The susceptibility of the P‐benzoquinone‐mediated electron transport and atrazine binding to trypsin and its modification by CaCl2 in thylakoids and PS II membrane fragments

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Abstract
Comparative studies in thylakoids and oxygen‐evolving Triton X‐100 PS II membrane fragments reveal: (i) There exists one high‐affinity atrazine binding site per PS II in both preparations. The affinity is reduced in PS II membrane fragments, (ii) The susceptibility to tryptic attack on atrazine binding and p‐BQ‐mediated electron transport is markedly reduced by CaCl2 in PS II membrane fragments, but no protection is observed in thylakoids. NH2OH and K3[Fe(CN)6] both reduce the binding affinity in PS II membrane fragments. The action of NH2OH is invariant to CaCl2 addition. The implications of these findings for functional studies with PS II membrane fragments are discussed.