Calbindin28kDa and calbindin30kDa (calretinin) are substantially localised in the particulate fraction of rat brain.

Calbindin28kDa is implicated in cytosolic calcium transport and calciprotection functions, principally as a mobile calcium buffer. Using immunoblotting, we have found that 36% of total calbindin28kDa is in the particulate fraction of rat brain. Particulate calbindin28kDa was located both within and outside organelles and required detergent for solubilisation. Equivalent observations were made for calbindin30kDa, 27% of which was insoluble. These findings indicate that a substantial proportion of calbindin does not function as a mobile calcium buffer, and perhaps instead has a calcium signalling role through target ligands in the insoluble cellular fraction.