NO HOMOCHIRALITY – NO LIFE
Akihiko Shimada
Sustainable Environmental Studies, Graduate School of Life and Environmental Sciences, Universityof Tsukuba, Tsukuba, Ibaraki 305-8572, Japanashimada@envr.tsukuba.ac.jp
Abstract
Life is made up from biomolecules with
one-handed structure. L-dominant exclusive choiceof enantiomeric type in optical amino acid isomers
raises important issues concerning life science. This
report discusses why it is essential for life to be madeup of homochiral molecule. A mechanism that selects
homochiralmolecules
lies
inenzymestereoselectivity, and therefore the studying of it will
be important to solve a problem on origin of life andan enigma of life’s birth. This report concludes there
is no life without homochirality.
(Keywords)
Origin of homochirality, Enzyme enantioselectivity,
High level of organization, Kaname-isi,No homochirality – no life
１ ． Importance of optical isomeric form inbiomolecules
A life body can be classified into organ, tissue
and cell according to size. Further segmentation
comes to the macroscopic structures from subcellularorganelle as cell membrane, nucleus or mitochondria
to microstructural body as ribosome or microtubule.
Additional fragmentation only ends in a subdivisionof biomacromolecule. We can thus say that life is ahighly organized macromolecular assembly. Protein
and nucleic acid of biogenic macromolecules are themost important. Protein or nucleic acid is produced
through dehydrated polycondensation reaction
between L-amino acids or nucleotides. Theirbiomolecules provide ultraprecise stereostructure. For
example, enzyme protein consists of one or more
protein chains. A protein chain will be in the range of
50 to 2000 amino acid residues, giving primaryamino acid sequence, and even secondary structure as
right-handed α- helix and/or β-pleated sheet thatare connected to each other through hydrogenbonding occurring between NH and CO groups in the
chain (Fig. 1). A single protein chain may containmultiple secondary structures. In addition tohydrogen bond, other interactions between the side
chains of amino acids such as ionic interactions, vander Waals dispersion forces and sulphur bridges foldinto higher stereostructure to exhibit a catalytic
activity. The elaborate stereostructure of enzyme
conducts the catalytic reaction with substrate.
However, if there is the slightest change in thestereostructure, the enzyme cannot immediately reactwith the substrate. Transient fluctuation ofenvironment surrounding enzyme, for example, pHof aqueous solution, changes its surface charge state
to cause a small change of the stereostructure andthen lead to a decrease in the enzyme activity. Thus
there is the most optimal environment in enzyme

Viva Origino 40 (2012) 40 - 46
© 2012 by SSOEL Japan

Fig. 1 Right-handed α - helix and β -pleated sheet
structures formed by poly-L-peptide

reaction, in which enzyme provides stereospecificity
together with substrate specificity. As a result protein
is made up from L-amino acids, leading to havehomochiral structure. On the other hand,
deoxyribonucleic acid (DNA) has antiparallel
right-handed double helical structure, which showsconsequences in base- pairing and base- stacking byhydrogen bonds that occur between complementary
nucleotide base pairs, that is, cytosine-guanine andadenine-thymine. L-amino acid and D-deoxyribose(Fig. 2) are essentially responsible for theright-handed helical structure of protein and DNA.
The homochirality in an optical isomeric type ofamino acid or sugar, which is used as parts in

Fig. 2 Stereochemical structure of alanine and deoxyribose40Viva Origino 40 (2012) 40 - 46

