CD38 is a type II integral membrane receptor and adhesion molecule [ 28] and serves as a cytotoxic triggering molecule on natural killer cells [ 29].
Vitale, M. et al. Identification of NKp80, a novel triggering molecule expressed by human NK cells.
These are proteins whose amino acid sequences show the structural hallmarks of cell surface receptors but whose triggering molecules are as yet undiscovered.
It has been suggested that a loss in antioxidant capacity in plant tissues results in an intrinsic accumulation of H2O2, which could then act as a signalling molecule triggering lignification [5].
Then, in response to oxidative stress (one of the possible cause stimulating the development of scald) the α-farnesene may be auto-oxidized in CTols, which then act as a signaling molecule, triggering a defence mechanism based on antioxidant protection, carried out by an increased accumulation of polyphenolic compounds, in particular chlorogenic acid.
Experimental studies have established PACAP38 as a potent pharmacological "trigger" molecule of migraine-like attacks.
Chemokines are a superfamily of structurally homologous heparin-binding cytokine molecules that can promote immune responses and stem-cell survival, as well as triggering chemotaxis and angiogenesis [ 14].
The nonmetabolizable sucrose analog palatinose had a similar effect on OsSUT2 expression in rice embryos as sucrose, suggesting that sucrose acts as a direct molecule for triggering the up-regulation of OsSUT2 expression.
In the absence of a preexisting template that would assist the change, the involvement of a covalent modification, transient or irreversible and affecting either all or a minor subset of molecules, as a trigger was postulated and never discarded [9], [11].
In addition, mtROS also acts as a signaling molecule to trigger other inflammatory cytokines, such as TNF-α and IL-6 [ 50].
