부산대학교 도서관

5-Aminolevulinic acid for chlorophyll synthesis in greening barley is formed from glutamate. One of the steps involved in the conversion of glutamate to 5-aminolevulinic acid involves a reduction of glutamyl-tRNAGlu. to glutamate 1-semialdehyde and tRNAGlu. An enzyme catalysing this reduction was purified from the stroma of greening barley chloroplasts. An approximately 270-kDa protein composed of 54-kDa identical subunits was identified as the barley glutamyl-tRNAGlu reductase after purification by Sephacryl S-300, Cibacron Blue-Sepharose, 2'-5'-ADP-Sepharose, Mono S, Mini Q and Superose 12 chromatography. The sequence of 18 amino acids from the N-terminus of the reductase is 50% identical to a cDNA-deduced domain of the Arabidopsis thaliana hemA protein and encoded in a barley hemA cDNA sequence. This is an unequivocal demonstration that the glutamyl-tRNAGlu reductase subunit of higher plants is encoded in a hemA gene of the nuclear genome. Heme at 4 μM concentration or glutamate 1-semialdehyde at 200 μM caused a 50% inhibition of the reductase activity. Micromolar concentrations of Zn2+, Cu2+ and Cd2+ also inhibited barley glutamyl-tRNAGlu reductase. [ABSTRACT FROM AUTHOR]