Nitrate reductase was suggested to initiate nanoparticle formation by many fungi including Penicillium species, while several enzymes, α-NADPH-dependent reductases, nitrate-dependent reductases and an extracellular shuttle quinone, were implicated in silver nanoparticle synthesis for Fusarium oxysporum. Jain et al. (2011) indicated that silver nanoparticle synthesis for A. flavus occurs initially by a "33kDa" protein followed by a protein (cystein and free amine groups) electrostatic attraction which stabilizes the nanoparticle by forming a capping agent. Intracellular silver and gold nanoparticle synthesis is not fully understood but similar fungal cell wall surface electrostatic attraction, reduction, and accumulation has been proposed. External gold nanoparticle synthesis by P. chrysosporium was attributed to laccase, while intracellular gold nanoparticle synthesis was attributed to ligninase.