Separation and characterization of inner and outer envelope membranes of pea chloroplasts

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Abstract
A procedure for purifying the chloroplast envelope subfractionates it into 2 membrane fractions of comparable quantities. This procedure differs from previous ones in that the chloroplasts are ruptured by freezing and thawing in hypertonic medium rather than by osmotic shock. The 2 membrane fractions have qualitatively similar polar lipid composition, but differ in their content of individual lipids, specifically monogalactosyldiacylglycerol and phosphatidylcholine. The 2 fractions differ in their constituent polypeptides and in their appearance when examined by EM. The light (density = 1.08 g/ml) and heavy (density = 1.13 g/ml) membrane fractions were tentatively identified as the outer and inner envelope membranes, respectively.