Chromophore/apoprotein interactions

We have used proteolytic enzymes to structurally alter isolated PSII reaction centres as a way of probing chromophore-apoprotein interactions. We have also used digestion of the reaction centre polypeptides in situ In the thylakoid membrane to examine herbicide binding in the Qg site. 

These conclusions are still consistent with the finding that significant conformational differences between Pr and Pfr do in fact exist ([65,147] for reviews see [8c, 148]). They can be rationalized—albeit not with conclusive rigour—by a conformational adaptation of the apoprotein part located around the bilatriene-binding pocket, following the Z E photoisomerization of the chromophore. This local change then should suffice to determine through bilatriene chromophore-protein interactions the spectroscopic characteristics of the chromophore as well as stability and reactivity of the two photochromic forms of phytochrome. 

In another paper, Liu et al. (30) described the interaction of hbronectin with heparin as a model system. The two distinct binding constants in the nanomolar range were derived from Scatchard plots and found in good agreement with published data. The established ACE binding assay was then applied to the molecular interaction of a kedarcidin chromophore with apoprotein. Dissociation constants in the lower micromolar range were calcu-... 

It is noteworthy that the quantum yield of the blue emitting chromophore in phytochrome, associated with human serum albumin [105], which corresponds to an increase of more than 20 times over the solution d>f values of the latter compounds. The similarity of the values suggests that the radiationless decay processes of the bilirubin-type chromophore are less efficient owing to interaction with the phytochrome apoprotein. 

L. Kappe, and I.G. Goldberg, Stabilization of neocarzinostatin nonprotein chromophore activity by interaction with apoprotein and with HeLa cells. Biochemistry, 19 (21), 4786-4790,1980. 

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