Module 2: Figure cADPR/NAADP function
Synthesis and mode of action of cADPR and NAADP.
The enzyme ADP-ribosyl cyclase is a bifunctional enzyme that has a synthase (S) component that synthesizes cADPR and NAADP from the precursors NAD+ and NADP respectively, but it also has a hydrolase (H) activity that converts cADPR into ADPR. This hydrolase is sensitive to metabolism because it is inhibited by either ATP or NADH. The cADPR may act by stimulating the sarco/endo-plasmic reticulum Ca2+-ATPase (SERCA) pump to increase the uptake of Ca2+ into the endoplasmic reticulum. NAADP acts on a channel to release Ca2+ from a lysosome-related organelle.