The formation of the phosphorylase ab hybrid and its further transformation into phosphorylase a has been demonstrated in the rat heart after different periods of i.v. isoproterenol administration. Phosphorylase ab hybrid was determined in the presence of AMP and/or caffeine. Only the partially phosphorylated phosphorylase was found in the control rat hearts and its activity was 30 % of the total phosphorylase. The phosphorylase ab hybrid was disclosed particularly after small isoproterenol doses (0.031 -0.062 /rg.kg-1) and at short time interval (15 s) after its administration. Higher isoproterenol doses (0.25-0.5 ¿/g.kg-1) changed the partially phosphorylated phosphorylase to phosphorylase a (58 %) after a longer time interval (40 s), The phosphorylase ab hybrid was revealed even at the maximal rate of stimulation. The formation of the phosphorylase ab hybrid in the rat heart in vivo appears to be of physiological significance. Our results confirmed the earlier suggestion that the -AMP/-f AMP activity ratio reflects the percentage proportion of the phosphorylated subunits of phosphorylase but not of the activated phosphorylase molecules.
The protective role of light-harvesting complex 2 (LHC2) dissociation from photosystem 2 (PS2) complex was explored by the 5'-p-fluorosulfonylbenzoyl adenosine (FSBA, an inhibitor of protein kinase) treatment at saturating irradiance (SI) in soybean leaves and thylakoids. The dissociation of some LHC2s from PS2 complex occurred after SI treatment, but FSBA treatment inhibited the dissociation as demonstrated by analysis of sucrose density gradient centrifugation of thylakoid preparation and low-temperature (77 K) chlorophyll (Chl) fluorescence. A significant increase in F0 and decrease in Fv/Fm occurred after SI, and the two parameters could largely recover to the levels of dark-adapted leaves after subsequent 3 h in the dark, but they could not recover in the FSBA-treated leaves at SI. Neither the electron transport activity of PS2 nor the D1 protein amount in vivo had significant change after SI without FSBA, whereas FSBA treatment at SI could result in significant decreases in both the PS2 electron transport activity and the D1 protein amount. When thylakoids instead of leaves were used, the PS2 electron transport activity and the D1 protein amount declined more after SI with FSBA than without FSBA. The phosphorylation level of PS2 core proteins increased, while the phosphorylation level of LHC2 proteins was reduced after SI. Also, the phosphorylation of PS2 core proteins could be greatly inhibited by the FSBA treatment at SI. Hence in soybean leaf the LHC2 dissociation is an effective strategy protecting PS2 reaction centres against over-excitation and photodamage by reducing the amount of photons transferred to the centres under SI, and the phosphorylation of PS2 core proteins plays an important role in the dissociation. and Hai-Bo Zhang, Da-Quan Xu.