Comparison of the Molecular Weights of Proteins Synthesized by Isolated Chloroplasts with Those Which Appear during Greening in Zea mays

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Abstract
The proteins of prolamellar bodies of etioplasts and of thylakoid membranes of greening and mature chloroplasts from Z. mays were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Three classes of proteins were distinguished: those present in etioplasts and disappearing during greening, those absent in etioplasts and appearing during greening and those present in both etioplasts and chloroplasts. The largest number of proteins belonged to this last class. The MW of chloroplast thylakoid proteins were compared to the MW of the membrane-associated proteins synthesized by isolated, mature choloroplasts. Thirteen of the 15-20 membrane-bound proteins made by isolated chloroplasts corresponded in size to proteins present in chloroplasts. Most of the 13 are present in both etioplasts and chloroplasts although a few were the same size as proteins which increase during greening. Production of most of the membrane proteins made in the plastids is not stringently regulated by light in vivo. The polypeptide subunits of the light-harvesting pigment-protein complex, the most abundant proteins of the chloroplast thylakoids, were absent from etioplasts. They were not synthesized by isolated chloroplasts.

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