ARTICLE

DENSITY GRADIENT SEPARATION OF SARCOTUBULAR VESICLES AND OTHER PARTICULATE CONSTITUENTS OF RABBIT MUSCLE

K. Seraydarian ¹ and W. F. H. M. Mommaerts ¹

¹ From the Department of Medicine of The Los Angeles County Heart Association Cardiovascular Research Laboratory, The University of California, Los Angeles

Separation of particulate matter in rabbit muscle extracts by differential centrifugation leads, in first approximation, to the isolation of fraction I (15,000 to 41,000 g) and fraction II (41,000 to 150,000 g). The former consists mainly of sarcotubular material, actively transporting calcium ions, and displaying relaxation factor activity. The latter is heterogeneous, shows little calcium accumulation, and contains factors both inhibiting and activating myofibrillar ATPase. Fraction I is resolved by density gradient centrifugation into 2 main subfractions. The lighter one represents sarcotubular material in the best state of preservation, with biochemical activities stable for weeks in the cold. The heavier one may consist of the same material in a less well preserved form. Upon aging, it develops an activating activity toward myofibrillar ATPase, when the relaxing effect has declined. Fraction II is resolved by density gradient centrifugation into 3 or more fractions, with some variability. Relaxing activity in terms of inhibition of myofibrillar ATPase predominates among the lighter subfractions, increase of ATPase among the heavier. The intrinsic ATPase of fraction II is activated by calcium ions, but there is little or no bulk accumulation of calcium oxalate. Nevertheless, its limited calcium uptake seems to suffice to explain its relaxing activity. The particulate material contains mucopolysaccharide and lipid. Most of the lipid in fraction I is phospholipid; in fraction II this is less than half, if calculated as lecithin. The unfractionated material contains an adenylcyclase. There is no acetylcholine esterase.

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This article has been cited by other articles:

• Rubin, B. B., Katz, A. M. (1967). Sodium and Potassium Effects on Skeletal Muscle Microsomal Adenosine Triphosphatase and Calcium Uptake. Science 158: 1189-1190 [Abstract]  
• Philpott, C. W., Goldstein, M. A. (1967). Sarcoplasmic Reticulum of Striated Muscle: Localization of Potential Calcium Binding Sites. Science 155: 1019-1021 [Abstract]  

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