> Hi Kevin. I have three questions. First let me apologize for asking
> even though I haven't yet been able to read all the info you have
> provided. I really appreciate the effort you've expended. When I
> get ready to catch up on Fox I'll have all the info I need to
> get started.
No need to apologize. I don't mind answering questions, provided the person
asking them is motivated by a desire to learn.
> 1) One of the most oft mentioned criticisms of Fox's scenario
> is the "extra-large portions" of glysine or whatever required.
> Could you tell me once again the reference establishing your
> statement above?
MA Saunders and DL Rohlfing (1972), "Polyamino Acids: Preparation from
Reported Proportions of 'Prebiotic' and Extraterrestrial Amino Acids,"
Science 176, 172-173. In this paper, one of the mixtures tested was based on
a Miller-Urey type of experiment and contained only 0.3% aspartate and 0.5%
glutamate, with no lysine. It did, however, contain 50.6% glycine. Because
it made proteinoids, Rohlfing concluded that glycine could promote
copolymerization. Fox, however, never accepted that result, though he never
challenged it either. To my knowledge no one has tried to copolymerize amino
acids in the complete absence of aspartate, glutamate or lysine but in the
presence of glycine to test this issue. Until this is done, these results
support two simultaneous conclusions: glycine alone is sufficient for
copolymerization, or as little as 1% dicarboxylic acid is sufficient. It may
even be that both are occurring at the same time. A reasonable experiment
would be to use a mixture of amino acids consisting of 50% glycine and 50%
equimixture of all amino acids except aspartate, glutamate or lysine, then to
use the same mixture except that the 50% equimixture would now contain half a
percent of aspartate and half a percent of glutamate but still no lysine,
followed by a third mixture in which the equimixture contains 1% lysine but
no aspartate or glutamate. This experiment would not only determine if
glycine alone can promote copolymerization, but will also determine if very
small proportions of trifunctional amino acids like aspartate, glutamate or
lysine can enhance the results obtained from glycine.
SW Fox and TV Waehneldt (1968), Biochimica et Biophysica Acta 160, 246. I
have not been able to read this paper yet, but the results are summarized in
Fox and Dose, _Molecular Biology and and the Origin of Life_, Revised Edition
(1977). The authors used a number of different amino acid mixtures to create
a series of 11 batches of thermal proteins. The mxtures ranged from high
proportions of dicarboxylic amino acids to a high proportion of lysine. One
mixture consisted of an equal proportion of all amino acids tested
(asparagine and glutamine were not used), so that the amount of glycine or
each trifunctional amino acid was approximately 5.5%. Since the reference to
"extra-large portions" usually refers to the fact that -- for example --
aspartate and glutamate each are 40% while the remaining amino acids are each
1.25% (a 2:2:1 mixture), or aspartate and glutamate are each 28.5% while the
remaining amino acids are each 2.67% (a 2:2:3 mixture), or aspartate and
glutamate are each 33.3% while the remaining amino acids are each 2.1% (a
1:1:1 mixture), a mixture in which aspartate and glutamate are each 5.5%
while the remaining amino acids are each 5.5% can no longer be said to
contain "extra-large portions" of either glycine or any of the trifunctional
amino acids. (Mixture ratios refer to parts -- usually masses -- of each
major constituent, so a 2:2:3 mixture would be 2 grams aspartate, 2 grams
glutamate and 3 grams equal mixture of remaining amino acids.) As such, at
the very least one can get copolymerization even when the amount of
dicarboxylic amino acids are as low as 5% each.
> Is there a review article which summarizes
> the various mixtures of amino acids that have been tried and
> the results?
Unfortunately no. However, so far no mixture that has contained at least one
of the four polymerizing amino acids has failed to produce thermal proteins.
> 2) Has anyone tried the following experiment: (a) mix amino acids
> with sea water (b) evaporate water (c) perform Fox's experiment
> on what's left?
To may knowledge, no, but I would not anticipate that salt would be a
problem. The theoretical reason is that salt is largely insoluble in the
amino acid melt. However, that is a point that should be tested.
> 3) I guess this question is aimed mainly at geologists. What are
> the oldest salt beds? In particular, are there any that were
> laid down 3.5 - 4.0 billion years ago? If so, does the salt
> contain any (a) proteinoid microspheres, (b) amino acids,
> (c) any abiotic carbon at all?
That would be very interesting, if any such salt beds are ever found. For
now, however, there are microfossils in the 3.1 billion year old chert of the
Fig Tree Series near Baberton, South Africa, that strongly resemble
protocells, though Fox cautions the resemblence may be superficial.
Kevin L. O'Brien