[Isoform 1]: Lacks catalytic activity due to its inability to undergo the autocatalytic cleavage needed to produce a mature, enzymatically active heterodimer. {Experimental EvidencePubMed:23682772}. [Isoform 2]: Lacks catalytic activity due to its inability to undergo the autocatalytic cleavage needed to produce a mature, enzymatically active heterodimer. {Experimental EvidencePubMed:23682772}. [Isoform 3]: Lacks catalytic activity due to its inability to undergo the autocatalytic cleavage needed to produce a mature, enzymatically active heterodimer. {Experimental EvidencePubMed:23682772}.