All are second messengers except:
Remember that guanylyl cyclase is an enzyme while cGMP is a secondary messenger
Types of second messengers
There are 3 basic types of secondary messenger molecules:
1. Hydrophobic

DAG
IP3
Phosphotidylinositol

2. Hydrophilic

cAMP
cGMP

3. Gases

NO
CO
Cyclic AMP
Guanylyl cyclase
Diacylglycerol
Inositol triphosphate