Fate of the porphyrin cofactors during the light-dependent turnover of catalase and of the photosystem II reaction-center protein D1 in mature rye leaves

The apoprotein of the enzyme catalase (EC 1.11.1.6) was shown to exhibit a light-dependent turnover in leaves. Present results indicate that photoinactivation of the enzyme was not accompanied by a synchronous destruction and new synthesis of its heme moiety. In rye (Secale cereale L.) leaves the catalase content was not depleted in light when porphyrin synthesis was inhibited by gabaculine. Photoinactivation of purified bovine liver or rye leaf catalase in vitro was not accompanied by concomitant damage to the heme groups. Both the incorporation of delta-[H-3]aminolevulinic acid ([H-3]ALA) into catalase-heme and its apparent turnover increased with irradiance. However, the apparent half-life of the catalase-heme was much longer than that of its apoprotein. It is probable that not only degradation but also an exchange with the free heme pool contributed to the apparent turnover of radioactivity of the catalase-heme. Part of the chlorophyll (Ch1) associated with photosystem II (PS II) had a preferential light-induced turnover, and repair of PS II appeared to require new Ch1 synthesis also in mature green rye leaves. The activity of PS II, indicated by the ratio of variable to maximal fluorescence (F-v/F-m), rapidly declined in the presence of gabaculine in light and the reaction-center proteins D1 and D2 were depleted. When segments of mature green rye leaves were labeled with [H-3]ALA and incorporation into Ch1-protein complexes analysed after electrophoretic separation in the presence of Deriphat, the highest radioactivity was observed in the core complex of PS II, while PS I and the light-harvesting complex of PS II (LHC II) were unlabeled. In greening etiolated leaves highest incorporation was observed in LHC II. Both the incorporation of [H-3]ALA into the PS II core complex of green rye leaves and its turnover increased with irradiance. However, the apparent half-life of the PS II-bound labeled porphyrin compounds (mainly Ch1) was considerably longer than that of the reaction-center protein D1 under identical conditions.