building this spiral structure, is absolutely required.
It is enzyme stereospecificity that could makedifferential activity between enantiomeric substratemolecules. The most conspicuous instance of it is apharmacological effect of thalidomide (Fig. 3).
Thalidomide has R type and S type in opticalisomeric type because it has a chiral carbon. While
the R type has a positive effect of sedative activity,
the S type teratogenesis that causes phocomelia, quite
the contrary and enormous negative property ascompared with the R type. A single mistake thatmarketed this racemate later brought about a terrible
tragedy. (The later research indicated the R type wasracemated into the S type in body.) [1] We can havean immediate experience with the difference between
physiological actions on DL-enantiomeric aminoacids. All foods include free amino acids. Examplesof free amino acid – rich foods include seaweed highin gulutamic acid, aspartic acid and proline, histidine
high in fish and dried bonito, or alanine, glycine,
serine and proline high in crab, squid and sea urchin.
As every amino acid has its own taste, food withspecial flavor can be created by combining one ormore amino acids. [2] For L type of human essential
amino acids (threonine, methionine, leucine, valine,
isoleucine, phenylalanine, lysine and tryptophan), wenote a bitter taste in the mouth except sweet threonine.
Generally speaking, non-essential amino acids havesweet or umami. For example, L-gulutamate has
umami along with sour. The taste of amino acid isdifferent between enantiomeric type, too. It is nicefor practical experiment to lick both D and L types of
19 biological amino acids in addition to glycine withyour tongue. Glycine without chiral carbon has thesimplest structure of them, but is sweet just as its
name suggests. While L-valine and L-leucine have
bitter taste, their D type has sweetness. In aromatic
amino acids such as phenylalanine, thyrosine andtryptophan, L type is bitter or tasteless, but D typegenerally has very strong sweet taste. Surprisingly,
D-tryptophan is particularly thirty five times sweeter
than sucrose. D type is sweet but L type bitter inother neutral α-amino acids, except D-methionine istasteless. In imino amino acids as proline as well asacidic amino acids, L type is sweet but D type isalmost tasteless. Acidic L-amino acids also has
umami, and so used as seasoning. Interestingly,
D-aspartic
acid
has
no
umami,but
β-amido-D-aspartic acid is sweet such as neutralamino acids. Amino acids thus have umami, sweet or
acerbity according to their stereostructures.
As an aside, there is said to be interspecies
difference in sweet sensitivity. For aspartame as an
artificial sweetener or stevia, Stevia rebaudiana plantleaves known as a South American herb that has beenused as a sweetener by the Guarani Indians ofParaguay for hundreds of years with a delicious andrefreshing taste that can be 30 times sweeter thansugar, human and monkey can sense a strong sweet
taste, but rat cannot sense it. For monellin, a sweet
protein which was discovered in 1969 in the fruit of
the West African shrub known as serendipity berry(Dioscoreophyllum cumminsii) and can elicit a flavor

Fig. 3 Thalidomide. *C is a chiral carbon.

approximately 100,000 times sweeter than sugar, oldworld monkey as crab-eating monkey can sensesweet, but new world monkey cannot.
Five tastes of salty, sour, bitter and umami inaddition to sweet are determined by a high or low
affinity of a molecule for a species-specific gustatory
receptor. Their relation can be just explained byhost-guest interaction, that is, three point interaction
theory. D and L type in a mirror image relationshiphave the difference in spatial configuration amongresidues bonding with chiral carbon, and therefore
the antipodes make a difference in affinity withgustatory receptor to allow us to perceive different
tastes. This indicates the receptor structure itself on
the surface of gustatory cell on our tongue is chiralmoiety and consequently, provides different
interactions between L and D type. As shown in Fig.
4, in four L-amino acid side chains put as A, B, C, D,
and D-amino acid side chains as A, B, C′, D, whenA, B and C residues of L-amino acid respectively
bind with α, β, and γ sites on the receptor surface toproduce a taste sense. Any gustation doesn’t occurs
or entirely-different one is given in D-amino acid.
Since Pasteur’s discovery that yeast ferments to use
d-tartrate all up but cannot ferment l-tartrate [3],Van’t Hoff and Le Bell independently developed thetetrahedral structural theory of carbon [4]. Although
the three point interaction theory has not yet been
perfected, many researchers have applied it tounderstand a mechanism of enzyme stereospecificity.
When we study the physiological activity of
biology-related substances, we cannot neglect
problems on enantioselectivity since the thalidomide
case. Optical resolution technology holds great
promise for the future to elucidate the mechanism of
the enantioselectivity.

