The cell cycle in Helianthus tuberosus: analysis of polyamine-endogenous protein conjugates by transglutaminase-like activity

Parenchyma cells of dormant Helianthus tuberosus tubers were induced to enter a synchronous cell cycle with the aim of studying therein the modifications which proteins undergo when they bind to polyamines. A transglutaminase-like activity (TGase-like), which increases during the cell cycle, produces high molecular mass conjugates with [3H]- and [14C]-putrescine (PU) that can be precipitated with trichloroacetic acid or ammonium sulphate, together with complexes in which PU is not covalently bound. These pellets were subjected to acidic hydrolysis at high temperature and the amount of PU was determined by thin layer chromatography: PU decreases untill mid-G1 and then increases during the cell cycle, remaining stationary only at the beginning of cell division. Bound PU derivatives, especially compounds having a migration near zero, were also formed. Very low amounts of bound labelled spermidine, spermine or gamma aminobutyric acid were detected. The labelled conjugates that were not subjected to hydrolysis but analyzed by SDS-PAGE, were not mobile, and some of them could be separated by changing the percentage of acrylamide or by treating them with papain or cellulase and pectinase, suggesting that they are proteins linked to or entrapped by carbohydrates.