Identification of chiro-inositol and its formation by isomerization of myo-inositol during hydrolysis of glycosylphosphatidylinositol-anchored proteins.
myo-Inositol has been believed to be a sole inositol isomer existing in phosphatidylinositol (PI) and related derivatives. In this experiment, chiro-inositol, an inositol isomer other than myo-inositol, was identified in hydrolytic products from several GPI-anchored proteins. The chiro-inositol contents in several different GPI-anchored proteins including 5'-nucleotidase of bovine liver and alkaline phosphatase of mouse NS-1 varied with hydrolytic conditions of these GPI anchor. Isomerization of 20-60% of myo-inositol occurred on the hydrolysis in 6 N HCl solution. Under the hydrolytic conditions of a HCl gas stream in place of solution, however, isomerization was very low (less than 0.1%). Even in the hydrolysis under HCl gas stream, existence of CNBr accelerated the isomerization of inositol in GPI up to 70-95%. In the hydrolysis of phosphatidylinositol or myo-inositol 1-phosphate, however, a significant amount of chiro-inositol was not detected in 6 N HCl solution or in the existence of CNBr under the HCl stream. These facts indicated that isomerization occurred during the hydrolysis of the GPI anchor, when myo-inositol is substituted by glucosamine at 6-OH and is substituted by phosphate at 1-OH. It also suggested that the former identification of chiro-inositol in GPI structure in the various reports might be due to isomerization.
Taguchi
R
R
Faculty of Pharmaceutical Sciences, Nagoya City University, Aichi, Japan.
Yamazaki
J
J
Tsutsui
Y
Y
Ikezawa
H
H
D015720:5'-Nucleotidase / Q000737:chemistry; D000818:Animals; D002417:Cattle; D002460:Cell Line; D008401:Gas Chromatography-Mass Spectrometry; D017261:Glycosylphosphatidylinositols / Q000737:chemistry*; D007294:Inositol / Q000096:biosynthesis* / Q000737:chemistry; D051379:Mice; D011506:Proteins / Q000737:chemistry; D013237:Stereoisomerism
D017261:Glycosylphosphatidylinositols; D011506:Proteins; D007294:Inositol; D015720:5'-Nucleotidase