Environmental
biochemistry
A
Novel Antioxidant Derived from
Seaweed
WC Dunlap1,
K Masaki2,
Y Yamamoto3,
RM Larsen4
and I Karube3
1Australian Institute
of Marine Science,
2Toyo
Suisan Kaisha Ltd,
3Research
Center for Science and Technology,
University of Tokyo,
4Sir
George Fisher Centre, James Cook
University
Presentation
to the 4th International Marine
Biotechnology Conference, Sorrento,
September 23, 1997 [1].
Many organisms inhabiting
shallow-water or inter-tidal marine
environments are protected from long-term
solar damage by producing natural,
UV-absorbing sunscreens of the generic
class known as mycosporine amino acids (MAAs) [2]. These
compounds are derived from the shikimic
acid pathway [3] via
3-dehydroquinic acid and 4-deoxygadusol
(4-DG). Mycopsorines were first
discovered in terrestrial fungi [4]
and these metabolites are believed to
provide UV protection to fungal spores
while exposed to solar radiation during
atmospheric dispersal [5].
The UV-B
region overlaps with the long-wavelength
absorptions of DNA and is largely
responsible for the chronic damage caused
by sunlight. However, many other cellular
components (biomolecules) can also absorb
UV-A and UV-B radiation leading to
photodynamically generated, reactive
oxygen intermediates, such as singlet
oxygen, superoxide anion, and peroxyl and
hydroxyl radicals (Fig. 1.), having the
potential to cause acute oxidative damage
[6]. Aerobic organisms
have evolved a variety of defenses
against oxidative damage. Essentially,
these antioxidative defences are of three
general classes which include
water-soluble reductants (antioxidants)
in the cytosol, fat-soluble reductants
residing in cellular membranes, and
antioxygenic defence enzymes which
deactivate the reactive oxygen
by-products formed in the
reduction-oxidation (redox) cycling of
cellular metabolism, principally in the
mitochondria. Antioxygenic enzymes are a
common evolutionary feature of all living
organisms and their function in marine
organisms are well established [7].
In contrast, the biofunction of
small-molecule antioxidants (reductants)
in the photophysiology of marine
organisms is yet poorly understood.
Fig. 1.
Simplified
diagram for the photodynamic generation
of reactive oxygen species (ROS)
in
marine organisms.
A
collaborative study was initiated to
investigate the possible relationship
between UV-absorbing and antioxidant
functions of MAAs. We found that
imino-mycosporines are oxidatively inert
while oxo-carbonyl mycosporines
(mycosporine-glycine and
mycosporine-taurine) are moderately
active [8]. The MAA
precursor 4-deoxygadusol, however, was
found to be a strong antioxidant with
activity comparable to that of ascorbate [9].
Many species of marine algae are rich in imino-MAAs. In a prior study [10]
we found that the marine bacterium Vibrio
harveyi efficiently converts algal MAAs, shinorine and porphyra-334, to
mycosporine-glycine in the enteric
process of MAA absorption in
deposit-feeding holothurians leading to
the trophic accumulation of asterina-330
(Fig. 2) [11]. Further investigation
revealed that algal MAAs could be
converted in moderate yield to the active
4-DG antioxidant (a metabolite found in
the eggs of fish [12, 13]
and sea urchins [14]) on
fermentation with either an unidentified Vibrio
sp. (RML017) or with several species from
the genus Pseudoalteromonas.
Toyo Suisan is investigating the
commercial production of 4-DG using this
"retro-biosynthetic" pathway
for intended use as a natural antioxidant
in food-processing and cosmetic
applications [9].
Fig. 2.
Proposed scheme for the bioconversion of
algal MAAs (shinorine and porphyra-334)
to asterina-330 in tropical holothuroids,
and biosynthetic conversion to the strong
antioxidant, 4-deoxygadusol.
Mycosporine-glycine
is a predominant MAA component in coral
symbiosis [15]. As well
as functioning as a natural sunscreen (lmax= 310 nm), this MAA also has
moderate antioxidant activity and may
provide some relief against
photooxidative stress in the hyperoxic
tissues of algal-invertebrate symbiosis [16].
The presumed biochemical precursor of MAAs, 4-deoxygadusol (4-DG), is often
observed in marine autotrophs and in
autotrophic symbiosis together with MAAs
(Dunlap, pers. observation), and has
strong antioxidant properties. The
antioxidant activities of
mycosporine-glycine and 4-deoxygadusol
are demonstrated by the
phosphatidylcholine (PC) peroxidation
inhibition assay [17] by
which these antioxidant compounds retard
the rate of chemically-initiated,
free-radical hydroperoxidation of PC in
vitro (Fig. 3). While the functional
abilities, metabolic fate and possible
cycling of these antioxidants in
algal-invertebrate symbioses are yet
unknown, the oxidative robustness of
imino-mycopsorines is in keeping with
their primary role as stable biological
sunscreens in coral reef organisms [8].
