805. Cyclitols. Part X. Myoinositol phosphates

Ragan

Watling

et al. 1988

177

149

1. An inositol monophosphatase was purified to homogeneity from bovine brain. 2. The enzyme is a dimer of subunit Mr 29,000. 3. The enzyme hydrolyses both enantiomers of myo-inositol 1-phosphate and both enantiomers of myo-inositol 4-phosphate, but has no activity towards inositol bisphosphates, inositol trisphosphates or inositol 1,3,4,5-tetrakisphosphate. 4. Several non-inositol-containing monophosphates are also substrates. 5. The enzyme requires Mg2+ for activity, and Zn2+ supports activity to a small extent. 6. Other bivalent cations (including Zn2+) are inhibitors, competitive with Mg2+. 7. Phosphate, but not inositol, is an inhibitor competitive with substrate. 8. Li+ inhibits hydrolysis of inositol 1-phosphate and inositol 4-phosphate uncompetitively with different apparent Ki values (1.0 mM and 0.26 mM respectively).

Section: Materials and Methods Materialsmentioning

confidence: 99%

The purification and properties of myo-inositol monophosphatase from bovine brain

Ragan

Watling

et al. 1988

177

149

“…Frozen bovine brains were obtained from Imperial Laboratories, Salisbury, Wilts., U.K. DL-Ins(1,3,4,5)P4 and Ins(1,3)P2 were prepared as described by Billington & Baker [23], DL-Ins(3,4)P2 and DL-Ins(1,4)P2 as described by Angyal & Tate [24], and inositol monophosphates as described by Billington et al [25]. [Ins-2-3H(n)]-Ins(1,3,4,5)P4 (5 Ci/mmol) was obtained from New England Nuclear (Du Pont, Stevenage, Herts., U.K.).…”

Section: Methodsmentioning

confidence: 99%

Purification and properties of inositol-1,4-bisphosphatase from bovine brain

Reid

Jackson

et al. 1988

Inositol-1,4-bisphosphatase has been purified 13,000-fold from bovine brain supernatant. The enzyme is monomeric, with an apparent subunit Mr of 40,000. Maximal hydrolytic rates were observed in Tris buffer, pH 7.8, in the presence of 9 mM-Mg2+. The enzyme acted as a 1-phosphatase, hydrolysing both inositol 1,4-bisphosphate [Ins(1,4)P2] (Km 0.04 mM) and inositol 1,3,4-trisphosphate [Ins(1,3,4)P3] (Km 0.5 mM) to inositol 4-phosphate and inositol 3,4-bisphosphate respectively. Li+ inhibited the hydrolysis of both substrates in an uncompetitive manner, with apparent Ki values of 9.63 mM and 0.46 mM for Ins(1,4)P2 and Ins(1,3,4)P3 respectively.

“…Inositol monophosphates were synthesized as described by Billington et al [25], DL-Ins(1,4)P2 and DL-Ins(3,4)P2 as described by Angyal & Tate [27], and Ins(1,3)P2 was synthesized by the method of Billington &…”

Section: Substratesmentioning

confidence: 99%

The dephosphorylation of inositol 1,4-bisphosphate to inositol in liver and brain involves two distinct Li+-sensitive enzymes and proceeds via inositol 4-phosphate

Ragan

Watling

et al. 1988

1. Hydrolysis of both enantiomers of inositol 1-phosphate and both enantiomers of inositol 4-phosphate to inositol is inhibited by LiCl in liver and brain. 2. The phosphatase activity is predominantly soluble. 3. Inositol 1,4-bisphosphate is also hydrolysed by the soluble fraction of liver and brain. 4. Bisphosphatase activity is inhibited by LiCl, but is less sensitive than monophosphatase activity. 5. The product of bisphosphatase in liver and brain is inositol 4-phosphate.