79943-68-3 HHAP Hydra growth activator Hydra head activator peptide Peptide (hydra head-activator) Peptide head activator Peptide hydra morphogen Pglu-pro-pro-gly-gly-ser-lys-val-ile-leu-phe Pyroglutamyl-prolyl-prolyl-glycyl-glycyl-seryl-lysyl-valyl-isoleucyl-leucyl-phenylalanine head activator peptide