Читать книгу Plant Nucleotide Metabolism - Hiroshi Ashihara - Страница 75

Inosine/guanosine kinase (IGK, ATP: inosine/guanosine 5′-phosphotransferase, EC 2.7.1.73) catalyses the phosphorylation of inosine to IMP and that of guanosine to GMP using ATP as a phosphate donor. This enzyme activity was first found in cell-free extracts of Ehrlich ascites tumour cells (Pierre and LePage 1968). In contrast to AK, the occurrence of IGK is limited. Unusually, only a few prokaryotes, including E. coli and Salmonella typhimurium, contain IGK as opposed to AK activity (Nygaard 1983).

IGK has been detected in plants (Deng and Ashihara 2010; Katahira and Ashihara 2006) (Table 5.1). Partial purification of IGK from mitochondria of Jerusalem artichoke was reported by Combés et al. (1989) (Table 5.3). The enzyme appears to be located in the intermembrane space of mitochondria. The Km values for guanosine (14 μM) are lower than for inosine (70 μM). There are no reports of the plant IGK being cloned, but molecular studies with bacteria and animals indicate that AK and IGK belong to the ribokinase family of proteins that share a number of unique primary and tertiary structural elements (Park and Gupta 2008).