Comparison of the ADP-ribosylating thermozyme from Sulfolobus solfataricusand the mesophilic poly(ADP-ribose) polymerases

The poly(ADP-ribose) polymerase-like thermozyme purified from Sulfolobus so lfataricus was characterised with respect to some physicochemical propertie s. The archaeal protein exhibited a scarce electrophoretic mobility at both pH 2.9 and pH 7.5. Determination of the isoelectric point (pI = 7.0-7.2) a llowed us to understand the reason for the limited migration at pH 7.5, whi le amino acid composition analysis showed a moderate content of basic resid ues, which reduced mobility at pH 2.9. With respect to the charge, the arch aeal enzyme behaved differently from the eukaryotic thermolabile poly(ADP-r ibose) polymerase, described as a basic protein (pI=9.5). Well known inhibi tors of the mesophilic polymerase like Zn2+, nicotinamide and 3-aminobenzam ide exerted a smaller effect on the enzyme from S. solfataricus, reducing t he activity by at most 50%. Mg2+ was a positive effector, although in a dos e-dependent manner. It influenced the fluorescence spectrum of the archaeal protein, whereas NaCl had no effect. (C) 2000 Federation of European Micro biological Societies. Published by Elsevier Science B.V. All rights reserve d.