The Elevation of Levels of Amyloplastic α-1,4-Glucan Phoaphorylase Protein in Cultured Cells of Acer pseudoplatanus during Sucrose Starvation

Abstract

Two types of α-1,4-glucan phoaphorylase isozyme were characterized in the suspension-cultured cells of sycamore (Acer pseudoplatanus). The type I, a major fraction of the total extractable phosphorylase, was shown to be localized in the cytoplasm and exhibited a hihg affinity towards glucans, whereas the low affinity type (type II) resided in the amyloplasts. These two isozymes were distinguishable in their immunological properties : the amyloplastic phosphorylase reacted strongly with the antibody raised against the potato tuber phophorylase, whereas the cytosolic enzyme did not rossed-react with the same antibody. Western blot anslysis revealed the molecular mass of the monomeric subunit of plastidic phosphorylase to be 10 kD. The amyloplastic phosphorylase activity and its protein contents increased about 5-fold during 45 hours of sucrose starvation, but significantly declined upon repleishment with sucrose, indicating a possible regulatory role of amyloplastic phosphorylase in breaking down the reserve starch stored in the amyloplast.