Lipid granules of fat-storing cells (FSC) were isolated from rats fed a diet containing physiological amounts of vitamin A. High-pressure liquid chromatography demonstrated 160μg retinyl palmitate and 0.25μg retinol in 1mg(dry weight) of isolated lipid granules. From 20 to 35% of retinyl palmitate in the liver was recovered in the lipid granular fraction. It is concluded that the lipid granules of FSC are the primary storage site for vitamin A in the liver.
Conformational change induced by Mg2+-ATP in the local area containing a specific thiol group, SH2, in skeletal myosin was regulated by physiological level of free Ca2+ concentration (pCa ranging from 8 to 4) . The curve relating conformational change to pCa in the presence of Mg2+-ATP has a characteristic sigmoid shape, showing an inflection point at pCa 5. This result suggests the presence of a Ca2+-dependent regulatory mechanism in skeletal myosin.