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Secretion Granules of the Rabbit Parotid. Selective Removal of Secretory Contaminants from Granule Membranes

J. David Castle and George E. Palade
The Journal of Cell Biology
Vol. 76, No. 2 (Feb., 1978), pp. 323-340
Stable URL: http://www.jstor.org/stable/1608410
Page Count: 18
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Secretion Granules of the Rabbit Parotid. Selective Removal of Secretory Contaminants from Granule Membranes
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Abstract

A membrane subfraction obtained from secretion granules isolated from rabbit parotid has been shown to be contaminated by residual secretory proteins to an estimated level of 25-30% of its total protein. In the present study an additional contaminant has been identified by improved mixing experiments and by comparative peptide mapping of specific polypeptides recovered from gels of membrane and content subfractions. This contaminant coelectrophoreses with (and probably comprises the bulk of) the majority component of the membrane subfraction (mol wt ∼40,000). The contaminating polypeptides can be removed to a large extent by treating the membranes with low concentrations of saponin in the presence of 0.3 M Na2 SO4. Although this treatment disrupts the typical bilayer structure of the granule membrane, it does not appear to cause dissociation of its phospholipids or bona fide membrane proteins.

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