Abstract
Summary Isolated spinach chloroplasts were osmotically disrupted and fractioned by centrifugation in two discontinuous sucrose gradients. Ultrastructural investigation of the different fractions in the first gradient showed the presence of chloroplast envelopes and plastoglobules in fraction 1, enriched stroma thylakoids in fraction 2 and fraction 3 contained stacks of grana thylakoids. Stroma thylakoids coherent with grana thylakoids were typical for the sediment fraction. Further purification of the envelope membranes (fraction 1) in a second continuous sucrose gradient resulted in one pure envelope fraction (fraction 1 b) with a buoyant density of 1.12 g/cm 3 . It could be demonstrated by comparison of membrane lengths from different fractions that the length distribution of isolated envelope membranes is different from grana or stroma thylakoids.
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