Write the reaction mechanism and define the rate constants.

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To derive the velocity equation for a bi-substrate enzyme following a sequential mechanism, we will use the steady-state approximation for an ordered sequential Bi Bi mechanism, where substrate A binds first, followed by substrate B.

Step 1: Write the reaction mechanism and define the rate constants. Consider the ordered sequential Bi Bi mechanism: $E + A \underset{k_{-1}}{\overset{k_1}{\rightleftharpoons}} EA$ $EA + B \underset{k_{-2}}{\overset{k_2}{\rightleftharpoons}} EAB$ $EAB \overset{k_3}{\longrightarrow} E + P + Q$ Here, $E$ is the free enzyme, $A$ and $B$ are the