This domain is found in plant proteins such as respiratory burst NADPH oxidase proteins which produce reactive oxygen species as a defence mechanism. It tends to occur to the N-terminus of an EF-hand (Pfam:PF00036), which suggests a direct regulatory effect of Ca2+ on the activity of the NADPH oxidase in plants [1].

1: Six Arabidopsis thaliana homologues of the human respiratory burst oxidase (gp91phox). Torres MA, Onouchi H, Hamada S, Machida C, Hammond-Kosack KE, Jones JD; Plant J 1998;14:365-370. PMID:9628030