Several molecular species of<unk>  that vary in the length of the O-alkyl side-chain have been identified. * Its alkyl group is connected by an ether linkage at the C1 carbon to a 16-carbon chain. * The acyl group at the C2 carbon is an acetate unit (as opposed to a fatty acid) whose short length increases the solubility of<unk>  allowing it to function as a soluble signal messenger. * The C3 has a phosphocholine head group, just like standard phosphatidylcholine. Studies found that<unk>  could not be modified without losing its biological activity. Thus, small changes in the structure of<unk>  could render its signaling abilities inert. Investigation led to the understanding that<unk>  and blood pressure response were dependent on the sn-2 propionyl analog. If the sn-1 was removed then<unk>  lacked any sort of biological activity. Finally, the sn-3 position of<unk>  was experimented with by removing methyl groups sequentially. As more and more methyl groups were removed, biological activity diminished until it was eventually inactive.
Platelet-activating factor
Thrombin
Von Willebrand factor
Prothrombinase
Factor VIII 
Factor VIII
Kallikrein
Fibrinogen