Juntendo Medical Journal

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Actin and tropomyosin were labeled with fluorescent thiol reagents, N- (1-anilinonaphthy 1-4) maleimide (ANM) or N- (p- (2-benzimidazolyl) phenyl) maleimide (BIPM), and the transmission of the effect of Ca²⁺ from troponin to F-actin on the thin filament was studied fluorometrically. 1. The chemical modification of actin and tropomyosin did not essentially alter their physiological functions. 2. The fluorescence characteristics of labeled actin were altered by combination with H-meromyosin and by G-F transformation. On the other hand, those of labeled tropomyosin were altered by combination with actin or troponin. 3. The microenvironment around the thiol (s) bound with the dye in actin was appresiably hydrophobic. However, its polarity did not change by combination with tropomyosin or tropomyosin-troponin complex in the presence and absence of Ca²⁺. Under the same conditions, on the other hand, quantum yield and fluorescence lifetime significantly changed. The latter of the ANM-F-actin-tropomyosin-troponin complex was restored to the level for F-actin-tropomyosin complex by adding 10^-5 M CaCl₂, but the former was incompletely recovered. 4. The apparent Ca²⁺ -binding constant obtained from the change in lifetime, 1.3×10⁶ M, was in good agreement with the value reported on troponin alone. 5. Thermal dependence studies on the fluorescence polarization of ANM-F-actin revealed that a thermally activated portion and thermal transition of structure at 31°C appeared on addition of tropomyosin and/or troponin. On addition of Ca²⁺ to the complete system, the above phenomena completely disappeared. 6. Quantum yield of ANM-tropomyosin decreased by complex formation with either skeletal or cardiac troponin. Those of ANM-tropomyosin-troponin complexes further decreased by the same degree on addition of 10^-4M CaCl₂ or SrCl₂ in the presence of 1mM MgCl₂. From the above results it can be concluded that a conformation change in troponin first triggered by Ca²⁺-binding is transmitted to the actin molecule via tropomyosin without any leakage,.

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Effects of aging on the lipid metabolism of the liver were studied in 8 early newborn rats (0-4 days after birth), 11 late newborn rats (5-10 days after birth), and 15 infant rats (11-28 days after birth). Respiratory quotient (R. Q. : Warburg Manometer) and the amount of acetone bodies (Conway's Diffusion method) in the rat liver were measured in fasting and in 1, 2, 3, and 4 hours after the oral administration of corn oil. At the same time, blood glucose concentration (glucose oxidase method) was measured in each rat. In fasting state, the acetone bodies contents of the liver were more increased in the early newborn rat than in the late newborn and infant rats, while the R. Q. was lower in the early newborn rats. The rise in the acetone bodies contents of the liver after the oil administration were the lowest in the early newborn rats and the highest in the infant rats. In the early newborn rats, the changes in the R. Q. after the oil loading were lower than the other group of rats at each times and were biphasic with the initial increase followed by rapid decrease. Changes of the blood glucose levels after the oil administration increased more significantly in the early newborn rats than in the infant rats. It is suggested that the gluconeogenesis from lipid and fatty acid oxidation in the liver after the oral oil administration are more enhanced in the early newborn rats than the infant rats.

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