Introduction to Enzyme and Coenzyme Chemistry - E-Library Home

12 Non-Enzymatic Biological
Catalysis
12.1 Introduction
In the Wnal chapter I wish to address the question: are enzymes unique in their
ability to catalyse biochemical reactions The discovery of enzymes and the
elucidation of their function provides a basis for understanding how cellular
biological chemistry can be catalysed at rates suYcient to sustain life. Many of
the reactions catalysed by enzymes are highly complex, yet they can be rationalised
in terms of selective enzyme–substrate interactions and well-precedented
chemical reactions. Could such selective catalysis be carried out by other
biological macromolecules The answer is yes: we shall meet examples of
naturally occurring ribonucleic acid (RNA) molecules capable of catalysing
selective self-splicing reactions, and we shall see how the immune system can
be used to produce catalytic antibodies.
Finally, a challenging problem for the biological chemist is: if you think you
understand how enzymes work, can you design synthetic molecules capable of
enzyme-like catalytic properties This is an exciting area of current research,
and we shall see a few ingenious examples of how this problem has been
addressed.
12.2 Catalytic RNA
Ribonucleic acid is an important cellular material involved in various aspects of
protein biosynthesis. There are three types of RNA which are found in all cells:
messenger RNA (mRNA) into which the deoxyribonucleic acid (DNA) sequence
of a gene is transcribed before being translated into protein; transfer
RNA (tRNA) which is used to activate amino acids for protein biosynthesis;
and ribosomal RNA (rRNA) which comprises the ribosome protein assembly
apparatus. Thus, information transfer and cellular structures were thought in
the 1970s to be the only functions of RNA.
In the early 1980s the groups of Cech and Altman reported the startling
discovery that certain RNA molecules were capable of catalysing chemical
reactions without the assistance of proteins. The Wrst catalytic RNA (or ‘ribozyme’)
to be identiWed was found in the large sub-unit ribosomal RNA of a
ciliated protozoan Tetrahymena thermophila. This RNA molecule has the remarkable
ability to cut itself out of a larger piece of RNA, leaving a shortened
RNA template which is subsequently used for protein biosynthesis. This
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