Fructose 1,6-bisphosphate aldolase from rabbit muscle. The isomerization of the enzyme-dihydroxyacetone phosphate complex.
The formation and dissociation of the aldolase-dihydroxyacetone phosphate complex were studied by following changes in A240 [Topper, Mehler & Bloom (1957), Science 126, 1287-1289]. It was shown that the enzyme-substrate complex (ES) slowly isomerizes according to the following reaction: (formula: see text) the two first-order rate constants for the isomerization step being k+2 = 1.3s-1 and k-2 = 0.7s-1 at 20 degrees C and pH 7.5. The dissociation of the ES complex was provoked by the addition of the competitive inhibitor hexitol 1,6-bisphosphate. At 20 degrees C and pH 7.5, k+1 was 4.7 X 10(6)M-1-S-1 and k-1 was 30s-1. Both the ES and the ES* complexes react rapidly with 1.7 mM-glyceraldehyde 3-phosphate, the reaction being practically complete in 40 ms. This shows that the ES* complex is not a dead-end complex. Evidence was also provided that aldolase binds and utilizes only the keto form of dihydroxyacetone phosphate.
D000818:Animals; D004099:Dihydroxyacetone Phosphate / Q000378:metabolism*; D005292:Ferricyanides / Q000378:metabolism; D005634:Fructose-Bisphosphate Aldolase / Q000378:metabolism*; D005985:Glyceraldehyde / Q000378:metabolism; D006598:Hexosediphosphates / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D011817:Rabbits; D014306:Trioses / Q000378:metabolism*
D005292:Ferricyanides; D006598:Hexosediphosphates; D014306:Trioses; D005985:Glyceraldehyde; D004099:Dihydroxyacetone Phosphate; D005634:Fructose-Bisphosphate Aldolase