Role of lipids in sarcoplasmic reticulum: A higher lipid content is required to sustain phosphoenzyme decomposition than phosphoenzyme formation |
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| Affiliation: | 1. Department of Muscle Research, Boston Biomedical Research Institute, and Department of Neurology, Harvard Medical School, Boston, Massachusetts 02114, USA;2. Centro de Estudios Científicos de Santiago, Casilla 16443, Santiago 9, Chile;3. Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad de Chile, Casilla 137-D, Correo Central, Santiago, Chile;1. Laboratory of Microenvironmental and Metabolic Health Science, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan;2. Department of Nutritional Science, Okayama Prefectural University, 111 Kuboki, Soja, Okayama 719-1197, Japan;1. Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry (NCNP), Kodaira, Tokyo, 187-8502, Japan;2. Department of Lipid Signaling, National Center for Global Health and Medicine (NCGM), Shinjuku-ku, Tokyo, 162-8655, Japan;3. Institute of Microbial Chemistry, Shinagawa-ku, Tokyo, 141-0021, Japan;4. Department of Lipid Life Science, National Center for Global Health and Medicine (NCGM), Shinjuku-ku, Tokyo, 162-8655, Japan;5. Department of Lipid Medical Science, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan |
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| Abstract: | Enzyme preparations with variable phospholipid contents were obtained by removing lipids from sarcoplasmic reticulum with deoxycholate. Preparations containing from 90 to 37 phospholipids per enzyme showed normal values of both Ca2+-ATPase activity and steady-state phosphoenzyme levels. Fractions containing 37 to 23 phospholipids per enzyme had a reduced ATPase activity but normal phosphoenzyme levels, showing that in this range of lipid content the ATPase reaction is inhibited in a reaction step subsequent to phosphoenzyme formation but prior to phosphoenzyme decomposition. Delipidation below 23 lipids per enzyme caused a marked reduction of the amount of phosphoenzyme formed, so that although both reactions require lipids, fewer lipids are required for phosphoenzyme formation than for decomposition. The effect of lipid removal could be completely reversed by readdition of lipids to fractions containing more than 11 lipids per enzyme. It is proposed that phosphoenzyme formation requires full occupancy of a boundary domain of 23 lipids per enzyme, and that the selective inhibition of phosphoenzyme decomposition at higher lipid contents is caused by a decrease in the rotational mobility of the enzyme. |
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