Figure 1.

Pumping iron: hypothesized iron uptake mechanisms in schistosomes. Iron uptake at the schistosome tegument is proposed to occur via non-specific binding of the host iron-carrier protein, transferrin (Tf). Ferric (Fe³⁺) iron is cleaved from Tf and reduced to its ferrous (Fe²⁺) form by a ferric reductase. Ferrous iron is then transported by a divalent metal transporter (DMT1). The second hypothesized mode of iron acquisition uses haem. Haem is obtained as a by-product of blood-feeding from the breakdown of host erythrocytes by a haemoglobinolytic pathway. The resulting products from this are amino acids for nutrition, and haem. Hypothesized haem uptake is via a haem transporter in the gastrodermis. Haem is then catabolized by haem oxygenase to release the iron. Excess haem is sequestered in haematin and egested from the gut. Iron taken up by the helminth is stored in ferritin (Fer); Fer-1 in the vitelline cells of females and Fer-2 in general somatic tissues. Abbreviations: GC, gynecophoric canal.