Re-evaluation of the corrected signal from fluoroscopic probe measurements.
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Fluorescent Dyes↗
Biomedical subjects
J I Kaplan
Publications and source records attributed to J I Kaplan.
Analysis of 31P NMR spectra of enzyme-bound reactants and products of adenylate kinase using density matrix theory of chemical exchange.
31P NMR spectra of equilibrium mixtures of enzyme-bound reactants and products of the adenylate kinase reaction (formula; see text) were analyzed by using computer simulations based on density matrix theory of chemical exchange. Since adenylate kinase has the unique feature that the reactants in the reverse direction are both ADP molecules, which are indistinguishable off the enzyme, the density matrix equations are formulated for the ABC + D in equilibrium A'B' + A"B" exchange appropriate for the reaction, in which the interchange of A'B' and A"B" is explicitly introduced. It is shown that the consideration of this interchange is essential to explain the experimentally observed line shapes. By comparison of the computer-simulated spectra with various values for the rates of the exchange with the experimental spectra for porcine adenylate kinase at pH 7.0 and T = 4 degrees C, the following characteristic rates were determined: interconversion rates, 375 +/- 30 s-1 (ATP formation) and 600 +/- 50 s-1 (ADP formation); interchange rates of donor and acceptor ADP's, 100 +/- 30 s-1 (in the presence of optimal Mg2+ concentration), 1500 +/- 100 s-1 (in the absence of Mg2+). It is shown that under the conditions of the experiments the interchange rate is the lower limit of the dissociation rate of ADP (or MgADP from the acceptor site if Mg2+ was present) from the enzyme complexes. The significance of these interchange rates and their values relative to the interconversion rates is discussed with special reference to the role of the Mg2+ ion in the differentiation of the two nucleotide binding sites on adenylate kinase.
Adenylate Kinase↗
Magnetic x-ray collimator (MXC).
The magnetic x-ray collimator ( MXC ) is proposed as a replacement for the standard x-ray cylinder with a visual display permitting operator alignment and collimation of the beam to approximately the size of the film, thereby allowing a 67% reduction in the area of the patient's face that is irradiated.
Cost-Benefit Analysis↗
Prolongation of proton spin lattice relaxation times in regionally ischemic tissue from dog hearts.
Proton NMR techniques were used to characterize acutely ischemic myocardial tissue from the dog. Ligation of the left anterior descending coronary artery for 30 min resulted in a consistent prolongation of the proton spin-lattice relaxation times (T1) in samples from regionally ischemic heart muscle when compared with T1 values for nonischemic areas from the same hearts. The relative prolongation of relaxation times in ischemic tissue was found to increase as the duration of ischemia was extended to 60 or 120 min. T1 values for ischemic tissue were not directly related to tissue levels of high-energy compounds, lactate, or hydrogen ions but largely reflected the increased water content of the regionally ischemic myocardium. Proton NMR analysis provides a means of identifying acute regional ischemia in heart tissue, and in the future may permit three-dimensional imaging of the heart in vivo.
Animals↗
Theoretical shapes of bilipid vesicles under conditions of increasing membrane area.
Certain standard properties, including spontaneous curvature, are assumed for the membrane of a bilipid vesicle. Then, if there is a mechanism that causes the membrane area to increase, vesicle cleavage is found to occur.
Lipid Bilayers↗