By Sean Henahan, Access Excellence
In a simulation of the days when the Earth was
covered in primordial ooze, researchers at the University of
California, San Diego have synthesized pantetheine, an ingredient
considered essential for the development of life on the planet.
The nature of the origin of life remains one of the most
intriguing questions in biology. Researchers at the University of
California, San Diego's Specialized Center of Research and
Training in Exobiology are approaching the question by simulating
environmental conditions as they are thought to have existed in
"prebiotic" times. The researchers are studying the abiotic
synthesis of biomolecules to determine which ones could have been
present on Earth before life arose and, thus, may have been
important to the first living organisms.
The UCSD research team is led by Dr. Stanley Miller. Dr.
Miller is well known for his 'primordial soup' experiment
conducted in 1953. At that time he demonstrated that amino acids
could be formed by passing an electric current through a flask
of methane. This suggested that life could have arisen from
materials and conditions present in early Earth history.
Dr. Miller believes many other chemicals in addition to
amino acids would have to have been present to facilitate the
transition to living organisms. In particular, the presence of
pantetheine could have enhanced the transition process.
Pantetheine is related to coenzyme A, an essential component for
protein formation. Coenzyme A is used by every known organism to
assist in a wide variety of chemical reactions and it is possible
that in the very earliest organisms this role was played by
pantetheine alone, notes Miller.
In their recent experiment, the UCSD scientists heated a
mixture of pantoyl lactone, beta-
alanine and cysteamine at 40 degrees C (105 degrees F). All three
chemicals are believed to have been present on the early Earth.
Among the other chemicals formed was pantetheine. This suggests
pantetheine could have been created at the margins of evaporating
pools of water in prebiotic times.
"These components are extremely soluble and so would have
been preferentially concentrated in evaporating bodies of water,
for example on beaches and at lagoon margins. Our results show
that amide bonds can be formed at temperatures as low as 40
degrees C, and provide circumstantial support for the suggestion
that pantetheine and coenzyme A were important in the earliest
metabolic systems," noted Miller.
There are two main hypotheses regarding the prebiotic
synthesis of coenzymes. One, the "RNA world" hypothesis, holds
that coenzymes were part of the covalent structure of RNA, and
assisted in the RNA-based metabolism. Another hypothesis suggests
that the RNA world was preceded by a thioester world. According
to that hypothesis, coenzyme A played an essential role in the
activation of amino acids and hydroxy acids in peptide synthesis.
The research provides evidence for the presence of an
important ingredient in the original soup of life. It has been
demonstrated that amino acids can form abiotically in a number of
ways and are used by modern organisms for the manufacture of
proteins. Sugars, however, which are components of modern genetic
materials such as DNA or RNA are thought to be too unstable to
have been widespread on Earth before life arose. Another of the
remaining "big questions" is how and when did non-living
molecules turn into life forms and begin to make copies of
The current research appeared in the Feb. 23 issue of the
journal Nature (v.373, Miller et al.).
Transmitted: 95-03-20 19:34:24 EST