Anomeric and other substrate specificity studies with myo-inositol-1-P synthase.
L-myo-Inositol-1-phosphate synthase has been found to have at least a 5-fold preference for the beta-anomer of its natural substrate D-Glc-6-P. The alpha-anomer appears to be an inhibitor of the reaction and may be converted to product as well. As well as showing an enzymatic preference for the equatorial C-1 hydroxyl of D-Glc-6-P, our results suggest that it is the pyranose form of D-Glc-6-P that binds to the enzyme and that ring-opening is an enzymatic step. We have also found D-2-dGlc-6-P, D-2-F-2-dGlc-6-P, and D-Man-6-P each to be both competitive inhibitors and substrates that are converted to inositol phosphates by the synthase. D-Allose-6-P is a weak inhibitor of the enzyme, but not a substrate. D-Gal-6-P is neither substrate nor inhibitor. Thus the specificity of the synthase with respect to single position epimers of D-Glc-6-P increases in the order C1 less than C2 much less than C3 less than C4.
D000818:Animals; D002238:Carbohydrate Epimerases / Q000378:metabolism*; D002417:Cattle; D008401:Gas Chromatography-Mass Spectrometry; D006600:Hexosephosphates / Q000494:pharmacology; D007536:Isomerism; D007700:Kinetics; D008297:Male; D007296:Myo-Inositol-1-Phosphate Synthase / Q000378:metabolism*; D013237:Stereoisomerism; D013379:Substrate Specificity; D013737:Testis / Q000201:enzymology*
D006600:Hexosephosphates; D002238:Carbohydrate Epimerases; D007296:Myo-Inositol-1-Phosphate Synthase