Temperature Dependence of O₂-Oscillation Pattern of Spinach Thylakoids

Abstract

Photosynthetic water cleavage into dioxygen and metabolically bound hydrogen in the form of plastohydroquinone takes place within a polypeptide complex referred to as system II (for details see ref.1). It is now widely assumed that a heterodimer of polypeptides D1 and D2 forms the matrix that carries the functional redox groups participating in the overall reaction sequence. Accordingly, this matrix determines the reaction coordinates of all individual redox steps. However, in addition to this protein matrix a number of polypeptides are associated that probably act as regulatory subunits. Furthermore, structural effects of functional relevance could also arise from the interaction of the proteins with the surrounding lipid environment of the membrane. Differential scanning calorimetry measurements (2) indicate, that in spinach thylakoids, five to ten per cent of the polar lipids undergo a phase transition in the temperature range of 10 to 30°C.