tailieunhanh - Báo cáo khoa học: "Excretion of laccase by sycamore (Acer pseudoplatanus cambial cells: effect of copper deficiency, reversible removal of type 2 Cu 2+ "

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài:"Excretion of laccase by sycamore (Acer pseudoplatanus cambial cells: effect of copper deficiency, reversible removal of type 2 Cu 2+. | 860s Ann. Sci. For. 1989 46 suppl. 860S-863S Forest Tree Physiology E. Dreyer etal. eds. Elsevier INRA Excretion of laccase by sycamore Acer pseudoplatanus L. cambial cells effect of copper deficiency reversible removal of type 2 Cu2 J. Quinton-Tulloch1 J. Gaillard2 J. Jordanov2 R. Bligny1 and R. Douce1 CEN-G et Université Joseph-Fourier DRF PCVi and DRF SCPM2 85X F-38041 Grenoble Cedex France Introduction Cambial cells of sycamore excrete a laccase-type polyphenol oxidase EC Bligny and Douce 1983 . This type of enzyme which utilizes molecular oxygen to oxidize phenolic substrates is probably involved in lignin degradation processes Mayer and Harel 1979 . This polyphenol oxidase is excreted by many mycorrhizal fungi for a review see Mayer 1987 and is present in some higher plant cells including the genus Rhus Rhus ver-nicifera see Reinhammar 1970 Aescu-lus Wosilait et al. 1954 and Prunus Lehman et al. 1974 . The enzyme was purified from the nutrient medium into which it was excreted by suspension-cultured sycamore cells using classical purification techniques including a concanava-lin A-Sepharose affinity column. The sycamore cell laccase is a monomeric blue copper protein containing 45 carbohydrate and 4 copper atoms one type 1 and 2 Cu2 and two type 3 Cu2 per molecule. The molecular mass Mr 97 000 was calculated from the sedimentation coefficient s20 w the diffusion coefficient P20w and the partial specific volume v . The specific activity of the purified enzyme measured at pH optimum pH and in the presence of 20 mM 4-methylcatechol optimum substrate conditions corresponds to an oxygen uptake of at least 32 pmol of consumed o2 min mg of protein. The structure of the protein is stabilized by asparagine-linked oligosaccharides which are a series of recurrent xylose-containing biantennary complexes that share at the core a common structural unit . Xylj3 1 - 2 Mana 1- 6 Man 3 1 - 4GlcNAc 3 1 - 4 Fuca 1 3 GlcNAc Takahashi ef al. 1986 . .