Involved in regulation of vitamin K-dependent carboxylation of multiple N-terminal glutamate residues. Seems to inhibit gamma-carboxylase GGCX. Binds 7 calcium ions with a low affinity (By similarity).
Subcellular locations: Endoplasmic reticulum membrane, Golgi apparatus, Secreted, Melanosome, Sarcoplasmic reticulum lumen