In the Minami-Kayabe area of southern
Hokkaido, red algae of the genus Palmaria (hereafter referred to as “dulse”)
naturally thrive on kelp culture ropes during the winter. The dulse is regarded
by growers as a nuisance because it hinders the growth of cultivated kelp by
preventing it from being exposed to sunlight. However, recent component
analysis has revealed that dulse is rich in nutrients such as protein, dietary
fiber, potassium, and B vitamins.
Against this background, we have been
conducting research on structural characterization of pigment proteins
abundantly contained in dulse and their health functionality with the aim of
effectively utilizing this underutilized resource. In this page, we briefly
introduce the results obtained to date.
■Photo by Dr. YASUI Hajime (Sho 55 Zo)
Structural characteristics of phycobiliproteins from dulse
When water is added to a dried dulse
sample, the red component is easily extracted. The color of the extract is
bright red in sunlight and fluoresces strongly when illuminated by green light.
These characteristics are attributed to “phycobiliprotein”, the major protein
in the dulse phloem. In red algae, phycobiliprotein acts as an auxiliary
pigment for photosynthesis, efficiently absorbing light at wavelengths that
ダルスタンパク質：dulse protein 水性赤インク： aqueous red ink 太陽光：sunlight グリーンライト： green light
In general, phycobiliproteins of red algae
are mainly composed of two types of subunits, α- and β-chains, which form
circular doughnut-like assemblies consisting of three each of them. These
doughnut-like structures are then further assembled to form a large aggregate
called a phycobilisome. Phycobilisomes are arranged in large numbers on the
surface of the chloroplast thylakoid membrane. The major phycobiliproteins of
red algae are phycoerythrin (red), phycocyanin (blue), and allophycocyanin
(purple). Their coloration is determined by the type of the pigment (phycoerythrobilin,
phycocyanobilin, or phycourobilin) that bound apoprotein of α- and β-chains and number.
Protein extracts prepared from dulse were
subjected to spectral analysis, which revealed that the main component of
phycobiliproteins from dulse is red phycoerythrin, followed by phycocyanin and
allophycocyanin. Therefore, dulse phycoerythrin was purified and crystals were
prepared, and its three-dimensional structure was determined by X-ray
crystallography. As a result, dulse phycoerythrin had the same
three-dimensional structural characteristics as those of other red algae. In
addition, to elucidate the genetic structure of phycobiliproteins from dulse,
chloroplast DNA encoding the genes of phycobiliproteins was analyzed by a
next-generation sequencer. As a result, the gene structures and primary
structures of three phycobiliproteins (phycoerythrin, phycocyanin, and
allophycocyanin) were clarified.
Health functionality of phycobiliproteins from dulse
1) Inhibition of blood glucose level rise
In recent years, the number of diabetics in
Japan has tended to increase year by year due to changes in diet and lifestyle.
Therefore, we conducted an animal study to investigate the effect of a protein
prepared from dulse (dulse protein) on the suppression of elevated blood
glucose levels. The results showed that dulse protein significantly suppressed
the increase in blood glucose levels after glucose loading. We now speculate
that dulse protein may inhibit the absorption of glucose in the small
Treatment and prevention of hypertension is
an important issue because if left untreated, it causes arteriosclerosis, which
in turn leads to various vascular diseases such as heart disease and stroke.
Therefore, the ACE inhibitory effect of dulse protein was investigated. As a
result, a peptide (dulse peptide) hydrolyzed by protease from dulse protein was
found to have a strong ACE inhibitory effect. Next, the dulse peptides were
fractionated and the amino acid sequences of the active peptides were
determined, and we found that many of these sequences were present in the
primary structure of dulse-derived phycoerythrin. Based on these results, we
speculate that phycoerythrin is the primary protein that derived the dulse ACE
3) Antioxidant action
It has been revealed that oxidative damage
to living organisms caused by reactive oxygen species is a cause of aging and
various diseases, and foods rich in antioxidants are attracting attention. Therefore,
we investigated the antioxidant effects of dulse protein using radical
scavenging activity as an indicator. As a result, antioxidant activity was
observed in dulse protein. On the other hand, the pigmentless dulse
phycoerythrin expressed in coli bacteria showed almost no antioxidant activity.
This indirectly suggested that the major site of antioxidant activity of dulse
protein is the pigmented part, not the apoprotein part.