Ribozyme molecules

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. 

Zhuang, XW, Kim, H, Pereira, MJB, Babcock, HP, Walter, NG,and Chu, S, Correlating structural dynamics and function in single ribozyme molecules. Science 296 (2002) 1473-1476. 

Figure 6.17 Docked states have a strong memory effect, as indicated by FRET time traces of single rlbozyme-substrate complexes, (a) Memory effect of the undocking kinetics where a molecule rarely switches between different docked states. (b)An example of memory loss after 3 h. The excitation was shut off after 500 s for 3 h to prevent dye photobleaching. Reprinted with permission from Zhuang etal., Correlating structural dynamics and function in single ribozyme molecules. Science 296 (2003) 1473-1476. Copyright 2002 AAAS.

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