Inhibition or initiation of a radical polymerization reaction by an ultraviolet-induced enzymatic process.

alpha-Chymotrypsin was modified to a light-controllable enzyme derivative by acylating active serine 195 residue with a cinnamoyl group or analogue. Upon UV irradiation the acylgroup could be isomerized, leading to release of the inhibiting group. Enzymatic activity could thus be regulated by means of UV light. A full 100% inhibition of the enzymatic activity could not be reached by the cinnamoyl derivative. Only posttreatment with diisopropylfluorophosphate yields a fully inactive enzyme derivative. The shelf-life of the inhibited enzyme was rather poor. Only freeze-dried samples could be used for several months without significant recovery of activity. Adapting the sensitivity of the system to visible light seems limited to the size of an enzyme's active site. Combination of the enzymatic system producing an inhibitor or an initiator with a polymerization reaction can result in a photographic process with a higher amplification factor.