Cho M H, Hahn T R
Department of Genetic Engineering and Plant Metabolism Research Center, Kyung Hee University, Suwon, Korea.
Arch Biochem Biophys. 2000 Oct 15;382(2):238-44. doi: 10.1006/abbi.2000.1984.
Carthamin, a red quinochalcone pigment in safflower (Carthamus tinctorius L.), is enzymatically converted from a yellow precursor, precarthamin. The enzyme, which catalyzes the oxidative decarboxylation of precarthamin to carthamin, was purified to apparent homogeneity from yellow petals of safflower and named precarthamin decarboxylase. The molecular mass of the denatured enzyme was estimated as 33 kDa by SDS-PAGE. The molecular mass of the native enzyme was determined by gel filtration chromatography to be 24 kDa; thus, the native enzyme is a monomer. The optimum pH of the enzyme was 5.0. The enzyme activity was inhibited by Mn2+, Fe2+, and Cu2+ and sharply decreased at temperatures higher than 50 degrees C for 10 min. The activation energy and the Arrhenius frequency factor of the enzyme reaction were 19.7 kcal mol(-1) and 9.94 x 10(11) s(-1), respectively. The saturation curve of precarthamin showed that the enzyme follows Michaelis-Menten kinetics. The Km and Vmax of the enzyme were calculated as 164 microM and 29.2 nmol/ min, respectively. The turnover number (kcat) of the enzyme was calculated as 1.42 x 10(2) s(-1). The enzyme activity was severely inhibited by reducing agents such as glutathione and DTT at pH 5.0, suggesting that a disulfide bond may play an important role in enzyme function.
红花苷是红花（Carthamus tinctorius L.）中的一种红色醌查尔酮色素，由黄色前体物质前红花苷经酶促转化而成。将催化前红花苷氧化脱羧生成红花苷的酶从红花黄色花瓣中纯化至表观纯一，并命名为前红花苷脱羧酶。经SDS - PAGE测定，变性酶的分子量估计为33 kDa。通过凝胶过滤色谱法测定天然酶的分子量为24 kDa；因此，天然酶是单体。该酶的最适pH为5.0。酶活性受到Mn2 +、Fe2 +和Cu2 +的抑制，在高于50℃的温度下保温10分钟酶活性急剧下降。酶反应的活化能和阿仑尼乌斯频率因子分别为19.7 kcal mol(-1)和9.94 x 10(11) s(-1)。前红花苷的饱和曲线表明该酶遵循米氏动力学。该酶的Km和Vmax分别计算为164 microM和29.2 nmol/ min。该酶的转换数（kcat）计算为1.42 x 10(2) s(-1)。在pH 5.0时，该酶的活性受到谷胱甘肽和二硫苏糖醇等还原剂的严重抑制，这表明二硫键可能在酶的功能中起重要作用。
