High affinity inositol 1,3,4,5-tetrakisphosphate receptor from rat liver nuclei: purification, characterization, and amino-terminal sequence.

Inositol 1,3,4,5-tetrakisphosphate (InsP4) mediates nuclear calcium signalling [Köppler P., Matter, N., Malviya A.N. (1993) J. Biol. Chem. 268, 26248-26252], and a distinct high affinity InsP4 binding site is identified with rat liver nuclei [Köppler, P., Mersel, M., & Malviya, A.N. (1994) Biochemistry 33, 14707-14713] as compared with other rat liver membrane fractions. A novel InsP4 receptor protein derived from rat liver nuclei has been purified to apparent homogeneity employing preparative isoelectric focusing, electrophoretic mobility, nondenaturating polyacrylamide gel electrophoresis, and electroelution. Isoelectric focusing indicated an isoelectric pH around 4.3 +/- 0.2 which was further confirmed by bidimensional electrophoresis. The high affinity nuclear InsP4 receptor was identified as a 74 kDa protein both on the SDS-PAGE and on the bidimensional electrophoresis. Partial microsequence analysis showed that the N-terminal end of nuclear InsP4 receptor consists of amino acids: PNHKNEIAGNFS. The 74 kDa nuclear InsP4 receptor protein is a distinct protein from the other InsP4 receptors purified from other sources and documented in the literature.