Even more interesting are coacervates prepared with enzymes inside.
These can absorb substrate molecules from solution, catalyze chemical
reactions, and let the products diffuse out.
If coacervates containing the enzyme phosphorylase are prepared,
and glucose-1-phosphate is added to the bulk solution, the primed
glucose molecules will diffuse into the coacervate droplets and
be polymerized there into a starch polymer.
If the coacervates also contain the enzyme amylase, then the starch
produced by the first enzyme is chopped back to disaccharide molecules
of maltose, which diffuse into the bulk solution again. Coacervates
with these two enzymes are miniature factories for turning glucose-1-phosphate
into maltose, using the energy of the phosphate bond in the starting
In another experiment, coacervates were prepared that contained
mitochondrial NADH dehydrogenase, the flavoprotein enzyme found
at the beginning of the respiratory chain. These droplets could
absorb NADH and a reducible dye from the solution, reduce the dye
molecules, and release dye and NAD+ back into solution.
In the most spectacular model experiment of all, coacervate drops
containing chlorophyll were allowed to absorb ascorbic acid and
an oxidized dye that could not be reduced spontaneously by ascorbate
When the droplets were kept in the dark, nothing happened; but
when they were illuminated by light the dye became reduced. In a
very close parallel to the single-center photosynthesis of bacteria,
chlorophyll molecules absorbed light energy, and used their excited
electrons to reduce the dye molecules.
Ascorbate merely played the role of H2S
in the electron-transfer chain by providing the electrons required
to restore the electron deficit in the chlorophyll molecules. Reduction
occurred with a net increase in free energy, the increased energy
coming from the absorbed light.