Fig. 4 Binding site with L- and D-amino acid side chainsand gustation receptors

41

Viva Origino 40 (2012) 40 - 46

As described above, the biological importanceof enantiomeric type can be sufficiently understood.
Physiological difference on enantiomers reflects thatlife is made up from biomolecules with one-handed
structure. In other words, life itself can be said to behomochiral existence. Here two questions will
naturally occur. One is why life must be made up of
homochiral molecule, and the other is why aminoacids and sugars as biochiral molecules must be L
type and D-type, respectively. We discuss on these
problems in the below some chapters.

and 19 amino acids with chiral carbon), its
combination is (20+19)100=39100~10160, astronomical
number! If an enantiomeric type of these amino acids
is either L or D, its combination is 20100~10131. This
combination number decreased to 10-29-fold of theformer to give drastic decrease. As understood fromthis result, when we artificially synthesize
L-polypeptide from 100 amino acids, we will use
only L type instead of racemate to synthesize. Early
life might also have taken the same strategy.
In the past time, Pasteur thought there wassomething like symmetry-breaking pressure in space.
Today, it is not believed but no one could deny theconcept of matters’ automotility to higherorganization, or evolving matters. Various subnuclear
particles are born, repeating constant alignment andrealignment in this universe to produce atoms andsubsequently elements. Once again, different
elements mutually repeat the meeting and parting toyield molecules, whose movement conducts to form
organic molecules, and proceeds to chemical
evolution possible, and ultimately connects to thebirth of life. Matters born in this universe can evolveto obtain new property and function by raising a levelof their own organization under natural pressure.
Matters will be destined to organize to higher level inthis universe. The most highest organized mattersystem was born in early earth about forty billion
years ago. This ultimate highly-organized system waslife, a living matter system with dynamically
self-preserving and self-propagating property. Of
course, it goes without saying that environmental
conditions such as temperature, fluid, moisture andsustainable reductive atmosphere was furnished to
produce it. Unlike Earth, Mars environment isinsufficient to produce life. However, Mars was richin water four billion years ago. It was once abeautiful water-filled planet like Earth, but today was
all gone to pot because water evaporated 3.5 billion
years ago. Our plant has too many favorable
conditions
forlife
comparedtoMars.
Self-preservation and self-propagation are the most
biotic features of matter’s evolution. After early life
was born and obtained full adaptation to global
environment, it increased the level of the matter’s
evolution to proceed to a stage of spontaneous life
evolution, which created new life with higherorganization. Human reaches the highest state of theevolution, regarded as historical existence with thehighest precise organization as the matter’s evolutionthat the evolution of cosmic elementary particles
starts 13.7 billion years ago, and continues tochemical and biological evolution.
In this context, a key word for essential
requirement under which life is generated fromabiotic matters is matter’s highly-organization. For
example, we here think about the relationshipbetween polyamino acids or nucleic acids withhigher-order structure. L-amino acid or D-sugar canbe regarded as basic parts to assemble thesemacromolecules. As described above, uniform
enantiotype such as L-amino acid or D-sugar isnecessary to make higher organized macromolecule.

2. The necessity of homochiral molecules for birthof life
We can answer about the first problem withcomparative ease from the following two standpoints.
One lies in a synthetic efficiency of polypeptide.
L-amino acid and its antipode, D-amino acid, havethe same physicochemical properties. Now imagine a
dipeptide synthesized from two L- and/or D-aminoacids. As a dipeptide has two chiral carbons, it has
four isomers. Both L-L (dipeptide composed of two
L- amino acids; Dipeptide is henceforth expressed inthis abbreviated notation) and D-D dipeptides havethe same physicalchemistry because they are in a
mirror-image relationship to each other. The samegoes for L-D and D-L, too. However, the formergroup (L-L, D-D) and the latter one (L-D, D-L)
merely have a diastereomeric relationship withdifferent physicalchemistry. Therefore, they may beconsidered as different molecules from one another.
These relations are illustrated in Fig. 5, in which twoenantiomers are shown in continuous line and four
diastreomers in dotted line.
When a dipeptide is synthesized from aminoacids including L and/or D form, compounds withfour different enantiomeric forms are produced. As
the number of amino acid increases in a polypeptide
such as tripetide, tetrapeptide, pentapeptide---, thenumber of isomer correspondingly increases at an
exponential rate as 8, 16, 32 ---. Let's think about an
artificially-synthesized polypeptide from 100 aminoacid racemates. It has combinations of 2100, andtherefore it means that one of their polypeptides ispicked to select the only right L-polypeptide. If wethink in terms of all biological amino acids (glycine

