The first problem beyond the stage of Haldane soup
is imagining how protein polymers could form in dilute aqueous solution,
when polymerization is a dehydration, or water-removing, process.
Equilibrium strongly favors cleavage, not polymerization.
Sidney Fox has found that dry amino acids, heated
to 160-210°C, will form polymers of molecular weights up to
300,000, provided that aspartic and glutamic acids are included
in the mixture.
The sequences of these "thermal proteinoids"
are not completely random, but show some internal order. These polymers
display a limited catalytic activity, probably resulting from their
charged side chains of acidic and basic amino acids. They catalyze
the decomposition of glucose reasonably well.
It is important not to read too much into this catalytic
activity, since even protons and platinum atoms are catalysts. It
would be surprising if a polymer with such a mixture of side chains
was not catalytic for some reaction. However, some such weakly catalytic
polypeptides, with or without metal ions, probably were the ancestors
of the much more efficient and selective enzyme catalysts of today.
These thermal proteinoids have another interesting
property. If a hot proteinoid mixture is washed with water or salt
solution, microspheres of a fairly uniform 20,000-Å diameter
are formed, as in the photograph to the right.
These are small globules of proteinoid polymer solution,
enclosed by a semipermeable proteinoid film with some of the physical
properties of simple cell membranes.
Microspheres shrink and swell in salt solutions of
different concentrations. They will grow at the expense of dissolved
proteinoid material, and have been observed to bud like yeast cells
to produce "daughter" microspheres. They can be induced
to fission by MgCl2 or by a pH change.
The enclosing film is a double layer resembling those found in soap
films and artificial and natural membranes.