Iron-sulfur (Fe-S) clusters are prosthetic groups found in proteins, utilized in electron transfer and redox reactions. There are three specialized systems for Fe-S cluster biosynthesis: nitrogen fixation (Nif), iron sulfur cluster (Isc), and sulfur utilization factor (Suf). Suf system functions only in an iron limited and/or oxidative stress environment and encompasses six proteins, SufA, SufB, SufC, SufD, SufS, and SufE. The mechanism is unclear for how these proteins interact to form and transfer the Fe-S cluster to a target apo-enzyme. Surface Plasmon Resonance (SPR) provided insight into the interactions between the Suf proteins. SPR has confirmed a strong interaction between the cysteine desulfurase protein, SufS, and its sulfur transfer partner, SufE. SPR also shows that SufE further interacts with SufB to transfer sulfur to the SufBCD complex for Fe-S cluster assembly. In addition, with the aid of liquid chromatography electrospray ionization mass spectrometry we attempted to map the movement of sulfur within SufB. Sulfur is transferred from SufS to SufE and to SufB as a persulfide. However, it is unclear which of the thirteen cysteine (cys) residues found on SufB is the terminal acceptor at the actual site of cluster assembly.