Since water inhibits the formation of
peptide bonds, the first step to create a peptide often involves removing water. Fox
successfully created chains of amino acids by heating a purified concentration of amino
acids to 150 degrees Celsius for about 14 hours. At this temperature, water and other
volatile compounds vaporize. This is important because when a peptide bond forms, a single
water molecule is also produced. The heat drives this molecule off forcing the reaction
forward because without water it cannot go backwards.
Fox obtained very long chain when he included the amino acids glutamate,
aspartic acid and lysine. Fox called the amino acid chains formed by heating, protenoids.
They are also called thermal proteins. They are different from normal proteins in two
important ways 1) thermal proteins contain both the D and L isomers and 2) the peptide
bonds that form are very unusual. The side chains associated with lysine, glutamate and
aspartate form over ½ of the peptide bonds.1 This second feature has led most
origin of life researchers to drop protenoids as a viable candidate for the first living
protein. Stanley Miller in particular has criticized thermal proteins as unlikely
candidates because the conditions necessary to form them probably rarely exist. The
temperature has to fall within a narrow range (150-180 deg C), and if the heating lasts
too long (more than a day), then the thermal proteins are destroyed.2
Furthermore, given that amino acids will not form thermal proteins without a very high
concentration of aspartate, glutamate, or lysine leads to another question, how do
proteins with reasonable concentrations of these 3 amino acids form in the soup?
Protenoids do have several significant advantages over all the other
processes that will be considered in this chapter. The temperature of the reaction is high
enough to prevent many cross reactions.
Formic acid and formaldehyde are always chemicals found in the Miller water
trap. Formaldehyde is so reactive that it probably combines with the amino acids and drops
out of the solution. Formic acid can react with amino acids to form an amide bond. Because
formic acid only has a C-terminus (no N-terminus), this reaction is a chain terminator.
Once it happens, the chain cannot grow by adding another amino acid to formic acid. Since
formic acid and formaldehyde boil at very low temperatures, Fox’s approach vaporizes
both.
Given 5 billion years, a few thermal proteins may have had a chance to form.
In this respect, thermal proteins are unique. While they are not biological precursors
(due to the unconventional peptide bonds), they do at least have a chance of existing.
Whether or not they have anything to do with the origin of life is debatable.
Next: Short Peptides in Water (Clay Catalyst)
Previous: Miller Spark Chamber
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