Molecular chaperones are present in the thylakoid lumen of pea chloroplasts

A soluble protein fraction was obtained from pea chloroplast thylakoids, which represents highly enriched lumenal components. Using antisera against chaperonin 60 (cpn60), chaperonin 10 (cpn10) and the heat shock cognate protein of 70 kDa (hsc70) we are able to demonstrate, that the thylakoid lumen contains a separate set of molecular chaperones, which is distinct from the stromal one. In contrast to the alpha and beta subunits of cpn60 present in the stroma the lumen contains only one cpn60 isoform of distinct isoelectric point. Furthermore the lumenal cpn10 is of 'normal' size and not like its stromal counterpart of a double-domain tandem architecture. The immunoreactive hsc70 isoforms in the lumen seem also to be different from the stromal ones. Thus, chloroplasts seem to contain the largest number of molecular chaperone isoforms present in one organelle.