title: Distinct photorespiratory reactions are preferentially catalyzed by glutamate:glyoxylate and serine:glyoxylate aminotransferases in rice.
abstract: The metabolic function of glutamate:glyoxylate aminotransferase (GGAT) and serine:glyoxylate aminotransferase (SGAT) for photorespiration is still not exactly understood so far though it is mostly held that both enzymes may work in parallel in the reaction of glyoxylate to glycine during photorespiration of plants. Here, for the first time, we define the genes encoding GGAT and SGAT and report their biochemical and enzymatic properties in rice plants, in contrast to those from other plant species. Noticeably, GGAT exhibited approximately 18 fold higher catalytic efficiency (Kcat/Km) with glyoxylate and glutamate than SGAT with glyoxylate and serine, and additionally, rice leaves usually contain 3-4times higher abundance of glutamate relative to serine, implicating that GGAT may preferentially utilize glyoxylate to form glycine over SGAT. When SGAT or GGAT activity was regulated by gene transformation or nitrogen deficiency, respectively, it was observed that the glycine content was positively related to GGAT activities, while both serine and glycine contents were negatively related to SGAT activities. The results suggest that GGAT preferentially catalyzes the conversion of glyoxylate into glycine while SGAT is mainly responsible for the transamination reaction of serine to hydroxypyruvate in the photorespiratory pathway of rice.
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, South China Agricultural University, Guangzhou, China; Laboratory of Molecular Plant Physiology, College of Life Sciences, South China Agricultural University, Guangzhou, China; State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Zhisheng
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Institute of Rice Research, Guangdong Academy of Agricultural Sciences, Guangzhou, China.
authors.forename: Xingxue
authors.initials: X
authors.lastname: Mao
authors.affiliation: Laboratory of Molecular Plant Physiology, College of Life Sciences, South China Agricultural University, Guangzhou, China.
authors.forename: Juanying
authors.initials: J
authors.lastname: Ou
authors.affiliation: State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Nenghui
authors.initials: N
authors.lastname: Ye
authors.affiliation: State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Zhang
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, South China Agricultural University, Guangzhou, China; Laboratory of Molecular Plant Physiology, College of Life Sciences, South China Agricultural University, Guangzhou, China. Electronic address: xpeng@scau.edu.cn.
authors.forename: Xinxiang
authors.initials: X
authors.lastname: Peng
mesh_terms: D055162:Biocatalysis; D005998:Glycine / Q000737:chemistry / Q000378:metabolism; D006038:Glyoxylates / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D012275:Oryza / Q000201:enzymology*; D018515:Plant Leaves / Q000201:enzymology; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D000637:Transaminases / Q000235:genetics / Q000378:metabolism*
chemical_list: D006038:Glyoxylates; D011994:Recombinant Proteins; D012694:Serine; D000637:Transaminases; C023067:glyoxylate aminotransferase; C022636:serine-glyoxylate aminotransferase; C031150:glyoxylic acid; D005998:Glycine