MCD and Magnetization Studies of NifB/NifZ Minus Molybdenum Iron Protein from Azotobacter vinelandii

• Main Author: Cotton, Marcia S.
• Other Authors: Andrew W. Maverick
• Format: Others
• Language: en
• Published: LSU 2006
• Subjects: Chemistry
• Online Access: http://etd.lsu.edu/docs/available/etd-11162006-104012/

This study reports a characterization of the iron-sulfur clusters of the MoFe protein expressed by the nifBnifZ deletion strain of A. vinelandii. VT-MCD spectroscopic and magnetization analysis of as-isolated ΔnifBΔnifZ MoFe protein were undertaken. VT-MCD spectra of as-isolated ΔnifBΔnifZ MoFe protein contains bands remarkably similar to those seen in as-isolated ΔnifH MoFe protein, assigned to arise from an [4Fe-4S]⁺ cluster. The low-temperature magnetization curve of as-isolated ΔnifBΔnifZ MoFe protein reveals the MCD spectra bands stem from an S = ½ spin system with diamagnetic contributions of some other species. As-isolated ΔnifBΔnifZ MoFe protein is compared with as-isolated ΔnifH MoFe protein, which contains a P-cluster precursor, and the as-isolated ΔnifB MoFe protein, which contains a fully assembled P-cluster ([8Fe-7S)]. Using nonlinear regression, the experimental magnetization curve of as-isolated ΔnifBΔnifZ MoFe protein is compared and factored to contributions from as-isolated ΔnifH MoFe protein and as-isolated ΔnifB MoFe protein. The simulation suggests a 1:1 ratio of ΔnifH MoFe protein to ΔnifB MoFe protein. These results suggests the as-isolated ΔnifBΔnifZ MoFe protein has an αβ subunit pair that contains a P-cluster and the other αβ subunit pair contains a latent (defined as immature, or potential) P-cluster (two [4Fe-4S] or P-cluster precursor).