The human and rat forms of multiple inositol polyphosphate phosphatase: functional homology with a histidine acid phosphatase up-regulated during endochondral ossification

We have derived the full-length sequences of the human and rat forms of the multiple inositol polyphosphate phosphatase (MIPP); their structural and f unctional comparison with a chick histidine acid phosphatase (HiPER1) has r evealed new information: (1) MIPP is approximately 50% identical to HiPER1, but the ER-targeting domains are divergent; (2) MIPP appears to share the catalytic requirement of histidine acid phosphatases, namely, a C-terminal His residue remote from the RHGxRxP catalytic motif; (3) rat MIPP mRNA is u pregulated during chondrocyte hypertrophy. The latter observation provides a contest for proposing that MIPP may aid bone mineralization and salvage t he inositol moiety prior to apoptosis. (C) 1999 Federation of European Bioc hemical Societies.