Possible extremes

The potential extreme is that Iodine can replace methyl groups.


http://www.anst.uu.se/hanslund/Nuklidteknik/kompendium.pdf
, page 86
"However, small molecules, such as amino acids, were found to lose their specific biological activity when labeled with such nuclides. 125I-thyrosine could be transported across the cell membrane but could not be incorporated into the proteins, i.e. the membrane transport system was fooled but not the more specific tRNA-system. Other molecules, such as 125I-IUdR, could mimic the biogenic molecule thymidine and were incorporated into the DNA-molecule but at a lower rate. In this case the Iodine replaces a methyl-group, a quite dramatic change. However, the Iodine atom has about the same van der Waal radius as the methyl-group, which is enough to trick the biology."


http://www.proteinscience.org/cgi/reprint/6/10/2097.pdf
, page 6
"Although thymine is bound tightly, it does not fill its binding
pocket completely. In complex TK:ADP:dTMP, thymine leaves a
non-polar 35 A3 void close to its C5 position (Fig. 6A). In
TK:ADP:5-iodo-dUMP, the large iodine replaces the smaller methyl
group without steric hindrance and still leaves a void of 17 A3
(Fig. 6B)."

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The displaced methyl groups could result in under-methylation of some biochemical reactions, and over-methylation of other biochemical reactions. The potential extremes of over- and under-methylation are described at the following web site.

http://www.nutritional-healing.com.au/content/articles-content.php?heading=Ma...
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