GRP94 (endoplasmin) co-purifies with and is phosphorylated by Golgi apparatus casein kinase.

A phosphorylatable protein band of about 94 kDa (as judged by SDS-PAGE) which co-purifies and co-immunoprecipitates with Golgi apparatus casein kinase (G-CK) from rat lactating mammary gland has been shown by mass spectrometric sequence analysis to be identical or very similar to the glucose-regulated protein, GRP94. GRP94 is also readily phosphorylated by G-CK (K(m)=0.2 microM) at seryl sites which are different from the sites affected by casein kinase-2 (CK2) in the same protein.

Proteolysis of liver plectin by mu-calpain.

Rat liver plectin was found to be mainly associated with plasma membrane fractions enriched in junctional complexes. The membrane-associated plectin has been partially isolated. Plectin co-purifies with a 200 kDa polypeptide which, on the basis of sequence homology, has been identified as a myosin like-protein.