Biomedical subjects
Publications and source records attributed to L Minkoff.
Proton T1 relaxation times of red blood cells were significantly higher in six bipolar depressed patients than in matched normal control subjects before lithium treatment. Times decreased in five of the six patients following 1 week of lithium therapy.
A technique, field-foxusing nuclear magnetic resonance (n.m.r.) spectroscopy (FONAR), is described for doing n.m.r. scans in large samples. The method utilizes a shaped d.c. magnetic field that confines the n.m.r. signal-producing region of the sample to a small volume called the resonance aperture. The aperture contains the required values of the Ho field to fully bracket the band of the r.f. pulse. The magnet system and r.f. pick-up coil that achieved the first human n.m.r. scan are discussed.
A technique, field-focusing NMR (FONAR), is described for doing NMR scans in large samples. The method utilizes a shaped D.C. magnetic field that confines the NMR-signal-producing region of the sample to a small volume called the resonance aperture. The aperture contains the required values of the Ho field to fully bracket the band of the r.f. pulse. The magnet system and r.f. pick-up coil that achieved the first human NMR can is discussed.
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The 45,000 molecular weight component of an "actin-like" fraction (A-L fraction) from E. coli is identified as actin. Passage of skeletal muscle myosin through the A-L fraction specifically removes the 45,000 molecular weight band visible on electrophoresis prior to passage. Examination of the myosin after passage exhibits a new band on electrophoresis at 45,000 molecular weight.
A giant nitrogen-jacketed liquid-helium metal dewar built in this laboratory is described for housing 53-inch superconducting magnet used in the human FONAR experiments. This dewar is 10 feet tall, 6 feet wide, 18 inches deep, and weighs 1 1/2 tons. It consists of the main magnet hoop connected through a demountable gooseneck to a liquid helium reservoir tank.
The FONAR technique that achieved the first chemical image of the live human being is described. Color and black-and-white video images of a cross-section through the chest at the level of the eighth thoracic vertebra were generated. The imaging showed the heart and mediastinum in the midline between the left and right lungs with the heart encroaching on the left lung space as it does at this level. Also seen was the descending aorta just left and anterior to the vertebral body.
A nuclear magnetic resonance (NMR) image of a tumor in a live animal is reported. The field focusing NMR method or FONAR process that now achieves the tumor outline is described.
A protein fraction (A-L fraction) with characteristics reminiscent of muscle actin has been isolated from Escherichia coli. The A-L fraction undergoes reversible aggregation under the same conditions in which actin is polymerized and depends primarily on potassium for its polymerization. This fraction, upon electrophoresis on acrylamide gels in the presence of sodium dodecyl sulfate, exhibits a distinct peak at the characteristic molecular weight of 45,000. Passage of skeletal muscle myosin through the A-L fraction specifically removes this 45,000-molecular weight peak. Examination of the myosin by sodium dodecyl sulfate electrophoresis after the passage reveals a new band at the proper molecular weight. The A-L fraction from wild-type E. coli is compared with the protein from a potassium transport mutant. Important catalytic differences exist between the A-L fractions of the two strains. The A-L fraction from the mutant fails to polymerize in low-K media in the K+ concentration range in which the mutant fails to take up to K+. In low-K+ media, the parent strain accumulates potassium and the A-L fraction from this organism polymerizes. The cell swelling reaction of both strains has been studied. Parent cells swell during low-K+ uptake, whereas the mutant does not. It is construed from this that the differences in the characterization of the A-L fraction relative to that of the wild type are related to the loss of cell swelling in the mutant and hence to the loss in alkali cation selectivity. The possible role of contractile proteins in biological ion exchange is discussed.
Actin-like (A-L) fraction from normal E. coli was compared with the protein from a potassium-transport mutant strain, and the cell-swelling reaction of both strains was studied. Findings were: (a) The membrane fraction of the mutant by SDS electrophoresis is deficient in the A-L fragment relative to normal whereas the soluble supernatant contains an excess. (b) Important catalytic differences exist between the A-L fractions of the two strains. The parent strain accumulates potassium in low K+ and the A-L fraction polymerizes in low K+. But the A-L fraction from the mutant fails to polymerize in low K media in the K+ concentration region where the mutant fails at K+ uptake. (c) The parent cell swells during low K+ uptake whereas the mutant does not. It is constructed from this that the differences in the characterization of A-L fraction relative to normal are related to the loss of cell-swelling in the mutant and hence to the loss in alkali cation selectivity. Thus two physical mechanisms, one macroscopic and dependent on the Gregor relation for swelling equilibria in ion exchange resins, and one more microscopic based on the dielectric dependence of the coulomb force between ion pairs, could underly regulation of ion selectivity by cell swelling. A similar proposal is made for the regulation of electron transport and oxidative phosphorylation in mitochondria. These findings and interpretations justify a new hypothesis to the effect that cell hydration is regulated by contractile proteins. The hypothesis fits together important observations hitherto unexplained, to wit: (1) The "missing link" as to the role of intermediate metabolism in biological ion exchange. (2) The swelling of bacterial protoplasts and its relation to (Mg2 + Ca2+)ATPase activity. (3) The swelling-contraction cycles of mitochondria and their role in electron transport. (4) The role of ATPase's in transport. (5) The significance of actomyosin fibers in nerve endings. (6) The significance of altered actomyosin structures in the cancerous cell.
A protein fraction with actin-like characteristics has been isolated from E. coli. The fraction (referred to as A-L fraction) undergoes reversible increases in molecular weight under the same catalytic conditions that polymerize actin, exhibits a distinct peak on SDS electrophoresis at the characteristic molecular weight for actin, depends primarily on potassium for its polymerization, and is not "polymerized" by sodium. A-L fraction in the monomeric form was eluted in the void volume of a Sepharose 6B column, suggesting a large Stoke's radius and a molecular weight in excess of 400,000. The fraction contained 30% RNA by weight that proved refractory to experimental efforts at removal.
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