Key Laboratory of South China Agricultural Plant Molecular Analysis and Genetic Improvement & Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Xingke Road 723, Tianhe District, Guangzhou 510650, China.
Key Laboratory of South China Agricultural Plant Molecular Analysis and Genetic Improvement & Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Xingke Road 723, Tianhe District, Guangzhou 510650, China; Center of Economic Botany, Core Botanical Gardens, Chinese Academy of Sciences, Xingke Road 723, Tianhe District, Guangzhou 510650, China.
Food Chem. 2020 Feb 1;305:125440. doi: 10.1016/j.foodchem.2019.125440. Epub 2019 Aug 30.
Tea (Camellia sinensis) contains two active glutamate decarboxylases (CsGADs), whose unclear properties were examined here. CsGAD1 was 4-fold higher than CsGAD2 in activity. Their K values for L-glutamate were around 5 mM. CsGAD1 and CsGAD2 performed best at 55 and 40 °C, respectively, and were both stimulated by calcium/calmodulin (Ca/CaM). Over 40 °C, their calmodulin-binding domains degraded. CsGADs were most active at pH 5.6, and were stimulated by Ca/CaM at pH 5.6-6.6, but inactivated at pH 3.6. Ca/CaM restored the CsGAD1 activity suppressed by inhibitors. CsGADs and CsCaM were localized to the cytosol. CsGAD1 was more highly expressed in most tissues, while CsGAD2 expression was more induced under stresses. The characteristics we first elucidated here revealed that CsGAD1 is the predominant isoform in tea plant, with CsGAD2 exhibiting a supplementary role under certain conditions. The information will contribute to regulation of GABA tea quality.
茶（茶树）含有两种活性谷氨酸脱羧酶（CsGADs），其性质尚不清楚。CsGAD1 的活性是 CsGAD2 的 4 倍。它们对 L-谷氨酸的 K 值约为 5mM。CsGAD1 和 CsGAD2 的最佳作用温度分别为 55°C 和 40°C，且均受钙/钙调蛋白（Ca/CaM）的刺激。超过 40°C 时，它们的钙调蛋白结合域降解。CsGADs 在 pH 5.6 时活性最高，在 pH 5.6-6.6 时受 Ca/CaM 刺激，但在 pH 3.6 时失活。Ca/CaM 恢复了抑制剂抑制的 CsGAD1 活性。CsGADs 和 CsCaM 定位于细胞质。CsGAD1 在大多数组织中的表达水平更高，而 CsGAD2 在应激下的表达水平更高。我们在这里首次阐明的特征表明，CsGAD1 是茶树中的主要同工型，而 CsGAD2 在某些条件下具有补充作用。这些信息将有助于 GABA 茶品质的调控。
