The function of F13B (coagulation factor XIII B chain, Ensembl gene identifier ENSG00000143278) is as follows. The B chain of factor XIII is not catalytically active, but is thought to stabilize the A subunits and regulate the rate of transglutaminase formation by thrombin. {ECO:0000303|PubMed:21742792, ECO:0000303|PubMed:3021194}.