Fig.5 	  Enantiostructural relationship of a dipeptide
composed of two L- and/or D-amino acids

42Viva Origino 40 (2012) 40 - 46

If some D-amino acids invade L-dominant aminoacid world, its stereostructure is known to become
unstable [6]. When a polyamino acid chain issynthesized from racemic amino acids mixed with L
and D form, the enantiomerically mosaic polypeptide
becomes unstable, and can neither elongate nor makea highly precise organized structure. Since life is avery highly-organized system, the first strategy is tounify an enantiotype of enantiomers as components.
However, natural world will be impossible to achieve
it. Therefore, we should think the way to highorganization from D- and L-mixtures. It is indeed
possible to make a highly organized macromoleculefrom DL-racemate. A very sophisticated mechanism
which can differentiate D-type from L-type and alsodeliver the right enantiomeric type to the right place,is necessary to produce it. It may be difficult toimagine a system, which can recognize and choose Lor D-type, is naturally generated. However, enzyme
plays the role in real life world. When did amechanism of this enzyme stereospecificity occur? Inother words, it means to ask whether the mechanism
was generated during abiotic or biotic evolution.
Although the present study cannot give this questiona clear answer, we can at least say the mechanism of
enzyme enantioselectivity might had been alreadydriven by early life because enzyme should havealready existed at its birth. We can thus think it wascompleted during abiotic period. Primitiveenvironment of early earth was probably filled with
racemic mixtures of DL-racemates, and so themechanism was absolutely essential to selectone-handed molecule and make higher organizedstructure. The emergence of the mechanism is awatershed that proceeds to biotic era from abiotic one.
The moment of its appearance become a starting
point for life evolution. It is quite right to say that life
is a highly-organized homochiral system withhomochiral structure and it cannot be constructeduntil homochiral components are supplied by themechanism of the enantioselectivity.

the following future love story. You will travel inspace to land on a planet in no distant future. Suppose
you find a living creature there, when you land on the
ground. While it has the same feature and function as
earth’s life, an optical isomeric form of amino acid is
D-type, or the opposite of earth’s enantiomer. D-life
evolves on this planet because it independently takes
separate evolutionary paths from ours. That is stating,in other words, that L-life on earth lives in L-world
and D-life on the planet in D-world. Please here
imagine what it would be like if L-earthman contacts
with D-girl on the planet. L-man fortunately meets abeautiful D-girl there. Of course, she has the samefeature, morphology and function as earthman exceptthat she is made up of D-amino acids. They will soon
fall in love at first sight. They promise to love eachother and always have such a fun time together.
Before long, they want to marry. However, reality is
cruel. It is important to note that L-man is composedof the opposite enantiomer against her. Some big
troubles occur, involved in reproduction, food andhealth. First of all, they can't have any child due toimpaired fertility problems arising from enantiomericincompatibility, though both love and newlywed life
can be shared immediately. A short time later,
another inescapable fatal problem will happen. He
must eat D-food on the planet after L-human runs outof L-foods carrying from the Earth. However, D-foodis not metabolized as nutrition. He becomes reduced
to skin and bone day by day. He will need to return tothe earth as early as possible. Consequently, theirromance will end in the result that they proceedstraight into disaster. Even if food problem is solved,
unfortunate calamity will visit. As D-bacterial
pathogen in D-world doesn’t act on L-livingorganism, D-world is like bioclean room for L-livingorganism. This means that L-organism in D-world
dies of only old age or cancer. Because, even if
D-organism suffer from killing disease, L-organism
are as fine as can be, healthy L-organism can easily
wipe out the deadly ill D-organism. The only resultthat their contact brings about will be to end indisaster. L-organism threatens the existence ofD-organism, and L-world becomes antagonistic
against D-world (Fig. 6).
As above description, L-world and D-world is
not mix at all like oil and water in the level ofhighly-organized life, while the physicochemical

