Isozyme analysis of human normal polymorphonuclear leukocyte phosphofructokinase

ROS and pentose phosphate pathway: mathematical modelling of the metabolic regulation in response to xenobiotic-induced oxidative stress and the proposed Impact of the gluconate shunt

Elevated intracellular levels of reactive oxygen species (ROS), e.g. resulting from exposure to xenobiotics, can cause severe damages. Antioxidant defence mechanisms, which involve regulation of enzyme activities, protect cells to a certain extent. Nevertheless, continuous or increased exposure can overwhelm this system resulting in an adverse cellular state. To simulate exposure scenarios and to investigate the transition to an adverse cellular state, a mathematical model for the dynamics of ROS in response to xenobiotic-induced oxidative stress has been developed. It is based on exposure experiments of human urothelial cells (RT4) to the nitrated polycyclic aromatic hydrocarbon 3-nitrobenzanthrone (3-NBA), a component of diesel engine exhaust, and takes into account the following metabolic pathways of the antioxidant defence system: glutathione redox cycle scavenging directly ROS, the pentose phosphate pathway and the gluconate shunt as NADPH supplier and the beginning of glycolysis. In addition, ROS generation due to the bioactivation of 3-NBA has been implemented. The regulation of enzyme activities plays an important role in the presented mathematical model. The in silico model consists of ordinary differential equations on the basis of enzyme kinetics and mass action for the metabolism of 3-NBA. Parameters are either estimated from performed in vitro experiments via least-squares fitting or obtained from the literature. The results underline the importance of the pentose phosphate pathway to cope with oxidative stress and suggest an important role of the gluconate shunt during low-dose exposure.

Analysis of phosphofructokinase subunits and isozymes in ascites tumor cells and its original tissue, murine mammary gland

Phosphofructokinase (PFK) subunits and isozymes have been examined in ascites tumor cells and murine mammary gland, the tissue from where this tumor originated. Ascites tumor was found to contain predominantly the C-type subunit, whereas the L-type subunit was more abundant in mammary gland. An altered M-type subunit of lower electrophoretic mobility was found in both cell types and no M4 homotetramers were detected in either of them. Characteristic regulatory properties of ascites tumor PFK, i.e. insensitivity to fructose-1,6-P2 activation and inhibition by P-enolpyruvate, were also observed in the mammary gland isozyme. The nature of these properties and the contribution of the distinct subunit types to fructose-1,6-P2 activation are discussed.