238

6

Bioinorganic Chemistry: A Short Course, Second Edition, by Rosette M. Roat-Malone
Copyright © 2007 John Wiley & Sons, Inc.

GROUP I AND II METALS IN

BIOLOGICAL SYSTEMS: GROUP II

6.1 Introduction,

Chapter 5 discussed homeostasis for Groups I and II metal ions and described
a number of biomolecules containing Group I metal ions, concentrating on
Na+ /K + ATPases and potassium ion channels. Chapter 6 will discuss Group II
metal ions in biomolecules, concentrating on magnesium ions in catalytic RNA
and on two calcium - containing biomolecules — calmodulin and Ca 2+ - ATPase.

6.2 Magnesium and Catalytic RNA,

6.2.1 Introduction,

Prior to 1982, it was believed that biological catalytic species were solely con-
stituted of amino acid chains — that is, proteins or, more correctly, enzymes.
However, in that year T. R. Cech and colleagues reported the fi rst catalytic
RNA, calling it a ribozyme.^1 It is now known that ribozyme sequences are
small parts of larger stretches of messenger or ribosomal RNA. Many reac-
tions carried out by ribozymes are cleavage or ligation reactions and are part
of post - transcriptional modifi cation processes that lead to the mature RNA,
DNA, or protein sequences — that is, maturation. The fi rst characterized ribo-
zyme was the self - splicing intron of the Tetrahymena pre - rRNA.^2 Researchers
discovered that the Tetrahymena pre - rRNA spliced out its intron and