3. What is the origin of homochirality?
We can adequately understand through thediscussion thus far that homochiral parts selected byenantioselectivity are necessary to make homochiralstructure, and a wide variety of sophisticatedcompilation of it is life. Therefore life itself ishomochiral. The main question that begs to be asked
is; Why was L-amino acid exclusively chosen as
biological component? Since L- and D-enantiomer
have the same physicochemical property, any
problem is nothing even if early protein selects
D-amino acid instead of L-amino acid. Neverthelesslife forces through exclusive use of L-amino acid.
There must lie some deeper ground for life’s
exclusive selection of L-amino acid, though ourpresent knowledge cannot give any answer to it.
What we can say for sure is that something bad isgoing to happen when L and D are mixed.
The above discussion has thought of molecularlevel. When discussing individual level, this is awhole different ball game. We want you to discuss

Fig.6	
  Threat of L-world against D-world on D-planet43

Viva Origino 40 (2012) 40 - 46

character of L- molecule is quite equal to that of
D-molecule at low molecule level. Although we
distinguish monomeric L- and D-amino acid in
optical rotation, life recognizes clearly them by use of
enzyme stereospecificity. Why life made theexclusive selection of L-type is a great mystery. If
L-system is more stable than D-system on earth, theemergence of L-organism is inevitable consequence.
On the other hand, if both systems have samestability, it is accident. A new law and concept
connecting
monomeric
amino
acid
and
macromolecular polypeptide, will become essential
to answer this question (Fig. 7). Biological molecules
will go through various steps until life are created asa final product. Figure 7 draws up organization levels
for the birth of life from racemic primitive earth
without animate matters with several steps such as
selectivity mechanism, exclusive system, automatism
to higher function and organization, indicating thesignificance of chiral homogeneity to launch theorigin of life. Perhaps the problem on origin ofhomochirality will not be solved until the mechanismof the enzyme stereospecificity are elucidated.
A final goal of spectacular matter’s evolution is
to create living matter, and so the study for origins oflife aims to find a starting line in the magnificent
historical drama that retraces the present life’s path.
However, at the same time, there should be anotherhistorical process preceding biotic evolution. Abiotic
chemical evolution is that process, merely reviewed
as a partial historical scene of matter’s evolution.
Studies of chemical evolution have demonstrated
various biological organic compounds can be
artificially produced through model experiment.
Amino acids can be synthesized with great ease [7].
As a result, no matter how much they are synthesized,
no one can generate life. Abiotic synthesis produces
racemic antipodes in the absence of special catalyst
or chiral reaction field, and thereby any
macromolecule with highly-organized structure
cannot be synthesized. Even assuming arguendo thatenantiometrically-mixed oligopeptide is produced by
accidental synthesis, it will be perfectly impossible to
make the oligopeptide grow into polypeptide withlonger-chain. Life demands strict discrimination evenat lower molecular level as well as higher-order

structure. Whatever be the enantiomeric situation, allbasic biological components such as amino acid andsugar must be completely homochiral to synthesize
life body with ultraprecise stereostructure. For thesynthesis of life, all monomeric molecules should be
supplied kept through one-handed selection
mechanism. Although many bioorganic compounds
as amino acids or sugars are reported by abiotic
synthesis through complicate experiments, it is moredifficult to find how to select, increase and organize
homochiral molecules. When we want to trace aprocess of life’s birth to its origin along a single
street, our first big challenge we cannot get by withavoiding is how chiral homogeneity occurs. We
cannot cut to the knot of it until we open the heavy
gate leading to solve this enigma.
4. How to define life
Unless a life is defined with scientific accuracy,
nobody can determine as a matter of course	  whenlife was born. Although we discuss the origin ofhomochirality without defining life, we should
discuss about it after defining life. Thus we try todefine it again. How was early life born and whatkinds of features did it have? In fact, it is very hard toanswer their questions. For example, think about theidea that DNA is life. If we admit it, a main research
theme of chemical evolution is to study a process ofnatural synthesis of DNA. However, nobody has
succeeded in abiotic experimental synthesis of DNAor creating self-multiplication system without help of
enzyme. How about RNA? Since discovery of
autocatalytic RNA, many researchers have discussed
RNAworld,
but
naturalsynthesisorself-multiplication system of RNA still hasn’t
succeeded in as is the case with DNA. They willprobably conclude DNA or RNA is not life. On theother hand, how about viroid or virus? Perhaps mostof researchers say it is life with the exception of avery tiny minority [9]. Where does this difference
come from? Our view of life agrees to recognize thatlife needs more complex and dynamic substancesystem than DNA and RNA to make itself fulfill its
self-preserving and self-renewal properties. It isestimated that minimal cell size of life require at leasta diameter of 200 nm to regulate their properties [10].
A certain cell size is necessary for inanimate material
to evolve to life. However, element essential for life
is not satisfied only by the size. The difficulties
arising in defining life results from another cause.
There are different cognitive abilities for life todifferent people because they cannot be
non-quantifiable. For example, a feeling ofcomplexity, precision or dynamics are quite different
from person to person. When we observe a computercircuit of CPU or LSI memory, we think it is very
complex and precise. However, no one says E. coli ismore complex. The perfect adjective to describe is
only something called ‘simple’, ‘easy’ or ‘lower’even though it just has more precise and advanced
organized structure than the computer chip! There isanother good example that the cognitive ability forlife depends on people. Japanese people believe thatFig.7	
  To the birth of life from chiral homogeneity44Viva Origino 40 (2012) 40 - 46

