Intracellular NADPH Levels Affect the Oligomeric State of the Glucose 6-Phosphate Dehydrogenase

Abstract

In the yeast Kluyveromyces lactis, glucose 6-phosphate dehydrogenase (G6PDH) is detected as two differently migrating forms on native polyacrylamide gels. The pivotal metabolic role of G6PDH in K. lactis led us to investigate the mechanism controlling the two activities in respiratory and fermentative mutant strains. An extensive analysis of these mutants showed that the NAD ؉ (H)/NADP ؉ (H)-dependent cytosolic alcohol (ADH) and aldehyde (ALD) dehydrogenase balance affects the expression of the G6PDH activity pattern. Under fermentative/ethanol growth conditions, the concomitant activation of ADH and ALD activities led to cytosolic accumulation of NADPH, triggering an alteration in the oligomeric state of the G6PDH caused by displacement/release of the structural NADP ؉ bound to each subunit of the enzyme. The new oligomeric G6PDH form with fastermigrating properties increases as a consequence of intracellular redox unbalance/NADPH accumulation, which inhibits G6PDH activity in vivo. The appearance of a new G6PDH-specific activity band, following incubation of Saccharomyces cerevisiae and human cellular extracts with NADP ؉ , also suggests that a regulatory mechanism of this activity through NADPH accumulation is highly conserved among eukaryotes.

Glucose 6-phosphate and alcohol dehydrogenase activities are components of dynamic macromolecular depots structures

“…The appearance of the I G6PDH band is strictly correlated to the intracellular accumulation of NAD(P)H [17]. In contrast, when the S. cerevisiae cellular extracts were run and stained for G6PDH activity in native PAGE, they showed only one band, independently of growth conditions, (Fig.…”

“…1, lane 4), two bands when cells were grown in fermentative conditions or in the presence of ethanol (Fig. 1, lane 3) and many bands (lane 5) when the same strain was transformed with the plasmid containing the wild type ZWF1 gene, coding for the G6PDH, fused to the GFP gene [17].…”

Enhancement of Simultaneous Xylose and Glucose Utilization by Regulating ZWF1 and PGI1 in Saccharomyces Cerevisiae

“…G6PDH is a component of dynamic macromolecular depot structures in S. cerevisiae. The oligomeric state of G6PDH is affected by intracellular NADPH levels; G6PDH activity is under strong feedback inhibition by NADPH [40,41]. In addition, NADPH is a product of G6PDH.…”

Underinvestigated Roles of Glucose-6-Phosphate Dehydrogenase

“…It was found that G6PDH was allosterically regulated by NADPH/NADP + ratio [56,67] and sterols [59,67]. In coldblooded animals, G6PDH was shown to be reversibly phosphorylated/dephosphorylated [70].…”