Stabilization of glucosaminephosphate synthase from rat liver by hexose 6-phosphates. Properties and interconversion of two molecular forms.
Glucosaminephosphate synthase (glucosaminephosphate isomerase (glutamine-forming), EC 5.3.1.19) prepared from rat liver by extraction in the presence of glucose 6-phosphate (Glc-6-P) followed by precipitation with (NH4)2SO4 is susceptible to digestion by trypsin. This enzyme, designated form A, can be converted to tryptic-insusceptible form B upon incubation with Glc-6-P or fructose 6-phosphate (Fru-6-P) at 37 degrees C. The two forms also differ in the degree of activation by dithiothreitol, the degree of inhibition by methyl-glyoxal and the behavior on DEAE-Sephadex and Sephadex G-200 column chromatography. During purification with DEAE-Sephadex followed by hydroxyapatite, form B is converted to form A if Fru-6-P is absent and form A to form B if Fru-6-P is present. The two forms are therefore intercovertible. Under the conditions of purification, form B is more stable than form A, since the purity and yield of the final product are greater with form B than with form A. These findings suggest that the two forms of glucosaminephosphate synthase differ conformationally and that the equilibrium position depends on the concentration of Fru-6-P. Glc-6-P is effective only when it gives rise to Fru-6-P by mediation of glucose-phosphate isomerase.
D000818:Animals; D002238:Carbohydrate Epimerases / Q000378:metabolism*; D004355:Drug Stability; D005636:Fructosephosphates / Q000494:pharmacology; D005958:Glucosephosphates / Q000494:pharmacology; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000302:isolation & purification / Q000378:metabolism*; D006598:Hexosediphosphates / Q000494:pharmacology; D006600:Hexosephosphates / Q000494:pharmacology*; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D008970:Molecular Weight; D051381:Rats; D013997:Time Factors; D014357:Trypsin
D005636:Fructosephosphates; D005958:Glucosephosphates; D006598:Hexosediphosphates; D006600:Hexosephosphates; D007527:Isoenzymes; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); D014357:Trypsin; D002238:Carbohydrate Epimerases