During the asexual blood stage, initiates the proteolytic maturation of several rhoptry proteins and thus, is required for merozoite invasion of host erythrocytes and probably the subsequent development of the ring-stage (PubMed:29074775, PubMed:32109369). Cleaves rhoptry associated protein 1 RAP1 and apical sushi protein ASP during schizont maturation (PubMed:29074775, PubMed:32109369). Also cleaves rhoptry protein RON3 (PubMed:32109369). Inhibited by small molecule 49c (PubMed:29074775). Inhibited by small molecule WM382 (PubMed:32109369). In schizonts, localizes to the bulb of rhoptries. Expressed during the asexual blood stage, in schizonts and free merozoites (at protein level). Autocleaved into a p55 mature form. Normal asexual development in host erythrocytes (PubMed:29074775). Egress from erythrocytes is normal; however, subsequent erythrocyte invasion by newly released merozoites is severely impaired (PubMed:29074775). Accumulation of RAP1 p86 precursor resulting from impaired processing (PubMed:29074775). Impaired ASP processing (PubMed:29074775). Impaired secretion of CyRPA during merozoite egress from erythrocytes (PubMed:29074775). Belongs to the peptidase A1 family. It is unclear if PMIX is glycosylated as other members of the same enzyme family, i.e. PMI and PMII, are not.