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Proteinoids, or thermal proteins, are protein-like, often cross-linked molecules formed abiotically from . (1977). 9780716701637, W. H. Freeman & Co Ltd. ISBN 9780716701637 Sidney W. Fox initially proposed that they may have been precursors to the first life cells (protocell). The term was also used in the 1960s to describe peptides that are shorter than twenty amino acids found in hydrolysed protein, but this term is no longer commonly used.
When present in certain concentrations in aqueous solutions, proteinoids form small microspheres. This is because some of the amino acids incorporated into proteinoid chains are more hydrophobicity than others, and so proteinoids cluster together like droplets of oil in water. These structures exhibit a few characteristics of living cells:
Fox thought that the microspheres may have provided a cell compartment within which organic molecules could have become concentrated and protected from the outside environment during the process of chemical evolution.
Proteinoid microspheres are today being considered for use in pharmaceuticals, providing microscopic biodegradable capsules in which to package and deliver oral drugs.
In another experiment using a similar method to set suitable conditions for life to form, Fox collected volcanic material from a cinder cone in Hawaii. He discovered that the temperature was over just beneath the surface of the cinder cone, and suggested that this might have been the environment in which life was created—molecules could have formed and then been washed through the loose volcanic ash and into the sea. He placed lumps of lava over amino acids derived from methane, ammonia and water, sterilized all materials, and baked the lava over the amino acids for a few hours in a glass oven. A brown, sticky substance formed over the surface and when the lava was drenched in sterilized water a thick, brown liquid leached out. It turned out that the amino acids had combined to form proteinoids, and the proteinoids had combined to form small spheres. Fox called these "microspheres". His protobionts were not cells, although they formed clumps and chains reminiscent of bacteria. Based upon such experiments, Colin Pittendrigh stated in December 1967 that "laboratories will be creating a living cell within ten years," a remark that reflected the typical contemporary levels of ignorance of the complexity of cell structures.
Although their role as an evolutionary precursor has been superseded, the hypothesis was a catalyst to further investigate other mechanisms that could have brought about abiogenesis, such as the RNA world, PAH world, Iron–sulfur world, and protocell hypotheses.
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