Functions as an activator of NOX1, a superoxide-producing NADPH oxidase. Functions in the production of reactive oxygen species (ROS) which participate in a variety of biological processes including host defense, hormone biosynthesis, oxygen sensing and signal transduction. May also activate CYBB/gp91phox and NOX3. {ECO:0000269|PubMed:12657628, ECO:0000269|PubMed:12716910, ECO:0000269|PubMed:14617635, ECO:0000269|PubMed:14978110, ECO:0000269|PubMed:15181005, ECO:0000269|PubMed:15824103, ECO:0000269|PubMed:17602954, ECO:0000269|PubMed:19755710}. This is the function of NOXA1 (NADPH oxidase activator 1, Ensembl gene identifier ENSG00000188747).