Editing Proteinoid

{{Refimprove|date=December 2009}}
'''Proteinoids''', or '''thermal proteins''', are [[protein]]-like, often cross-linked molecules formed abiotically from [[amino acid]]s.<ref name='Fox 1997'>{{cite book | vauthors = Fox SW, Klaus D |author-link1=Sidney_W._Fox |title=Molecular Evolution and the Origin of Life |year=1977 |publisher=W. H. Freeman & Co Ltd |isbn=978-0-7167-0163-7 }}</ref> [[Sidney W. Fox]] initially proposed that they may have been precursors to the first [[life|living]] [[cell (biology)|cells]] ([[protocell|protocells]]).<ref name="Fox 1997" /> The term was also used in the 1960s to describe peptides that are shorter than twenty amino acids found in hydrolysed protein,<ref>{{cite journal | vauthors = Hayakawa T, Windsor CR, Fox SW | title = Copolymerization of the Leuchs anhydrides of the eighteen amino acids common to protein | journal = Archives of Biochemistry and Biophysics | volume = 118 | issue = 2 | pages = 265–272 | date = February 1967 | pmid = 6033704 | doi = 10.1016/0003-9861(67)90347-5 | hdl-access = free | hdl = 2060/19660025877 }}</ref> but this term is no longer commonly used.<ref name="Fox 1997" />

==History==

In trying to uncover the intermediate stages of [[abiogenesis]], scientist [[Sidney W. Fox]] in the 1950s and 1960s, studied the spontaneous formation of [[peptide]] structures under conditions that might plausibly have existed early in Earth's history.<ref name="hazen">{{Cite book |last=Hazen |first=Robert M. |title=Genesis: the scientific quest for life's origin |date=2005 |publisher=Joseph Henry Press |isbn=978-0-309-09432-0 |location=Washington, DC}}</ref>{{rp|199-201}} He demonstrated that [[amino acid]]s could spontaneously form small chains called peptides. In one of his experiments, he allowed amino acids to dry out as if puddled in a warm, dry spot in prebiotic conditions. He found that, as they dried, the amino acids formed long, often cross-linked, thread-like microscopic [[polypeptide]] globules, he named "proteinoid microspheres".<ref name="foxexp">{{cite web | title=Origins of life | vauthors = Walsh B | publisher=University of Arizona | at=Part 4: Experimental studies of the origins of life | date=January 13, 2008 | url=http://nitro.biosci.arizona.edu/courses/EEB105/lectures/Origins_of_Life/origins.html | archive-url=https://web.archive.org/web/20080113152408/http://nitro.biosci.arizona.edu/courses/EEB105/lectures/Origins_of_Life/origins.html | archive-date=January 13, 2008 | url-status=dead | access-date=April 7, 2019 }}</ref>

==Polymerization==
The abiotic [[polymerization]] of amino acids into proteins through the formation of [[peptide bond]]s was thought to occur only at temperatures over 140&nbsp;°C. However, the biochemist Sidney Walter Fox and his co-workers discovered that [[phosphoric acid]] acted as a [[catalyst]] for this reaction.{{Citation needed|date=March 2014}} They were able to form protein-like chains from a mixture of 18 common amino acids at 70&nbsp;°C in the presence of phosphoric acid, and dubbed these protein-like chains proteinoids. Fox later found naturally occurring proteinoids similar to those he had created in his laboratory in lava and cinders from [[Hawaii]]an [[volcano|volcanic]] vents and determined that the amino acids present polymerized due to the heat of escaping gases and lava.{{Citation needed|date=March 2014}} Other catalysts have since been found; one of them, amidinium carbodiimide, is formed in primitive Earth experiments and is effective in dilute [[water|aqueous]] solutions.

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|hydrophobic]] than others, and so proteinoids cluster together like droplets of oil in water. These structures exhibit a few characteristics of living cells:

#An outer wall.
#Osmotic swelling and shrinking.
#Budding.
#Binary fission (dividing into two daughter microspheres).<ref>{{cite book| vauthors = Fox SW, Klaus D |title=Molecular Evolution and the Origin of Life |edition= Revised |year=1977|publisher=Marcel Dekker|location=New York | veditors = Fox JL |isbn= 978-0-8247-6619-1 }}</ref>
#Streaming movement of internal particles.<ref>{{Cite web |title=There are two basic ideas about how life on Earth originated |url=https://sbpoley.home.xs4all.nl/abiog/virginiaorigin.htm |access-date=2025-05-11 |website=sbpoley.home.xs4all.nl}}</ref>

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 [[molecular evolution|chemical evolution]].<ref name='Fox 1997'/>

Proteinoid microspheres are today being considered for use in pharmaceuticals, providing microscopic biodegradable capsules in which to package and deliver oral drugs.<ref>{{cite patent |country=US |number=5601846 |gdate=1997-02-11 |status=expired |inventor = Milstein SJ, Kantor ML |assign=Emisphere Technologies Inc  |title=Proteinoid microspheres and methods for preparation and use thereof}} </ref>

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 {{convert|100|C}} just {{convert|4|in}} 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.{{Citation needed|date=March 2014}} 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.<ref>{{cite book |title= Our amazing world of Nature: its marvels & mysteries |url= https://books.google.com/books?id=wPNPAAAAYAAJ&q=%22Colin+S.+Pittendrigh%22,+%22laboratories+will+be+creating+a+living+cell+within+ten+years%22 |year=1969 |publisher=Reader's Digest Association |isbn=978-0-340-13000-1 |page=287 |oclc=7993251 }}</ref>

==Legacy==

Fox has likened the amino acid globules to cells, and proposed it bridged the macromolecule to cell transition. However, his hypothesis was later dismissed as proteinoids are not [[proteins]], they feature mostly non-[[peptide bond]]s and amino acid [[cross-link]]ages not present in living organisms. Furthermore, they have no compartmentalization and there is no information content in the molecules.

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]],<ref name="hazen" />{{rp|201}} such as the [[RNA world]], [[PAH world hypothesis|PAH world]], [[Iron–sulfur world theory|Iron–sulfur world]], and [[protocell]] hypotheses.{{Cn|date=September 2017}}

==See also ==

*[[Abiogenesis]]
*[[Jeewanu]]
*[[Protocell]]
*[[Proto-mitochondrion]]

== References ==
{{Reflist}}

== Further reading ==
{{refbegin}}
* {{cite journal | vauthors = Fox SW, Harada K | title = Thermal copolymerization of amino acids to a product resembling protein | journal = Science | volume = 128 | issue = 3333 | pages = 1214 | date = November 1958 | pmid = 13592311 | doi = 10.1126/science.128.3333.1214 | series = New Series | bibcode = 1958Sci...128.1214F | jstor = 1756313 }}
* {{cite journal | vauthors = Matsuo M, Kurihara K | title = Proliferating coacervate droplets as the missing link between chemistry and biology in the origins of life | journal = Nature Communications | volume = 12 | issue = 1 | pages = 5487 | date = September 2021 | pmid = 34561428 | pmc = 8463549 | doi = 10.1038/s41467-021-25530-6 }}
* {{cite journal | vauthors = Pappelis A, Fox SW | title = Domain Protolife: Protocells and metaprotocells within thermal protein matrices. | journal = Journal of Biological Physics | date = March 1995 | volume = 20 | issue = 1-4 | pages = 129-132 | doi = 10.1007/BF00700429 }}
{{refend}}

{{Self-replicating organic structures}}
{{Organisms et al.}}
[[Category:Origin of life]]