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. Author manuscript; available in PMC: 2010 Jun 15.
Published in final edited form as: Free Radic Biol Med. 2009 Mar 27;46(12):1626–1632. doi: 10.1016/j.freeradbiomed.2009.03.017

Figure 3. A–D. Influence of light on inhibition of purified, recombinant human NOS1 and NOS2 by methylcobalamin and adenosylcobalamin.

Figure 3

The effect of methylcobalamin (not exposed to light or exposed to light) and adenosylcobalamin (not exposed to light or exposed to light) on NOS1 (A and C) or NOS2 (B and D) activity is displayed. The agents were protected from light or exposed to light for 60 minutes. We performed the enzyme assays in near-dark conditions (as low light as possible). Results are expressed as percent inhibition. The effective dose for 50% inhibition (ED50) is displayed.

Light dissociates the methyl- or adenosyl- group from the agent resulting in hydroxocobalamin. Methylcobalamin and adenosylcobalamin have very little NOS inhibitory activity, but after light-induced change to hydroxocobalamin, they actively inhibit NOS1 and NOS2 activity.