1-aminocyclopropane-1-carboxylate oxidase of apple fruit is periplasmic

Immunocytological studies have previously shown that 1-aminocyclopropane-1- carboxylate oxidase (ACO), the enzyme which catalyses the last step of ethy lene biosynthesis, is located in the cell wall of apple and tomato fruit ce lls. In the present study, a combination of cell fractionation and immunocy tological methods have been used in order to determine a precise location w ithin this space. Western blotting assays indicated that more than 70% of A CO antigens of the whole cell are recovered in freshly prepared protoplasts and that these ACO antigens are completely removed upon treatment of proto plasts with proteinase K. Immunocytolabelling showed a periplasmic AGO-anti gen signal in protoplasts which is completely absent in proteinase K-treate d protoplasts. Taken together, these data demonstrate that, in apple fruit, ACO is located at the external face of the plasma membrane. Possible inter actions between the plasma membrane and ACO activity are discussed.