To investigate the enzyme properties of the black sesame polyphenol oxidase (BsPPO), a synthesized Bsppo gene was cloned into the vector pMAL-c5x and expressed in E. coli. Subsequently, the MBP fusion label in the recombinant protein was removed by protease digestion after affinity purification. The synthesized Bsppo gene contained 1 752 bp which encodes 585 amino acids with a deduced molecular weight of 65.3 kDa. Transformation of the recombinant vector into E. coli BL21(DE3) resulted in soluble expression of the fusion protein MBP-BsPPO. The enzymatic properties of the recombinant BsPPO was investigated after MBP fusion tag excision followed by affinity purification. The results demonstrated that the optimal temperature and pH for BsPPO was 25°C and 4.0, respectively. BsPPO exhibited a good stability under low temperature and acidic environment. Low-intensity short-term light exposure increased the activity of BsPPO. Cu²⁺ could improve the activity of BsPPO while Zn²⁺ and Ca²⁺ showed the opposite effect. BsPPO could catalyze the oxidation of monophenols, diphenols, and triphenols, and exhibited good catalytic activity on l-tyrosine and vanillic acid. Moreover, BsPPO exhibited high catalytic activity on black sesame metabolites, including 2-methoxy cinnamic acid, indole-3-carboxylic acid and phloretin. These results may serve as a basis for further characterization of BsPPO.
Catechol Oxidase/genetics* ; Cloning, Molecular ; Escherichia coli/metabolism* ; Recombinant Proteins/genetics* ; Sesamum/genetics*

OBJECTIVETo study the relationship between fumonisin biosynthesis gene and toxicity of Fusarium moniliforme isolated in China.

METHODSThe toxigenic gene of 29 Fusarium moniliforme isolated from different provinces and varied food samples were determined. Eighteen fum5-positive strains were selected for biosyhesizing fumonisin and determined by high performance liquid chromatography (HPLC).

RESULTSTwenty-six isolates were identified as fum5 gene positive strains. And all of these strains produced FB(1), FB(2) and FB(3). The amount of FB(1), FB(2) and FB(3) was ranging from 0.41-140.20 mg/kg, 0.06-14.30 mg/kg to 0.30-58.00 mg/kg, except one strain produced a lower level of FB(1) only. It wight be the first report showing a high level fumonisin-producing strain isolated from the sesame sample and identified in the world. The amount of FB(1), FB(2) and FB(3) produced by the isolate was 128.84 mg/kg, 11.80 mg/kg and 14.88 mg/kg.

CONCLUSIONSIt should have a close relationship between fumonisins biosynthesis gene and toxicity of Fusarium moniliforme isolated in China. The study demonstrated that strain of Fusarium moniliforme might contaminate the sesame sample and produce a high level of fumonisins.

China ; Chromatography, High Pressure Liquid ; Food Contamination ; analysis ; prevention & control ; Fumonisins ; analysis ; metabolism ; Fungal Proteins ; genetics ; metabolism ; Fusarium ; genetics ; isolation & purification ; metabolism ; Sesamum ; microbiology