Dynamics of the Heat Stress Response of Ceramides with Different Fatty-Acyl Chain Lengths in Baker’s Yeast
Fig 2
Structure of the proposed model of ceramide dynamics.
Left panel: Detailed pathway of ceramide biosynthesis and utilization. The pathway consists of three major subsystems: synthesis and utilization of DHC (left column), synthesis and utilization of PHC (right column), and fatty acid elongation and desaturation (center column). V1, V6, V11, V16, V21, V26, V30, V34, V38 and V42 represent fluxes catalyzed by ceramide synthase. V3, V8, V13, V18, V23, and V28, V32, V36, V40 and V44 represent fluxes catalyzed by dihydroceramidase and phytoceramidase, respectively. Reactions exiting the system to the left or right, namely V5, V10, V15, V20, V25, V29, V33, V37, V41 and V45, represent fluxes catalyzed by IPC synthase, while reactions entering the system from the left or right, V2, V7, V12, V17, V22, V27, V31, V35, V39 and V43, represent fluxes catalyzed by IPCase (Isc1). V4, V9, V14, V19, V24 represent DHC hydroxylase. The vertically shown reactions represent reactions catalyzed by other enzymes, such as remodelase (V46), fatty acid elongases (V47, V48, V50, V51, V52, and V53), and desaturase (V49). The boxes marked “IPC” summarily account for the complex sphingolipids IPC, MIPC, and M(IP)2C and their inter-conversions. This simplification seems reasonable as all three, IPC, MIPC and M(IP)2C, can serve as sources for the production of DHC and PHC. Right panel: The dynamic flux estimation is partly based on some fluxes whose magnitudes we took from our previous model [13]. The table summarizes these fluxes and indicates on the right how they constrain fluxes in our present model.