Expressed in many tissues with a relatively high level in skeletal muscle. The twin Cx9C motifs are involved in the recognition by the mitochondrial disulfide relay system. Overexpressed in T-cell leukemia bearing a t(X;14) translocation. Shares a non-coding 5' exon with isoform 2 which is spliced to a different set of 3' exons encoding an unrelated protein. Belongs to the CMC4 family. MTCP1 and MTCP1NB are transcribed from the same promoter and could be considered the same gene.