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 (InsP(4)) mediates nuclear calcium signaling [Koppler P., Matter, N., & Malviya A. N. (1993) J. Biol. Chem. 268, 26248-26252], and a distinct high affinity InsP(4) binding site is identified with rat liver nuclei [Koppler, P., Mersel, M., & Malviya, A. N. (1994) Biochemistry 33, 14707-14713] as compared with other rat liver membrane fractions. A novel InsP(4) 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 InsP(4) 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 InsP(4) receptor consists of amino acids: PNHKNEIAGNFS.. The 74 kDa nuclear InsP(4) receptor protein is a distinct protein from the other InsP(4) receptors purified from other sources and documented in the literature.