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Figure 4: Protection of enzyme activity with compatible solutes. The restriction enzyme DdeI was irradiated up to 5 kGy in the presence or absence of oxygen, in water or with the addition of 20 mM MG, 20 mM MG and 0.025 mM Mn, 20 mM DIP, or 20 mM MG, 20 mM DIP, and 0.025 mM Mn. The 20 mM solution of DIP had a pH of 9.5; thus 10 mM  PiB was added for a final pH of 7.5. Residual restriction enzyme activity was assayed by the digestion of pUC19 plasmid DNA; fragments were analyzed by agarose gel electrophoresis. The first lanes are molecular size ladders.