PURIFICATION, CHARACTERIZATION, AND CDNA SEQUENCE OF GLUCOSE-6-PHOSPHATE-DEHYDROGENASE FROM POTATO (SOLANUM-TUBEROSUM L)

Abstract

Glucose-6-phosphate dehydrogenase (G6PDH, E.C. 1.1.1.49) has been purified from potato tuber at least 850-fold to apparent homogeneity as judged by SDS-PAGE. The enzyme was characterized by K-m values of 260 mu M for glucose-6-phosphate and 6 mu M for NADP and a broad pH optimum between pH 7.5 and 9. NADPH, GTP, ATP, acetyl CoA and CoA inhibited G6PDH activity. Dithiothreitol (DTT) did not inactivate the enzyme. A highly specific antiserum was produced in a rabbit and used for immunodetection of G6PDH in Western blots. A cDNA library from potato leaves was screened with DNA probes produced by the polymerase chain reaction (PCR) in the presence of g6pdh-specific primers. A full-length cDNA clone was analyzed and the derived amino acid sequence compared with known G6PDH sequences from various sources. The homology of the plant sequence with G6PDH sequences from animals and yeast was found to be rather high (52%), whereas there was significantly lower homology with sequences of bacterial origin (37%). The lack of a plastidic signal sequence as well as the insensitivity of the recombinant enzyme towards reduced DTT, support the view that the cDNA sequence of a redox-independent cytosolic isoform was obtained.