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Evolution of the biosynthesis of the branched-chain amino acidsThe origins of the biosynthetic pathways for the branched-chain amino acids cannot be understood in terms of the backwards development of the present acetolactate pathway because it contains unstable intermediates. We propose that the first biosynthesis of the branched-chain amino acids was by the reductive carboxylation of short branched chain fatty acids giving keto acids which were then transaminated. Similar reaction sequences mediated by nonspecific enzymes would produce serine and threomine from the abundant prebiotic compounds glycolic and lactic acids. The aromatic amino acids may also have first been synthesized in this way, e.g. tryptophan from indole acetic acid. The next step would have been the biosynthesis of leucine from alpha-ketoisovalerc acid. The acetolactate pathway developed subsequently. The first version of the Krebs cycle, which was used for amino acid biosynthesis, would have been assembled by making use fo the reductive carboxylation and leucine biosynthesis enzymes, and completed with the development of a single new enzyme, succinate dehydrogenase. This evolutionary scheme suggests that there may be limitations to inferring the origins of metabolism by a simple back extrapolation of current pathways.
Document ID
19950057134
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Keefe, Anthony D.
(University of California, San Diego, La Jolla, CA US, United States)
Lazcano, Antonio
(UNAM Mexico)
Miller, Stanley L.
(University of California, San Diego, La Jolla, CA US, United States)
Date Acquired
August 16, 2013
Publication Date
June 1, 1995
Publication Information
Publication: Origins of Life and Evolution of the Biosphere
Volume: 25
Issue: 1-3
ISSN: 0169-6149
Subject Category
Life Sciences (General)
Accession Number
95A88733
Distribution Limits
Public
Copyright
Other

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