Fig. 4. Effects of various SAM:SAH ratios on proteasome activity in purified preparations of A.

20S proteasome (representative experiment) and B. 20S proteasome vs IPr (immunoproteasome). 20S proteasome or IPr was incubated for 2h in buffers with varying SAM:SAH ratios and then proteasome activity was measured as detailed. * is p<0.05 difference in the activity between 20S proteasome and IPr and # is p<0.05 between control and other treatments (shown as % control, where the activity of both 20S proteasome and IPr in control was considered as 100%). C. Expression of methyl lysine in 20S proteasome under various SAM:SAH ratios. Purified 20S proteasome was incubated for 15 min in buffers with SAM:SAH ratio 5 or 2.5 and then immunoblotted and probed with antibody to methyl lysine. A 25kDa proteasome subunit showed positive reactivity with anti-methyl lysine. 1-no treatment; 2- treated with SAM:SAH ratio 5; 3-treated with SAM:SAH ratio 2.5.