Stabilization of heat-induced changes in plant peroxidase preparations by clpx, a bacterial heat shock protein

Peroxidases (PODs) are known to be quite stable at elevated temperatures.
Moreover, partially denatured peroxidases are able to regain their
catalytic activity during incubation at room temperature. In this paper,
we describe the effects of some heat shock proteins on the self-
reactivation of plant peroxidase preparations. Horseradish and artichoke
peroxidases (HRP and ARP, respectively) were first heated (at 60°C or 90°
C), then incubated at a slightly elevated temperature (30°C). The heat-
treatment resulted in a considerable loss of activity of both enzymes but
the subsequent incubation allowed their reactivation. However, no
reactivation could be detected when incubation was carried out in the
presence of the molecular chaperone ClpX. Other chaperones that were
tested (DnaK, DnaJ and GrpE) did not show the inhibitory effect.
Electrophoretic analyses further indicated that the heat-treated
horseradish peroxidase, but not the native enzyme, binds to Clpx
eliminating the possibility of undesirable protein refolding that would
result in aggregation.