Abstract: Essentially pure curculin B is disclosed. A process for producing curculin B, includes the steps of: culturing a transformed cell or microorganism containing a recombinant DNA containing a base sequence encoding curculin B, whereby curculin B is produced by the transformed cell or microorganism, and isolating curculin B from the transformed cell or microorganism. A DNA encoding mature or premature curculin B is also disclosed.

Abstract: An antifreezing agent used in an aqueous medium system comprising a protein which is enzymatically modified with covalent incorporation of an amino acid ester. The antifreezing agent can keep an unfrozen state of the system down to -10.degree. C., and does not exert any harmful effect to biological bodies.

Abstract: A modified protein composition which is produced by contacting a water-soluble protein, such as plant seed proteins, cow milk protein, animal meat proteins, fish meat proteins, egg proteins and microorganisms proteins, with a cysteine-enriched plastein in an amount of at least 1% by weight on the basis of the water-soluble protein in an aqueous medium, and if desired, heating the resultant under a mild condition (e.g. at a temperature of 40.degree. to 90.degree. C.), said cysteine-enriched plastein being produced by hydrolyzing a protein with an enzyme having an endopeptidase activity and subjecting the hydrolyzate to dehydration-condensation with a protease having an esterase activity in the presence of an activated cysteine (e.g. lower alkyl cysteinate, N-acetyl-L-cysteine or L-cysteinyl-L-cysteine).

Abstract: Method for the preparation of a low-phenylalanine plastein comprising hydrolyzing stepwise a certain albumin or globulin protein with an endopeptidase having an affinity for the aromatic acid components, and an exopeptidase, subjecting the hydrolyzate thus-obtained to gel-filtration to divide it into two fractions, one being constituted with aromatic amino acids and the other being constituted with oligopeptides almost free from the aromatic amino acids, and then subjecting the latter fraction to usual plastein synthesis. Tyrosine and/or tryptophan may be added to the substrate at the plastein synthesis in order to incorporate them into the plastein molecules. The resultant plasteins may be purified through ultra-filtration in order to remove the remaining free amino acids and low-molecular peptides.