During the asexual blood stage, catalyzes the cleavage of denatured host hemoglobin (Hb) or globins (PubMed:11782538, PubMed:16452306). Digestion of host Hb is an essential step which provides the parasite with amino acids for protein synthesis, and regulates osmolarity (Probable). Hydrolysis of the bonds linking certain hydrophobic residues in hemoglobin or globin. Also cleaves small molecules substrates such as Ala-Leu-Glu-Arg-Thr-Phe-|-Phe(NO2)-Ser-Phe-Pro-Thr. Inhibited by pepstatin A. Optimum pH is 5.4. Component of the hemozoin formation complex (HFC) composed of falcipain 2, plasmepsins PMII, PMIII/HAP and PMIV, heme detoxifying protein HDP and falcilysin FLN. The HFC complex is involved in hemoglobin degradation and detoxification of heme in the food vacuole during the asexual blood stage. In trophozoites, localizes to the digestive (or food) vacuole, an acidic vacuole where host hemoglobin is digested. Expressed during the asexual blood stage; expression begins in mid to late trophozoites and continues in schizonts (at protein level). Proteolytically cleaved into the soluble active mature form by cysteine proteases in the digestive vacuole of trophozoites (Probable). Proteolysis requires an acidic environment (Probable) (PubMed:16452306). Autoprocessing or transprocessing by other plasmepsins such as PMII may serve as an alternate activation system (PubMed:16452306). Belongs to the peptidase A1 family. It is unclear if PMIV is glycosylated as other members of the same enzyme family, ie. PMI and PMII, are not.