A monospecific antiserum to ferredoxin-NADP+-reductase inhibits the diaphorase activity of soluble ferredoxin-NADP+-reductase from chloroplasts. Two states of the molecular structure of the lamellar system have been observed, one of which is the state described earlier by Berzborn. Stroma-freed chloroplasts in this condition are not agglutinated by the antiserum, although a specific adsorption of antibodies to reductase onto the lamellar system was demonstrated by the Coombs test. However, a second type of chloroplast preparations gives direct agglutination upon addition of the antiserum. Apparently, agglutination in this state is not sterically hindered by neighboring protein structures. This type of chloroplast preparations appears swollen under the light micro scope, but exhibits high rates of electron transport.
Chloroplasts of three types of tobacco have been used which differ in the morphology of their lamellar systems. The green type contains a normal ratio of grana and intergrana regions whereas the other two types have extended intergrana regions with either only small grana or no partitions at all. Comparison of the maximal degree of inhibition of the NADP+-reduction in chloroplasts from these types of tobacco by the antiserum, leads to the conclusion that ferredoxin-NADP+-reductase is located in the grana and the intergrana regions of the lamellar system, in the outer surface of the thylakoid membrane.