Mycosporine-like amino acids (MAAs) are the ultraviolet (UV)-absorbable compounds, which are naturally produced by cyanobacteria and algae. Not only these algae but also marine organisms utilize MAAs to protect their DNA from UV-induced damage. On the other hand, the content of MAAs in algae was changed by the environmental condition and season. In addition to the UV-protected function, the antioxidant capacity of MAAs can apply to the cosmetic sunscreen materials and anti-cancer for human health. In this study, we developed the efficient extraction method of MAAs from red alga dulse in Usujiri (Hokkaido, Japan) and investigated the monthly variation. We also evaluated the antioxidant capacity. We employed the successive extraction method of water and then methanol extraction. Spectrophotometric and HPLC analyses revealed that the yield of MAAs by 6 h water extraction was the highest among the tested conditions, and the content of MAAs in the sample of February was the most (6.930 µmol g⁻¹ dry weight) among the sample from January to May in 2019. Antioxidant capacity of MAAs such as crude MAAs, the purified palythine and porphyra-334 were determined by 2,2’-azinobis(3-ethylbenzothiazoline 6-sulfonic acid) (ABTS) radical scavenging and ferrous reducing power assays in various pH conditions, showing that the highest scavenging activity and reducing power were found at alkaline condition (pH 8.0).

In this study, we characterized the bioactive properties of three important brown seaweed species, Sargassum thunbergii, Undaria pinnatifida, and Saccharina japonica, by subcritical water extraction (SWE), as these species are well known for their beneficial health effects. Their physiochemical properties, including potential antioxidant, antihypertensive, and α-glucosidase inhibitory activity, and the antibacterial activity of the hydroysates were also analyzed. The highest total phlorotannin, total sugar content, and reducing sugar content in the S. thunbergii hydrolysates were 38.82 ± 0.17 mg PGE/g, 116.66 ± 0.19 mg glucose/g dry sample, and 53.27 ± 1.57 mg glucose/g dry sample, respectively. The highest ABTS⁺ and DPPH antioxidant activities were obtained in the S. japonica hydrolysates (124.77 ± 2.47 and 46.35 ± 0.01 mg Trolox equivalent/g, respectively) and the highest FRAP activity was obtained in the S. thunbergii hydrolysates (34.47 ± 0.49 mg Trolox equivalent/g seaweed). In addition, the seaweed extracts showed antihypertensive (≤59.77 ± 0.14%) and α-glucosidase inhibitory activity (≤68.05 ± 1.15%), as well as activity against foodborne pathogens. The present findings provide evidence of the biological activity of brown seaweed extracts for potential application in the food, pharmaceutical, and cosmetic sectors.

More than 7000 red algae species have been classified. Although most of them are underused, they are a protein-rich marine resource. The hydrolysates of red algal proteins are good candidates for the inhibition of the angiotensin-I-converting enzyme (ACE). The ACE is one of the key factors for cardiovascular disease, and the inhibition of ACE activity is related to the prevention of high blood pressure. To better understand the relationship between the hydrolysates of red algal proteins and the inhibition of ACE activity, we attempted to identify novel ACE inhibitory peptides from Pyropia pseudolinearis. We prepared water soluble proteins (WSP) containing phycoerythrin, phycocyanin, allophycocyanin, and ribulose 1,5-bisphosphate carboxylase/oxygenase. In vitro analysis showed that the thermolysin hydrolysate of the WSP had high ACE inhibitory activity compared to that of WSP. We then identified 42 peptides in the hydrolysate by high-performance liquid chromatography and mass spectrometry. Among 42 peptides, 23 peptides were found in chloroplast proteins. We then synthesized the uncharacterized peptides ARY, YLR, and LRM and measured the ACE inhibitory activity. LRM showed a low IC₅₀ value (0.15 μmol) compared to ARY and YLR (1.3 and 5.8 μmol). In silico analysis revealed that the LRM sequence was conserved in cpcA from Bangiales and Florideophyceae, indicating that the novel ACE inhibitory peptide LRM was highly conserved in red algae.

In this study, we studied the bioactive peptides produced by thermolysin hydrolysis of a water-soluble protein (WSP) from the red alga Gracilariopsis chorda, whose major components are phycobiliproteins and Ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCo). The results showed that WSP hydrolysate exhibited significantly higher ACE inhibitory activity (92% inhibition) compared to DPP-IV inhibitory activity and DPPH scavenging activity. The phycobiliproteins and RuBisCo of G. chorda contain a high proportion of hydrophobic (31.0–46.5%) and aromatic (5.1–46.5%) amino acid residues, which was considered suitable for the formation of peptides with strong ACE inhibitory activity. Therefore, we searched for peptides with strong ACE inhibitory activity and identified two novel peptides (IDHY and LVVER). Then, their interaction with human ACE was evaluated by molecular docking, and IDHY was found to be a promising inhibitor. In silico analysis was then performed on the structural factors affecting ACE inhibitory peptide release, using the predicted 3D structures of phycobiliproteins and RuBisCo. The results showed that most of the ACE inhibitory peptides are located in the highly solvent accessible α-helix. Therefore, it was suggested that G. chorda is a good source of bioactive peptides, especially ACE-inhibitory peptides.

Plastid proteins are one of the main components in red algae. In order to clarify the angiotensin I converting enzyme (ACE) inhibitory peptides from red alga Palmaria sp. (Japan), we determined the plastid genome sequence. The genome possesses 205 protein coding genes, which were classified as genetic systems, ribosomal proteins, photosystems, adenosine triphosphate (ATP) synthesis, metabolism, transport, or unknown. After comparing ACE inhibitory peptides between protein sequences and a database, photosystems (177 ACE inhibitory peptides) were found to be the major source of ACE inhibitory peptides (total of 751). Photosystems consist of phycobilisomes, photosystem I, photosystem II, cytochrome complex, and a redox system. Among them, photosystem I (53) and II (51) were the major source of ACE inhibitory peptides. We found that the amino acid sequence of apcE (14) in phycobilisomes, psaA (18) and psaB (13) in photosystem I, and psbB (11) and psbC (10) in photosystem II covered a majority of bioactive peptide sequences. These results are useful for evaluating the bioactive peptides from red algae.

Red alga dulse possesses a unique xylan, which is composed of a linear β-(1→3)/β-(1→4)-xylosyl linkage. We previously prepared characteristic xylooligosaccharide (DX3, (β-(1→3)-xylosyl-xylobiose)) from dulse. In this study, we evaluated the prebiotic effect of DX3 on enteric bacterium. Although DX3 was utilized by Bacteroides sp. and Bifidobacterium adolescentis, Bacteroides Ksp. grew slowly as compared with β-(1→4)-xylotriose (X3) but B. adolescentis grew similar to X3. Therefore, we aimed to find the key DX3 hydrolysis enzymes in B. adolescentis. From bioinformatics analysis, two enzymes from the glycoside hydrolase family 43 (BAD0423: subfamily 12 and BAD0428: subfamily 11) were selected and expressed in Escherichia coli. BAD0423 hydrolyzed β-(1→3)-xylosyl linkage in DX3 with the specific activity of 2988 mU/mg producing xylose (X1) and xylobiose (X2), and showed low activity on X2 and X3. BAD0428 showed high activity on X2 and X3 producing X1, and the activity of BAD0428 on DX3 was 1298 mU/mg producing X1. Cooperative hydrolysis of DX3 was found in the combination of BAD0423 and BAD0428 producing X1 as the main product. From enzymatic character, hydrolysis of X3 was completed by one enzyme BAD0428, whereas hydrolysis of DX3 needed more than two enzymes.