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). Interacts with GGCX. Identified by mass spectrometry in melanosome fractions from stage I to stage IV. Ubiquitously expressed. Expressed at high levels in heart, placenta and skeletal muscle, at lower levels in lung, kidney and pancreas and at very low levels in brain and liver. Belongs to the CREC family.