Fig. 3.
Phosphatidylcholine
(PC) peroxidation inhibition assay for
purified shinorine, mycosporine-glycine (Myc-Gly) and 4-deoxygadusol (4-DG).
PC-OOH is the phosphatidylcholine
hydroperoxide product of PC oxidation;
antioxidant activity is determined by the
inhibition of the control rate of
oxidation.
References:
[1]
Dunlap WC, Masaki K, Yamamoto Y, Larsen
RM and Karube I (in press). A novel
antioxidant derived from seaweed. In: Recent
Developments in Marine Biotechnology
(eds. Le Gal Y and Halvorson H), Plenum
Press.
[2]
Dunlap WC, Chalker BE and Oliver JK
(1986). Photoadaptation by reef-building
corals from Davies Reef, Great Barrier
Reef, Australia. III. UV-B absorbing
pigments. J. Exp. Mar. Biol. Ecol. 104:
239-248.
[3]
Bently R (1990). The shikimate pathway -
a metabolic tree with many branches. Crit.
Rev. Biochem. 25:307-384.
[4]
Favre-Bonvin J, Arpin N and Brevard C
(1976). Structure de la mycosporine
(P310). Can J. Chem. 54:1105-1113.
[5]
Young H and Patterson VJ (1982). A UV
protective compound from Glomerella cingulata
- a mycosporine. Phytochem.
21:1075-1077.
[6]
Tyrell, R.M. UV-A (320-380 nm) radiation
as an oxidative stress. Oxidative
stress: oxidants and antioxidants
(H. Sies, ed.), pp 57-83, Academic Press,
San Diego (1991).
[7]
Di Giulio, R.T., Washburn, P.C., Wenning,
R.J., Winston, G.W. and Jewell, C.S.
Biochemical responses in aquatic animals:
A review of determinants of oxidative stress.
Environ. Toxicol. Chem. 8, 1103-1123
(1981).
[8]
Dunlap WC and Yamamoto Y (1995).
Small-molecule antioxidants in marine
organisms: antioxidant activity of
mycosporine-glycine. Comp. Biochem.
Physiol. 112B:105-114.
[9]
Masaki K, Dunlap WC, Yamamoto Y, Karube
I, Larsen RM and Matsukawa R (1996). A
natural antioxidant and its production
process. Toyo Suisan Kaisha Pty. Ltd.
Japanese Patent Application No. 9604230,
23 September, 1996.
[10]
Masaki K, Masuchi Y, Akagawa-Matsushita
M, Dunlap WC and Karube I (submitted).
Novel marine bacteria producing the
antioxidant 4-deoxygadusol from algal
mycosporine-like amino acids. J. Ind. Microbiol.
Biotechn.
[11]
Shick JM, Dunlap WC, Chalker BE, Banaszak
AT, Rosenzweig TK (1992). Survey of
ultraviolet radiation absorbing
mycosporine-like amino acids in organs of
coral reef holothuroids. Mar. Ecol.
Prog. Ser. 90: 139-148.
[12]
Chioccara F, Della Gala A and De Rosa M
(1980). Mycosporine amino acids and
related compounds from the eggs of
fishes. Bull. Soc. Chim. Belg.
89:1101-1106.
[13]
Plank PA, Fraser NW, Grant PT, Middleton
C, Michell AI and Thompson RH (1981). Gadusol, an enolic derivative of
cyclohexane-1,3-dione present in the roes
of cod and other marine fish. Biochem.
J. 199:741-742.
[14]
Chioccara F, Zeuli L and Novellino E
(1986). Occurrence of mycosporine related
compounds in sea urchin eggs. Comp.
Biochem. Physiol. 80B: 459-461.
[15]
Dunlap WC and Shick JM (in press).
Ultraviolet radiation-absorbing
mycosporine-like amino acids in coral
reef organisms: a biochemical and
environmental perspective. J. Phycol.
[invited review].
[16]
Kuhl M, Cohen Y, Dalsgaard T,
Jorgensen BB and Revsbech NP (1995).
Microenvironment and photosynthesis of
zooxanthellae in scleractinian corals
studied with microsensors for O2, pH and
light. Mar. Ecol. Progr. Ser.
117:159-172.
[17]
Niki E (1990). Free radical initiators as
source of water- or lipid-soluble peroxyl
radicals. In: Packer, L. and
Glazer, A.N. [eds.] Oxygen radical in
biological systems. Part B. Oxygen
radicals and antioxidants. Methods in
Enzymology 186:100-108, Academic
Press, New York.
For
further information contact
Email: Dr Walter C Dunlap - AIMS
Townsville
Telephone: +61 (07) 47534365
 AIMS home page
web@aims.gov.au
Last updated -
December 18, 2008
Copyright ©1996-2002 Australian Institute of Marine Science
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