Enzymatic catalysis Michaelis-Menten constant

Figure 6 Enzymatic catalysis of proteolysis. The overall reaction rate is determined by K2 and the Michaelis-Menten constant is approximately equal to the dissociation constant Alj/Mi of the enzyme-substrate complex (38).

The enzymatic activity of the L-19 IVS ribozyme results from a cycle of transesterification reactions mechanistically similar to self-splicing. Each ribozyme molecule can process about 100 substrate molecules per hour and is not altered in the reaction therefore the intron acts as a catalyst. It follows Michaelis-Menten kinetics, is specific for RNA oligonucleotide substrates, and can be competitively inhibited. The kcat/Km (specificity constant) is 10s m- 1 s lower than that of many enzymes, but the ribozyme accelerates hydrolysis by a factor of 1010 relative to the uncatalyzed reaction. It makes use of substrate orientation, covalent catalysis, and metalion catalysis—strategies used by protein enzymes. 

The formulation of Michaelis and Menten, which treats the first step of enzyme catalysis as an equilibrium (Eq. (3.4)), makes unwarranted and unnecessary assumptions about the rate constants (Eq. (3.3)). Indeed, as we now know, the rate constants K Jta. and can vary within very wide limits in many, if not the most, enzymatic reactions. 

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