BIOSYNTHESIS OF PECTIC SUBSTANCES - LOCALISATION OF ENZYMES AND PRODUCTS IN A LIPID-MEMBRANE COMPLEX

1. 1. Further experiments on the biosynthesis of methylated pestic substances by a particulate preparation from mung bean shoots are reported. 2. 2. When the [14C]methyl-labelled pectin was generated in the preparation and the intact particles were incubated up to 2 h with high amounts of pectin methyl esterase, there was no loss of pectin methyl ester groups. They were, however, readily liberated after the addition of the detergents, sodium dodecyl sulphate and Triton X-100, or of phospholipase A. Under these conditions, the pectic substances as such remained bound to the particulate material. 3. 3. The liberation of pectin methyl ester groups under the influence of the above agents occurred, too, if no soluble esterase was added. This is due to an endogenous pectin methyl esterase which was shown by a sensitive new assay method to be present in the particulate enzyme preparation. Part of this endogenous esterase is soluble and part is bound to the particulate material. The effects of the endogenous and of added soluble esterase on the pectin are additive. Therefore, both seem to have the same mode of action on the particle-bound pectic substances. 4. 4. The results indicate that the biosynthesis of pectic substances proceeds in a structural compartment which contains the biosynthetic enzymes as well as their products. The complex is established by lipid membranes which keep the newly formed pectin and the esterase of the cells apart, as long as the integrity of the structure is not disturbed. © 1969.