Monooxygenase that promotes depolymerization of F-actin by mediating oxidation of specific methionine residues on actin. Acts by modifying actin subunits at 'Met-44' and 'Met-47' through the addition of oxygen to form methionine-sulfoxide, leading to promote actin filament disassembly and prevent repolymerization. Plays a key role in semaphorin-plexin repulsive axon guidance and cell morphological changes, probably via its ability to modify and regulate actin. H(+) + L-methionyl-[F-actin] + NADPH + O2 = H2O + L-methionyl-(R)-S-oxide-[F-actin] + NADP(+) Interacts with plexA. Present in neuronal cell bodies, along axons, and in growth cones. Appears in the nervous system at stage 13 and labels motor and CNS projections, and at later embryonic stages, it is present on axons that make up all motor axon pathways: the intersegmental nerve (ISN), the intersegmental nerves b and d (ISNb and ISNd), and the segmental nerves a and c (SNa and SNc). Also present in segment boundaries at the position of muscle attachment sites and at low levels in the lateral cluster of chordotonal organs (at protein level). Localizes to growing bristle tips in close proximity to the bristle cell membrane and at sites of bristle branching and actin localization. Localizes to growth cones. During early development (stages 7-8), expressed in the ventral neurogenic region and in many nonneuronal tissues (including developing mesoderm, cells surrounding the cephalic furrow and amnioproctodeal invagination, and in gut primordia). This nonneuronal expression is also seen later in embryonic development (stages 11-17), where it is expressed within the anterior and posterior midgut primordia, the visceral musculature, and weakly in somatic musculature. During axonal pathfinding (stage 13 onward), expressed within the developing brain and ventral nerve cord in most, if not all, CNS neurons. Not highly expressed in peripheral sensory neurons. Directly regulated by Sox14 during pruning. Defects in motor neuron guidance, myofilament organization and bristle formation. Surviving adult flies show abnormally shaped bristle cell processes that are variously straight, thick, bent, twisted and/or had abnormal 'club-like' or blunt tips. Belongs to the Mical family. The reaction mechanism is subject to discussion. Some work suggest MICAL enzymes directly oxidize actin methionine residues to produce methionine-(R)-S-oxide. Other publications suggest that the enzyme functions as a NADPH oxidase producing H(2)O(2) (EC 1.6.3.1) and that it is the produced H(2)O(2) that is responsible for the methionine-(R)-S-oxide production.