About the protein component of dulse

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• General

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• Background
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    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)
    
    ダルス：dulse
    
    

• Structural characteristics of phycobiliproteins from dulse
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    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 chlorophyll cannot.

    
    

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    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.

    
    

     

    
    

    
    

    フィコビリタンパク質：phycobiliproteins
    葉緑体：chloroplast
    フィコシアニン：phycocyanin
    アロフィコシアニン：allophycocyanin
    フィコエリスリン：phycoerythrin
    フィコビリソーム：phycobilisome
    
    
    

• 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 intestine.

    
    

    2) Angiotensin I-converting enzyme (ACE) inhibition

    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 inhibitory peptide.

    
    

    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.

    
    

• Source
  • Oyashio (Hokusui alumni magazine) No. 305 (2015)

    KISHIMURA Hideki (Sho 60 Ka)

    
    

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