Cationic Ascorbate Peroxidase Isoenzyme II from Tea: Structural Insights into the Heme Pocket of a Unique Hybrid Peroxidase

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• 作者：Hendrik A. Heering ; Marcel A. K. Jansen ; Roger N. F. Thorneley ; and Giulietta Smulevich
• 刊名：Biochemistry
• 出版年：2001
• 出版时间：August 28, 2001
• 年：2001
• 卷：40
• 期：34
• 页码：10360 - 10370
• 全文大小：142K
• 年卷期：v.40,no.34(August 28, 2001)
• ISSN：1520-4995

文摘

The novel class III ascorbate peroxidase isoenzyme II from tea leaves (TcAPXII), with anunusually high specific ascorbate peroxidase activity associated with stress response, has been characterizedby resonance Raman (RR), electronic absorption, and Fourier transform infrared (FT-IR) spectroscopies.Ferric and ferrous forms and the complexes with fluoride, cyanide, and CO have been studied at variouspH values. The overall blue shift of the electronic absorption spectrum, the high RR frequencies of thecore size marker bands, similar to those of 6-coordinate low-spin heme, and the complex RR spectrum inthe low-frequency region of ferric TcAPXII indicate that this protein contains an unusual 5-coordinatequantum mechanically mixed-spin heme. The spectra of both the fluoride and the CO adducts suggestthat these exogenous ligands are strongly hydrogen-bonded with a residue that appears to be unique tothis peroxidase. Electronic absorption spectra also emphasize structural differences between thebenzhydroxamic acid binding sites of TcAPXII and horseradish peroxidases (HRPC). It is concluded thatTcAPXII is a paradigm peroxidase since it is the first example of a hybrid enzyme that combinesspectroscopic signatures, structural elements, and substrate specificities previously reported only for distinctclass I and class III peroxidases.