Figure 4
Scheme of all the TK reactions accounting for competition between them. Designations are the same as in Figure 1. The reactions start with reversible binding of the free enzyme to ketose (with the elementary rate constants k1, k-1, k7, k-7, k6, k-6) and formation of the covalent enzyme-substrate complex followed by its splitting (k2, k-2, k8, k-8, k5, k-5) and formation of the covalently bound intermediate G ('active glycolaldehyde') and aldose, both localized in the active site of the enzyme. The split complex dissociates (k3, k-3, k9, k-9, k4, k-4) into the enzyme bound with active glycolaldehyde (EG) and the free molecule of aldose. Nine different isotope exchange fluxes are associated with these reactions, as explored in more detail in Figure 3.
xu5p + E → Exu5p → EGg3p 
EG 
EGrSp → Es7p → E + s7p
xu5p + E ← Exu5p ← EGg3p 
EG 
EGrSp ← ES ← E + s7p
xu5p + E → Exu5p → EGg3p EG 
EGe4p → Ef6p → E + f6p
xu5p + E ← Exu5p ← EGg3p EG 
EGe4p ← Ef6p ← E + f6p
s7p + E → Es7p → EGr5p 
EG EGe4p → Ef6p → E + f6p
s7p + E ← Es7p ← EGr5p 
EG EGe4p ← Ef6p ← E + f6p
xu5p+E↔Exu5p↔EGg3p↔EG+g3p
f6p+E↔Ef6p↔EGe4p↔EG+e4p
s7p+E↔Es7p↔EGrSp↔EG+r5p