Duane L. Rohlfing

Coacervate-like microspheres from lysine-rich proteinoid

Microspheres form isothermally from lysine-rich proteinoid when the ionic strength of the solution is increased with NaCl or other salts. Studies with different monovalent anions and with polymers of different amino acid composition indicate that charge neutralization and hydrophobic bonding contribute to microsphere formation. The particles also form in sea water, especially if heated or made slightly alkaline. The microspheres differ from those made from acidic proteinoid but resemble coacervate dtoplets in some ways (isothermal formation, limited stability, stabilization by quinone, uptake of dyes). Because the constituent lysine-rich proteinoid is of simulated prebiotic origin, the study is interpreted to add emphasis to and suggest an evolutionary continuity for coacervation phenomena.

Polyamino Acids: Preparation from Reported Proportions of "Prebiotic" and Extraterrestrial Amino Acids

Polyamino acids were thermally prepared from the proportions of amino acids identified (sometimes after hydrolysis) among the products of simulated prebiotic syntheses and (after hydrolysis) in lunar and meteoritic samples. Inferences are made concerning the composition of prebiotic protein and the possible extraterrestrial existence of protein-like polymers.

Evolutionary processes possibly limiting the kinds of amino acids in protein to twenty: a review.

Abstract Only 20 of more than 250 biosynthetic amino acids are common (coded) constituents of contemporary protein. In this paper, several stages of evolution, both prebiotic and biotic, are examined for means by which other (non-proteinous) amino acids may have been selected against. Simulated prebiotic experiments indicate that some non-proteinous amino acids were present prebiotically, that they could be incorporated during the formation of prebiotic protein, and that they would function in such protein. Biotic selection is thus indicated. Non-proteinous amino acids currently are available via biosynthetic pathways for potential incorporation into bioprotein. Codon-anticodon interaction, peptidyl transferases, and elongation and termination factors of protein synthesis do not show the specificity needed to preclude non-proteinous amino acids. Highly specific recognition among amino acids, tRNAs, and activating enzymes is concluded to be why the kinds of amino acids in contemporary protein are limited to twenty. Some of several theories concerning the origin, nature and evolution of the genetic code can readily accommodate non-proteinous amino acids. Some evidence suggests that such amino acids were eventually eliminated from protein because they were less suitable than related proteinous amino acids. However, deterministic or “direct interaction” theories currently lack sufficient experimental support to answer how non-proteinous amino acids were precluded; such theories, being testable, probably have the most potential for providing an answer.

Thermal polymerization of amino acids under various atmospheres or at low pressures.

The kinds and proportions of amino acids formed in two simulated prebiotic experiments or detected in hydrolyzed extracts of three extraterrestrial samples were found to polymerize thermally under various atmospheres or at low pressures. Yields, tested properties, and amino acid compositions of the polymers were not influenced by the type of enveloping atmosphere, including two simulated prebiotic atmospheres and five pure gases. However, polyamino acids prepared at low pressure (0.02, 10(-4) atm) were obtained in appreciably greater yield than those synthesized at 1 atm; amino acid composition was somewhat influenced by low pressure. The results indicate that polyamino acids could have been formed thermally under a variety of possible prebiotic atmospheres and on planetary bodies of low atmospheric pressure.

Formation of proteinoid microspheres under simulated prebiotic atmospheres and individual gases

The formation of microspheres from acidic and basic proteinoids was attempted under simulated prebiotic atmospheres and constituent gases thereof. Both types of proteinoid yielded microspheres under carbon dioxide, carbon monoxide, methane, hydrogen sulfide, hydrogen, nitrogen, and oxygen (tested separately) and also under nitrogen-carbon dioxide atmospheres; higher proportions of carbon dioxide resulted in fewer spheres from basic proteinoid. Neither type of proteinoid formed spheres on 10-minute exposure to ammonia or methane-hydrogen-ammonia atmospheres. (Brief exposure resulted in spheres from basic proteinoid.) The effects, both qualitative and quantitative, were indicated by control experiments to be due to pH, rather than to the specific gas (or ion). The results suggest that the proteinoid microsphere model for protocells is applicable under a variety of possible prebiotic atmospheres, with some restrictions imposed by pH.

Catalytic activities of thermally prepared poly-alpha-amino acids - Effect of aging

Thermally prepared poly-α-amino acids were tested after being stored in the dry state for 5 to 10 years. Polymers effective in catalyzing the hydrolysis of p-nitrophenyl acetate showed the same levels of activity as observed 10 years earlier. Polymers effective in catalyzing the decarboxylation of oxaloacetic acid had in 5 years become insoluble in assay medium; their activity, however, had increased by 32 to 145 percent. The results suggest that particular primitive enzyme molecules could have been stable enough to have contributed to evolutionary processes long after they had been produced.

The Development of the Proteinoid Model for the Origin of Life

It is a pleasure to contribute an article commemorating seven full decades of Sidney W. Fox and two-and-a-half decades of the proteinoid theory. This article in part reviews some of Fox’s major research accomplishments, which have evolved to be known as the proteinoid model (or theory) for the origin of life. However, the range of his research and of his thinking are, I believe, better viewed after some focus on features of the unique arena in which the work is being done, and on some preconceptions and untested speculations that abound in that arena. Also, some ideas about the significances and the acceptance of the proteinoid model are presented.

Inclusion of nonproteinous amino acids in thermally prepared models for prebiotic protein

Abstract Sixteen nonproteinous amino acids (those not coded for in contemporary protein biosynthesis) were incorporated during the thermal formation of polyamino acids under postulated prebiotic conditions, although not all into a single polyamino acid. The copresence of proteinous or even α-amino acids was not required. (Norleucine color equivalents and elution times on a Beckman model 120C amino acid analyzer were determined for these nonproteinous amino acids). The results suggest that prebiotically available nonproteinous amino acids would have been constituents of prebiotic protein if the latter were formed thermally. Some differences in properties of the polyamino acids could be attributed to particular nonproteinous amino acid residues; however, the tested properties did not suggest a means for evolutionary selection against nonproteinous amino acids as a group . Selection against this class of amino acids in toto was likely a later, biotic, event.

Stereo-Enriched Poly-α-Amino Acids: Synthesis Under Postulated Prebiotic Conditions

In 1954, Fox and Middlebrook reported (1) that some amino acids common to protein copolymerize thermally, under simulated prebiotic conditions. Many subsequent studies (reviewed in references 2 and 3) have extended the thermal method to produce oligo- or hetero-tonic (4) polyamino acids [termed proteinoid when some of each of the proteinous (5) amino acids are incorporated]. The thermal polymers exhibit many properties in common with present-day protein, including molecular weight range, catalytic activity, non-randomness, selective associations, and morphogenecity. They are regarded as models for prebiotic protein (2 – 4).

Evolution of Models for Evolution

Of the many accomplishments of Professor Oparin, two are outstanding. His experimental investigations with coacervate droplets, designed and interpreted in the context of the origin of life, have provided much insight into the origins and evolution of protocells. Of even greater overall impact is his pioneering hypothesis concerning the origin of life that suggested conditions, chemical species, and processes of prebiotic evolution. He has presented us with a theoretical model for molecular and cellular evolution.