Exploitation of effective uses of Rubisco as highly functional food resources

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Ribulose bisphosphate carboxylase/oxygenase (Rubisco) which catalizes carbon dioxide fixation in photosynthesis is the most abundant protein on the earth since it occupys 1/3 to 1/2 of leaf proteins. Exceptionally as a plant protein, Rubisco has an ideal amino acid composition from nutritional point of view. We screened for bioactive peptides which might contribute to prevent lifestyle-related diseases in enzymatic digests of Rubisco. Rubiscolin (Tyr Pro-Leu- Asp Leu- Phe), which was isolated as a δ opioid peptide from a pepsin digest of spinach Rubisco, improved learning performance after oral administration at a dose of 100mg/kg in mice. It also exhibited anxiolytic activity. Four inhibitory peptides for angiotensin-converting enzyme, MRWRD, MRW, LRIPVA and IAYKPAG, were isolated from pepsin pancreatin digest of spinach Rubisco. Among them, MRWRD MRW and IAYKPAG showed hypotensive activity after oral administration in spontaneously hypertensive rats (SHR). Crude protein fraction of which Rubisco content was higher than 50% was prepared from spinach and digested with pepsin and pancreatin. ACE-inhibitory activities of the digests from the crude leaf protein were higher than those from purified rubisco. Especially, pepsin digest of the crude leaf protein exhibited potent antihypertensive activity suggesting that ingestion of leaf protein is effective in preventing hypertension. Essentially the same bioactive peptides could be released from Rubisco of other plant species. Rubisco is expected as an ideal protein resouce which could be produced under small environmental load.Rubisco is an important enzyme protein in lowering atmospheric carbon dioxide. This means that Rubisco is a very important proteins not only as a food resources but also in improving environment.