spirits dwell in all objects. Fig. 8 is Kaname-isi in
Kashima-jingu Shrine, on which Kashima god sits
neatly as the home. People in old times believed
animate thing dwelt even in a little stone in the way
as well as divine Kaname-isi. How do we today think
about it? Is this an issue which we can afford to laughit off as a joke? Next we think about antemortem andpostmortem change. When a man dies, chemical
analysis of his body will possibly give equivalent
results before and after his death. Nevertheless, we
judge without the slightest hesitation that he is alive
before his death or dead after his death. Why can we
judge so? The reason is that the judgment of life anddeath is independent on the absence or presence ofmaterial. We regard life not as existing materials
itself but as attributes derived from material system.
When the material system cannot depict the attributes,
life becomes inanimate or dead. The material system
must have the capability that can built
highly-organizedstructurefromhomochiralmolecular components. If it lacks the capability, we
cannot accept it as life. It is considered a total of 150
million organism species has been born on this earth
while over 4 billion years have passed since birth oflife. The number of extant species is about 1.75
million, and gene sequence-known species about fifty
thousand. Additionally, organic compounds related tothem is ten million, and enzymes over one hundred
thousand (Known enzymes is no more than about
5000.) [11]. If we sweepingly divide biologicalmetabolic activity into two groups, we can separate
into basic and inherent metabolism. All species sharethe former basic metabolism to maintain vital activity,
while each species has the latter inherent metabolism
to metabolize specific compounds for environmental
adaptation. If both metabolisms are compared to atree, the former is like trunk, and the latter likeperipheral branches and leaves. However, since theinherent metabolism is specific for the organism, it issignificant for the study of environmental adaptationor species diversity to elucidate its metabolic
pathway. Since basic metabolisms are common to allliving organisms, they are primitive. In early life themost primitive metabolism of the basic metabolisms
would be used on early earth. The origin of life isestimated to date back to more than 3.8 billion years
ago on the basis of microfossil data. As today’s life
passes through the stage of amazing adaptive

