Premium
Activity and distribution of phosphoinositidase C in rat sciatic nerve
Author(s) -
Mathew J.,
Date S.,
Eichberg J.
Publication year - 1992
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490330115
Subject(s) - sciatic nerve , distribution (mathematics) , chemistry , medicine , mathematics , mathematical analysis
The hydrolysis of phosphatidylinositol‐4,5‐bisphosphate (PIP 2 ) by rat sciatic nerve cytosolic phosphoinositidase C [phosphoinositide‐specific phospholipase C (PIC)] was studied at neutral pH and at ionic concentrations that approximate intracellular conditions. The principal water‐soluble product formed was shown to be inositol trisphosphate by anion exchange chromatography. The maximum hydrolysis rate (2.5 nmol/min/mg protein) was achieved at < 100 nM Ca 2+ . Hydrolysis was markedly increased to 15 nmol/min/mg protein by inclusion of K + in the reaction mixture. In the presence of 200 mM K + , the optimum Ca 2+ was increased to approximately 600 nM. Higher Ca 2+ concentrations progressively inhibited PIP 2 hydrolysis. Mg 2+ also inhibited the reaction, but the presence of equimolar amounts of ATP and Mg 2+ had no effect. Appreciable degradation of phosphatidylinositol‐4‐phosphate (PIP) also occurred in the nanomolar Ca 2+ range, whereas breakdown of phosphatidylinositol (PI) required millimolar Ca 2+ . The presence of PIP but not PI inhibited PIP 2 hydrolysis. Upon subcellular fractionation of nerve, more than 50% of recovered PIC activity was in the cytosol and about 20% was located in a myelin‐enriched fraction. Using PIP 2 as substrate, PIC activities in nerves from normal and streptozotocin‐induced diabetic animals were not different. However, the myelin‐associated enzyme from diabetic animals was more labile to freezing and thawing. © 1992 Wiley‐Liss, Inc.