Preparation of vesicular relaxing factor from bovine heart tissue

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Abstract
A particulated fraction, consisting mainly of protein and phospholipid, was prepared from bovine heart muscle by differential centrifugation. This microsomal suspension was found to inhibit superprecipitation of myosin B and to have a strong calcium-binding capacity. Although the preparation appeared to be very labile, a constant degree of activity was obtained by adding α-tocopherol before the homogenization of cardiac tissue. Evidence was gained for an interaction of calcium ions with synthetic lecithin in water suspensions. However, this interaction was competitively inhibited by the presence of magnesium and ATP, which are required cofactors for calcium binding by microsomes. It is proposed that in cardiac muscle, sarcoplasmic reticulum plays essentially the same role as in skeletal muscle.

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