divergence with various features and functions, weare amazed at their rich diversity at the sight of its
spectacular beauty for a quick moment. However, we
immediately notice that all species and generations
are under common strict principles to keep them alive.
They help enormously in order for a system, which
promotes the production, sustention and developmentof highly-organized structure, to function adequately.
They is shown in the below 1~3.
1.
Preparation of homochiral molecules as
biological components
L-amino acids and D-sugars are basic
components producing highly-organized enzymes or
nucleic acids. It is impossible to make a regularstructure without them.
2.
Continuous exclusion of the opposite
enantiomer
An enantiomer must be always homochiralstatus. However, actual metabolism frequently
produces the opposite enantiomer. Therefore amechanism to exclude it becomes necessary. The best
example is O2-requiring D-amino acid oxidase. Since
the enzyme makes specific degradation to D-aminoacids, it is one of members to constitute the exclusion
system of D-amino acid. The raison d'etre of thisenzyme is to wipe out waste D-amino acid. Hydrogen
peroxide into which D-amino acid is degraded by the
enzyme is subsequently redegraded into O2 and H2O
by catalase. Since the enzyme demands O2, D-aminoacid oxidase will be emerged after the appearance of
atmospheric oxygen, which might revolutionize themetabolic system of early life. D-aspartate is known
to exist in animal baby’s tissue and amnion liquidright after birth [12]. According to Haeckel’s law that
ontogenesis repeats phylogeny, this fact indicates that
D-amino acid is utilized in early metabolism. After
O2 appearance, D-amino acid would become
probably unnecessary life to obtain higher metabolic
efficiency. So D-amino acid oxidase would use
D-amino acid as an oxygen acceptor for biologicaldefense mechanism against O2. It values theannihilation mechanism of superoxide more thanD-aminoacid
degradation.
D-aminoacid
oxidaseperfectly
obliterated
alltracesofenergy-inefficient early life with the assistance of O2.
3.

Continuous restructuring towards a higher level
Life is still evolving without cease to organize
its structure to a higher-level. DNA, whose mutationis largely responsible for biological evolution tocreatehigher-organizedstructure,hasnophysiological activity by itself. In collaboration withother biological molecules, DNA exercises a property
that spontaneously drives life towards higher-level
organization with more advanced functionalization inan efficient way, for example, a sort of hypercycle
mechanism.
This report have discussed about nohomochirality – no life. Life was not born on racemic
early earth until a mechanism of stereoselectivity was

Fig.8 Animate Kaname Stone in Kashima Shrine, thehome of gods and refuge to the spirits.

45

Viva Origino 40 (2012) 40 - 46

incorporated into catalytically active early
polypeptides through spontaneous abiotic process.
Since the mechanism is essential for life, it has been
handed down from generation to generation. It goes
without saying that present enzymes inherit themechanism from their ancestors. Therefore the studyof enzyme stereospecificity will play a key role to a
problem on origin of life and an enigma of life’s birth.
We defined life as a matter system withhighly-organized structure that implements the above
three items. Even though a small stone you pick up in
the side of a road on your way to walking is meager,
you would not find it difficult to feel it is alive if it
has such a high level of organization system. The
time of birth of life is when the enantioselectivity that
ensures the stability of the matter system is first
appeared. The present report has remained mum on
why life makes exclusive selection of L type ofamino acid antipodes. Recent study demonstrates
even if an enzyme has absolute enantioselectivity on
L-amino acid, it becomes active to D-amino acidaccording to solution condition [13]. This indicatesenzyme stereospecificity is indeed flexible. Life
seems to select L type under its control as a matter ofmere expediency because L-exclusive choice issimply too much advantageous to contemporary
environment. The elucidation of its mechanism will
be important to answer the question.
References1.
Miyamoto M., People in a thalidomide disaster − Fromamong serious years, Chikuma Books, Japan (1981).
2.
Ariyoshi Y, K. Yugari, K. Tori, Sweet-tasting substance,
pp.171, in M. Sato Ed.,Gustation and Nutrition, Gustation
Science, Asakura Books, Japan (1981).
3.
Pasteur L., Mémoire sur la fermentation de l’acide tartrique,Comptes Rendus de l’académie des sciences, 46, 615-618(1858).
4.
Cohn E., J. H. Van’t Hoff., Sein Leben und Wirken, Acad.
Verlagsges., Leipzig (1912).
5.
Jakosky B., Unearthing seeps and springs on Mars, The
planetary report, 20, 12-16 (2000).
6.
Bonner W. A., Chirality and life, Origins Life, 25, 175-190(1995).
7.
Harada K., Origin of optical activity and evolution, pp.
145-153, Matter evolution，Chemistry review, 30，Ed.
Chemical Society of Japan (1980).
8.
Green R., Szostak J. W., Selection of a ribozyme thatfunctions as a superior template in a self-copying reaction,
Science, 258, 1910-1915 (1992).
9.
Flores R., A naked plant-specific RNA ten-fold smaller
than the smallest known viral RNA: the viroid, Comptes
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