Hydrolysis of inositol trisphosphate by purified rat brain myelin.
Highly purified rat brain myelin was found to hydrolyze inositol 1,4,5-trisphosphate to inositol 1,4-bisphosphate, but subsequent hydrolysis of the latter, characteristic of whole brainstem, did not occur. Inositol 1,4,5-trisphosphate 5-phosphatase in myelin was approximately 33% of the level in microsomes and 127% that of the cytosolic fraction from brainstem. The myelin and microsomal enzymes had similar properties, as follows: activation by saponin, requirement for Mg2+ and similar Kact (0.16 and 0.13 mM), Km (8.7 +/- 2.5 and 7.0 +/- 1.0 microM), and pH optima (6.6-6.8). Vmax values were 11.2 +/- 1.0 and 26.3 +/- 2.0 nmol/mg/min for myelin and microsomes, respectively. A possible role for this enzyme in phosphoinositide-mediated signal transduction within myelin and its subcompartments is discussed.
Albert Einstein College of Medicine, Department of Neurology, Bronx, New York 10461.
J N
JN
Larocca
R W
RW
Ledeen
D000818:Animals; D001933:Brain Stem / Q000378:metabolism*; D006868:Hydrolysis; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D000072181:Inositol Polyphosphate 5-Phosphatases; D007700:Kinetics; D009186:Myelin Sheath / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism
D015544:Inositol 1,4,5-Trisphosphate; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases