In vitro activation of pro-phenol-oxidase by two kinds of pro-phenol- oxidase-activating factors isolated from hemolymph of coleopteran, Holotrichia diomphalia larvae

So Young Lee, Tae Hyuk Kwon, Ji Hoon Hyun, Jae Sue Choi, Shun-Ichiro Kawabata, Sadaaki Iwanaga, Bok Luel Lee

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Previously, we purified and characterized a pro-phenol-oxidase (pro-PO) of 79 kDa from coleopteran insect, Holotrichia diomphalia larvae [Kwon et al. (1997) Mol. Cells 7, 90-97]. Here, we describe the identification of two pro- PO-activating factors (PPAF), named PPAF-I and PPAF-II, directly involved in the activation of the isolated pro-PO. When pro-PO was incubated with either PPAF-I or PPAF-II, no phenol oxidase activity was observed. However, incubation of pro-PO with both PPAF-I and PPAF-II specifically exhibited phenol oxidase activity. The purified PPAF-I with a molecular mass of 33 kDa on SDS/PAGE had characteristics of a serine protease. It exhibited amidase activity against fluorogenic peptide substrates, tert-butoxycarbonyl- phenylalanyl-seryl-arginyl-4-methylcoumaryl-7-amide being the best among the substrates examined. The activity was completely inhibited by 0.02 mM p- nitrophenylp'-guanidinobenzoate HCl and diisopropylflurophosphate. The NH2- terminal sequence of PPAF-I had significant sequence similarity to those of serine proteases. On the other hand, the purified PPAF-II had a molecular mass of 40 kDa on SDS/PAGE and 400 kDa determined by gel filtration, indicating an oligomeric protein. The NH2-terminal sequence of PPAF-II showed no similarity to known proteins. PPAF-II exhibited no amidase activity against the fluorogenic substrates. Reconstitution experiments and immunoblotting analysis using affinity-purified antibody against pro-PO demonstrated that PPAF-I first cleaves the intact pro-PO to an intermediate of 76 kDa with no phenol oxidase activity, and then, PPAFI converts the intermediate to the active phenol oxidase of 60 kDa in the presence of PPAF- II. These results indicate that the activation of pro-PO system in hemolymph of H. diomphalia larvae is accomplished by at least two activating factors, a serine protease and a protein cofactor.

Original languageEnglish
Pages (from-to)50-57
Number of pages8
JournalEuropean Journal of Biochemistry
Issue number1
Publication statusPublished - May 15 1998


All Science Journal Classification (ASJC) codes

  • Biochemistry

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