Together with bola2, acts as a cytosolic iron-sulfur (Fe-S) cluster assembly factor that facilitates [2Fe-2S] cluster insertion into a subset of cytosolic proteins (By similarity). Required for hemoglobin maturation (PubMed:23615448). Does not possess any thyoredoxin activity since it lacks the conserved motif that is essential for catalytic activity (By similarity). Homodimer; the homodimer is independent of 2Fe-2S clusters. Heterotrimer; forms a heterotrimeric complex composed by two bola2 molecules and one glrx3 molecule; linked by [2Fe-2S] clusters. The thioredoxin domain lacks the two redox-active cysteines. This strongly suggests that it lacks thioredoxin activity. Morpholino knockdown in embryos reducing the levels of grx3 protein to 40% severely impairs the synthesis of heme and the maturation of hemoglobin, and results in individuals with fewer red blood cells.