A comparison of intrinsic endoplasmic reticulum membrane proteins in maturing seeds and germinated seedlings of castor bean.

The intrinsic membrane proteins of the endoplasmic reticulum from endosperm of maturing and germinated seedlings of castor bean (Ricinus communis) were studied. Preparations were simultaneously subjected to two-dimensional polyacrylamide gel electrophoresis. At least 30 separate proteins were distinguished by staining the gels with Coomassie R-250. The characteristic protein profiles obtained from 0.2 m KCl-washed membranes of each endoplasmic reticulum source are highly reproducible. Of these proteins, three to six that were present in maturing seed were found also in germinating seedlings. In general, the majority of membrane proteins from the endoplasmic reticulum of maturing seed were of a higher molecular weight than those from germinated seedlings.