Effects of trypsin treatment on the photochemical activity and polypeptide composition of the P700-chlorophyll a protein complex.

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Abstract
The P700-chlorophyll α protein complex purified from spinach consists of polypeptides of molecular mass 60-65, 23, 20, 17, 14, and 12kD. Proteolysis of the complex with trypsin for 24hr altered neither the photochemical activity of P700-chlorohyll α protein complex nor the characteristic effects of cations and pH on the electron transfer from plastocyanin to photooxidized P700. However, it was found that the trypsin-treated complex was photochemically inactive in the presence of 1% (v/v) Triton X-100, although 1% (v/v) Triton X-100 had no effect on the photochemical activity of the native complex. Upon lowering the concentration of Triton X-100 by dialysis, the digested complex regained the photochemical activity of P700. The results of SDS-polyacrylamide gel electrophoresis showed that proteolysis of the complex with trypsin for 24hr results in extensive degradation of polypeptides associated with this complex into small polypeptide fragments (M.W.≤14.000). Isolated reaction center protein (60-65kD polypeptide) was also treated with trypsin and we observed quite similar effects of trypsin treatment. All these data suggest that the structure of either trypsin digested P700-chlorophyll α protein complex or the reaction center protein required for its photochemical activity can be maintained through strong hydrophobic interactions among the nicked subunit polypeptides.

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