Kleczkowski LA, Villand P, Olsen O-A
Hysteresis and reversible cold inactivation of ADP-glucose pyrophosphorylase from barley seed endosperm.
Zeitschrift für Naturforschung: 1993 48c:457-460
(AGP) from barley (Hordeum vulgare L.) seed endosperm showed a lag in
activity when assayed after storage at -20-degrees-C. The cold-stored
enzyme could regain most, or all, of its activity during 40-60 min
following exposure to ambient temperatures. The lags were not observed
when 2 mm MgCl2 was added to the storage buffer before freezing.
Storage at -20-degrees-C, in the absence of MgCl2, led to the
appearance of a low activity AGP form which was activated up to 3-fold
by 3-phosphoglycerate (PGA) and had high K(m) values with ATP of 0.3
and 1.2 mm (with and without PGA, respectively). In contrast, storage
at - 20-degrees-C in the presence of MgCl2 or incubation at +
20-degrees-C resulted in an active enzyme which was only weakly
activated by PGA (up to 30%) and had the respective K(m) values with
ATP of 0.1 and 0.3 mm. It is suggested that low temperature may induce
a change in the conformation and/or oligomerization state of the AGP
protein, resulting in a low activity enzyme form which has distinct
regulatory and kinetic properties.