BioSystems 59 2001 61 – 69
Continuous growth of autocatalytic sets
Shigenobu Mitsuzawa
a,b,
, Sei-ichiro Watanabe
a
a
Department of Earth and Planetary Sciences, Graduate School of Science, Nagoya Uni6ersity, Furo-cho, Chigusa, Nagoya, Aichi
464
-
8602
, Japan
b
TheoreticalComputational Physics Group, National Laboratory for High Energy Physics KEK
,
1
-
1
Oho, Tsukuba, Ibaraki
305
-
0801
, Japan Received 30 August 2000; received in revised form 4 December 2000; accepted 8 December 2000
Abstract
We investigated a topology of the reaction network for polymerization of amino acids as the emergence and the continuous growth of autocatalytic sets. Reaction networks including transpeptidation reaction can yield newer and
longer peptides with time having higher concentrations. Conditions necessary for the occurrence of transpeptidation can be met in actual amino acidpeptide systems. © 2001 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Origin of life; Polymerization of amino acids; Transpeptidation www.elsevier.comlocatebiosystems
1. Introduction
One of the fundamental questions regarding the origin of life is about which came first, either
proteins or nucleic acids. The view that nucleic acids,
probably RNA,
were the
primordial molecules of life Eigen et al., 1981 has been
favored by many researchers, but has not been substantiated as yet Miller, 1992. On the other
hand, some researchers have suggested the view that metabolisms of peptides could have origi-
nated prior to or independently of the replication of nucleic acids Dyson, 1985; Kauffman, 1993.
This view is based upon the vantage point that peptides could be synthesized more easily than
nucleic acids in abiotic conditions. Ito et al. 1990 suggested that polypeptides carrying molecular
weights of 1000 – 4000 Da had secondary struc- tures and catalytic functions for many metabolic
reactions. Seffens 1995 investigated the possibil- ity that peptide systems might have exhibited
metabolic and replicative activities. Recently, re- action networks of self- and cross-replicating pep-
tides consisting of about 30 residues have been constructed in the laboratory by Lee et al. 1996
and other researchersLee et al., 1997; Yao et al., 1998. These observations strongly support the
possibility of peptide systems of abiotic origin.
In order to have functional peptide systems, a set of long peptide chains must be prepared abiot-
ically. In this study, we investigate how longer peptide chains could be synthesized from amino
Corresponding author. Tel.: + 81-298-796102; fax: + 81- 298-645755.
E-mail address
:
shigenobu.mitsuzawakek.jp S.
Mit- suzawa.
0303-264701 - see front matter © 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 3 0 3 - 2 6 4 7 0 0 0 0 1 4 5 - 3
acids that may be long enough to carry primitive metabolic capabilities.
Kauffman 1986 proposed an autocatalytic set of polymers. Simulation studies of autocatalytic
sets Bagley and Farmer, 1991, however, revealed that it is not possible to synthesize longer poly-
mers with high concentrations unless the equi- librium constant of condensation is large enough.
In the present study, we performed numerical experiments by varying the topology of reaction
networks. Our major finding is that even if the equilibrium constant of condensation is small,
certain reaction networks can synthesize many kinds
of longer
polymers with
higher concentrations.
2. Numerical model
