various correction factors. The system also provides facilities to plan the supplementary external beam treatment for patients who have already had intracavitary treatment.

A new family of planar tridentate ligands (III) and (IV), which are structural analogues to terpyridine with the added feature that the ligand superstructure can be conveniently varied, are prepared according to the scheme.

Solvent dipolar reorientations following excitation of DANCA (I) in glycerol at various temp. are investigated using multifrequency‐phase fluorometry.

Preparation of the tridentate ligand compounds (Va), (Vb), and (X) is described.

In the Mount Vernon method for calculating dose distributions in circumaxial arc therapy (Jones, Gregory and Birchall, 1956) an arc treatment of, say, 220 deg. is regarded as equivalent to the sum of the individual contributions from the appropriate fixed-field isodose chart when placed successively on 12 radii, each separated by 20 deg., the first and twelfth radii being at the ends of the arc. Practical measurements made in a phantom with our “Theratron B” unit appeared to support this assumption.