| ADP-glucose pyrophosphorylase (ADPGlc PPase) from higher plants is a heterotetramer composed of two different subunits. The expression of a putative full-length cDNA encoding the small subunit of potato tuber ADPGlc PPase in Escherichia coli results in a catalytically active enzyme. Its specific activity is similar to that of the purified holoenzyme enzyme when assayed at a saturating concentration of activator. The activity of the large subunit is negligible. The homotetrameric small subunit differs from the heterotetrameric enzyme only in its regulatory properties. Thus, the small subunit is proposed to be mainly involved in catalysis, while the large subunit is mainly involved in modulating the regulatory properties of the small subunit. The N-terminus of the small subunit is most likely involved in the regulatory properties and heat stability of the holoenzyme since these properties were shown previously to be altered in a recombinant enzyme that contains the truncated small subunit (at the N-terminus) and the large subunit.;Lys;The catalytic activity of potato tuber enzyme is activated by a preincubation with ADP-glucose and dithiothreitol or by ATP, glucose-1-phosphate, Ca... |
