Divergent biochemical and enzymatic properties of oxalate oxidase isoforms encoded by four similar genes in rice.
The biochemical and enzymatic properties of four highly similar rice oxalate oxidase proteins (OsOxO1-4) were compared after their purification from the leaves of transgenic plants each overexpressing the respective OsOxO1-4 genes. Although alignment of their amino acid sequences has revealed divergence mainly in the signal peptides and they catalyze the same enzymic (oxalate oxidase) reaction, divergence in apparent molecular mass, Km, optimum pH, stability and responses to inhibitors and activators was uncovered by biochemical characterization of the purified OsOxO1-4 proteins. The apparent molecular mass of oligomer OsOxO1 was found to be similar to that of OsOxO3 but lower than the other two. The molecular mass of the subunit of OsOxO1 was lower than that of OsOxO3. The Km value of OsOxO3 was higher than the other three which had similar Km. OsOxO1 and OsOxO4 possessed peak activity at pH 8.5 which was close to that at the optimum pH 4.0. The activity of OsOxO2 at pH 8.5 was only 65% of that at its optimum pH 3.5, while the activity of OsOxO3 did not vary much at pH 6-9 and was also much lower than that at its optimum pH 3. OsOxO2 and OsOxO3 still maintained all their activities after being heated at 70°C for 1h while OsOxO1 and OsOxO4 lost about 30% of their activities. Pyruvate and oxaloacetic acid inhibited the activity of OsOxO3 more strongly than the other three. Interestingly, glucose 6-phosphate, fructose 6-phosphate and fructose 1,6-biphosphate related to photosynthetic assimilation of triose phosphate greatly increased the activities of OsOxO3 and OsOxO4. In addition to the differences in the biochemical properties of the four OsOxO proteins, an intriguing finding is that the purified OsOxO1-4 exhibited substrate inhibition, which is a typical of the classical Michaelis-Menten enzyme kinetics exhibited by a majority of other enzymes.
College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
Xiao Chun
XC
Li
College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
Yuan Yang
YY
Liao
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand.
David W M
DW
Leung
College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
Hai Yan
HY
Wang
College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
Bai Ling
BL
Chen
College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
Xin Xiang
XX
Peng
College of Life Sciences, South China Agricultural University, Guangzhou 510642, China. Electronic address: eeliu70@163.com.
E E
EE
Liu
D000595:Amino Acid Sequence; D007527:Isoenzymes; D008970:Molecular Weight; D012275:Oryza / Q000201:enzymology* / Q000235:genetics*; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry; D030821:Plants, Genetically Modified / Q000378:metabolism
D007527:Isoenzymes; D010088:Oxidoreductases; C020598:oxalate oxidase
Allosteric regulation; Enzyme activation; Fructose-1,6-biphosphate; Glucose-6-phosphate; Gramineae; Oryza sativa; Oxalate oxidase; Substrate inhibition (of enzymes)