CALRETICULIN IS THE MAJOR CA2+ STORAGE PROTEIN IN THE ENDOPLASMIC-RETICULUM OF THE PEA PLANT (PISUM-SATIVUM)

A 56kDa protein with high similarity in its N-terminal amino acid sequence to animal calreticulin and 100% homology with the N-terminal amino acids of spinach calreticulin has been identified in seeds of the pea plant (Pisum sativum). A new purification procedure is described by which the calreticulin-like protein was selectively solubilized by incubation with deoxycholate and HgCl2 from microsomes enriched for endoplasmic reticulum. Following Mono Q ion exchange chromatography of the deoxycholate extract by fast protein liquid chromatography, the calreticulin-like protein was obtained in nearly pure form. This purified protein is similar to animal calreticulin in apparent mass, characteristic blue staining with Stains-all dye and calcium-binding ability. In addition, this protein is recognized only by affinity purified antibodies against rabbit calreticulin and is not recognized by anti-calsequestrin antibodies. Our data suggested that calreticulin rather than calsequestrin functions as the Ca2+-storage protein in the endoplasmic reticulum of pea plants. (C) 1995 Academic Press, Inc.