MICAL interacts with F-actin and uses NADPH as a cofactor to oxidize actin at Met44 and Met47 (b-actin nomenclature). Functionally, oxidation of Met44 has a profound effect on actin polymerization because the residue resides in the D-loop of subdomain 2 of the protein, which is critical for actin subunit contacts; thus, upon oxidation, Met44 becomes negatively charged and interferes with actin monomer-monomer interaction and promotes F-actin severing and depolymerization. Regulation of actin oxidation at Met44/Met47 has been shown to destabilize F-actin in vivo and to play a key role in a growing number of cellular processes.  As part of the MOXtrue? product line, Pyrene labeled rabbit skeletal muscle actin protein (MICAL-oxidized) (MXAP95) has been enzymatically oxidized at methionines 44 and 47  with the MICAL flavoprotein monoxygenase protein. Purified MICAL-oxidized (pyrene labeled) actin has reduced susceptibility to subtilisin A cleavage at M47/G48 by > 90%, and has also been validated for downstream applications such as actin polymerization assays.