Abstract
Actin polymerisation and depolymerisation is a key process for the motile behaviour of cells including locomotion, generation of cell shape, volume regulation or responses to local stimulations. In addition to actin a variety of actin binding proteins is involved in these processes. Besides the ‘classical’ binding proteins (e.g. hymosin ß4, profilin, arp etc.) glycolytic enzymes may play a major role in the control of polymerisation, bundling and stiffness of actin fibrils. These actions are in addition to their role in energy metabolism which also is strongly related to their association with cytoskeletal elements providing the ATP driving cytoplasmic contractions. Using an oscillating rod rheometer based on a phase – sensitive acoustic microscope operated at 1 GHz, polymerisation kinetics of alpha- and of beta-actin in the presence of profilin, aldolase and LDH have been investigated. Mutual alterations of enzyme activity and polymerisation kinetics underline the specificity of the interaction and the functional significance. E.g. aldolase stimulates polymerisation in presence of its substrate while it inhibits filament formation without fructose-bisphosphate. Some structural consequences of these interactions were analysed by electron microscopy. The functional significance of the associations of the glycolytic enzymes with the actin fibrils for cell motility was revealed by induction of movement or of contraction in permeabilised cells fed with fructose-bisphosphate and by reduction of lamella propagation and amount of polymerised actin at the leading edge after inhibition of LDH using oxamic acid.