Iodine identification in major edible seaweed Kappaphycus alvarezii and establishment of an iodine reduction method for its protein extract for utilization as a protein source.

Kappaphycus alvarezii is the most widely cultivated seaweed globally. The use of the protein contained in K. alvarezii as an alternative protein source seems to be an effective countermeasure against the protein crisis. Here, we identified the iodine chemical species in K. alvarezii and developed an iodine reduction method. We used various fractionation methods and showed that almost all the iodine in the K. alvarezii alkali extract is present as an iodinated protein, and reducing the amount of iodine per protein was difficult. Subsequently, an iodine reduction method was established to cleave the covalent bonds between the protein and iodine, and we could successfully reduce the amount of iodine per protein by approximately half.

The degradation of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase into the 44-kDa fragment in the lysates of chloroplasts incubated in darkness.

Lysates of chloroplasts isolated from naturally senescing wheat leaves were incubated in darkness. The 44-kDa fragment, lacking the N-terminal-side portion of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (LSU), was found by immunoblotting with the LSU site-specific antibodies. Analysis of its N-terminal amino acid sequence indicated that the LSU was specifically cleaved at the peptide bond between Phe-40 and Arg-41. The site was located on the surface of the molecule and faced outward. Such cleavage of the LSU has not been previously reported. It is indicated that the cleavage was triggered by an unknown protease existing in chloroplasts.