Cyclic Activity of Enzymes of Asparagine-Pyruvate Pathway and Cellular Synchronization. Significance of L-Asparaginase Oscillatory States

Abstract

The periodic function of the asparagine-pyruvate pathway and that of the sporulation rhythm are strongly correlated in Leptosphaeria michotii. Indeed, conidiation rhythms are subtended by rhythms of metabolic activities having the same periodicity, which can operate without cell differentiation; asparagine-pyruvate pathway plays a main part in this periodic system: the activities of asparaginase, aspartate and alanine aminotransferases (AT) and the cellular aspartate pool express a 24 hour periodicity [1]. Sporulation rhythm is regulated by propargylglycine, a substrate analogue, specific for alanine AT in this fungus; it is, on the other hand, destabilized by cycloheximide. Furthermore, when asparaginase is the only enzyme of the pathway whose activity remains rhythmic, the sporulation rhythm pursues its course, but it is no longer regulated. When both activities of asparaginase and aspartate AT are rhythmic, sporulation rhythm is regulated. Alanine AT activity has also an influence on the function of the sporulation rhythm, but its activity could be still non-rhythmic. So, the synchronized working of the above three components of the asparagine-pyruvate pathway studied is necessary for the normal operation of the sporulation rhythm in L. michotii [2]. In this case, the control of the sporulation rhythm might be carried out through changes in the main metabolic pools driven by asparagine-pyruvate pathway.