Proteins of the chloroplast and cytoplasmic ribosomes of Euglena

The proteins of chloroplast and cytoplasmic ribosomes, isolatedfrom Euglena gracilis, have been compared by electrophoresison SDS-polyacrylamide gels. The proteins of the cytoplasmicribosomes were more numerous and larger on the average thanthose of the chloroplast ribosomes. There were about 14 proteins detected in the small subunit ofthe chloroplast ribosome, ranging from 11,000 to 43,000 daltonsand 16 proteins of 10,000 to 36,000 daltons from the large subunit.The banding patterns of the proteins of the subunits were quitedistinct from each other. The subunits of the cytoplasmic ribosomes were obtained by dissociationof the monomer with EDTA, and in 100 mm and 500 mil KCl andthe effects of these conditions of dissociation on the proteinsof the subunits compared. Regardless of the means of dissociation,the small and large subunits each gave 20–21 proteinsranging from 10,000 to 49,000 daltons. However, a comparisonof scans of the subunits indicated a selective and partial strippingof ribosomal proteins by high salt and by EDTA; i.e. differentproteins were sensitive to the two treatments. Native subunits, presumed to occur free in the cytoplasm werealso isolated. In addition to the ribosomal proteins found insmall subunits obtained by dissociation, the native small subunitcontained substantial amounts of high-molecular-weight proteins. Small, variable amounts of high-molecular-weight proteins arealso associated with chloroplast ribosome subunits, but thequantities depend on the method of purification of the subunits.Because these components are virtually eliminated followingtwo cycles of density gradient centrifugation, we infer thatthey are adventitious. These observations reflect on the relative merit among severalreported methods of purification of chloroplast and cytoplasmicribosomes. ¹ Present address: Department of Biochemistry, College of Medicineand Dentistry of New Jersey, Piscataway, N.J. 08854, U.S.A. (Received May 13, 1975; )