Bot. Bull. Acad. Sin. (1995) 36: 81-87

Lin and Yao Onion protease activities

Onion (Allium cepa L.) contains some high proteolytic activities already before germination

Yaw-Huei Lin1 and Wen-Hsiang Yao

Institute of Botany, Academia Sinica, Taipei, Taiwan 115, Republic of China

(Received December 7. 1994; Accepted March 8. 1995)

Abstract. Onion bulbs had higher proteinase and carboxypeptidase activity levels before germination than after, when casein or hemoglobin was used as a substrate. The substrates that were hydrolyzed most rapidly before germination, Hip-Gly Gly and Hip-Lys, were different from those which were hydrolyzed most rapidly after germination, Hip-Gly-Lys and Hip-His-Leu. Amino peptidase and some endopeptidase activities were determined before and after germination using 4-nitroaniline or b-naphthylamine derivatives of amino acids or peptides as substrates at pH 3.4, 7.0, or 8.9. Before germination, Gly-Na and Phe-Na were hydrolyzed most rapidly at all three pHs: and Gly-Na, Phe-Na, and Ala-Na were hydrolyzed most rapidly at both pH 7.0 and 8.9. 4-nitroaniline derivatives of peptides were hydrolyzed substantially, although not most rapidly, at all pHs. Phe-Nap was hydrolyzed most rapidly at pH 3.4 and 7.0 while Ala-Nap was hydrolyzed most rapidly at pH 8.9. Phe-Nap, Lys-Nap, Ala-Nap, and Arg-Nap were among the 5 leading substrates at all pHs. After germination, Gly-Na and Phe-Na were hydrolyzed most rapidly at pH 3.4 and 7.0 (the same as before germination), and Phe-Na, Ala-Ala-Phe-Na and Gly-Na were hydrolyzed most rapidly at pH 8.9. Ala-Ala-Ala-Na and Ala-Ala-Phe-Na were hydrolyzed rather rapidly at pH 3.4 and 8.9, respectively, which was not observed before germination. Cbz-Phe-Nap, Phe-Nap, and Trp-Nap were hydrolyzed most rapidly at pH 3.4, 7.0, and 8.9, respectively. Cbz-Phe-Nap and Ben-Phe-Nap were hydrolyzed most rapidly at pH 3.4 (characteristic of germinating onion bulbs). Variance analysis (using Gly-Na as substrate) shows that pH (P) and days after imbibition (D) were significant sources of variance. There was also interaction between P and D. Details of interaction between P and D with various substrates were analyzed by Scheffe's difference comparison.

Keywords: Germination: Onion; Protease activities: Synthetic substrates.

Abbreviations: Ace, acetyl; Ben, benzoyl; Cbz, benzylcarbonyl: methoxy: Na, nitroanilide: Nap, naphthylamide.

1Corresponding authors.