# Administrative Supplement for Equipment > **NIH NIH R01** · MASSACHUSETTS INSTITUTE OF TECHNOLOGY · 2024 · $142,176 ## Abstract Research Strategy Summary of Parent Award: Enzymes with complex metallocofactors in their active sites catalyze myriad transformations relevant to human health and disease. Understanding their reaction mechanisms requires molecular-level characterization of their resting states and intermediate states, and metal-specific spectroscopic techniques are especially useful in this endeavor. However, the high nuclearity of many metallocofactors can limit the usefulness of such techniques; the signals arising from multiple metal sites can be challenging to resolve, especially in mixtures of reaction intermediates. Moreover, it is often impossible to map the rich spectroscopic information onto the geometric structure, and this severely limits our understanding of the chemical bonding—and therefore the reactivity—of complex metallocofactors. We propose to address these challenges by developing methods for modifying the isotopic and elemental compositions of complex metallocofactors, in particular the nitrogenase catalytic cofactors. Nitrogenases are responsible for supplying a significant portion of the fixed nitrogen on the planet, and they therefore play an important role in maintaining a healthy and growing human population. Their catalytic cofactors are among the most complex in Nature, and as a result their reaction mechanisms have been especially difficult to characterize. To overcome these challenges and gain new insights into the mechanism of biological nitrogen fixation, we will develop chemical methods for precisely altering the isotopic and elemental composition of nitrogenase cofactors. Our approach is to discover mild protocols for removing specific Fe sites in nitrogenase cofactors and subsequently replacing them with 57Fe. The site-selectivity of the label will allow for the electronic structure (as elucidated spectroscopically) to be connected to the geometric structure (as defined crystallographically), and will thereby provide unprecedented insights into the chemical bonding and reactivity of nitrogenase cofactors. Studies of these cofactors in both their resting states and intermediate states comprise the heart of the proposal. We will also extend the site- selective 57Fe labeling protocol to incorporating different metals into specific sites of nitrogenase cofactors. This will yield artificial metalloenzymes that will serve as mechanistic probes with potentially unique properties and/or reactivity. Completion of this project will provide unprecedented mechanistic insights into biological nitrogen fixation and will articulate concepts and protocols for rendering complex metallocofactors as mechanistically tractable as mononuclear active sites. Justification for proposed equipment: The proposed modern ultracentrifuge would replace our current ultracentrifuge (a decades-old Beckman Coulter L70, heretofore referred to as the “Old Ultracentrifuge”), which was listed in the Equipment section of our grant proposal submitted in 2021. We first d... ## Key facts - **NIH application ID:** 11098351 - **Project number:** 3R01GM145787-03S1 - **Recipient organization:** MASSACHUSETTS INSTITUTE OF TECHNOLOGY - **Principal Investigator:** Daniel Leif Migdow Suess - **Activity code:** R01 (R01, R21, SBIR, etc.) - **Funding institute:** NIH - **Fiscal year:** 2024 - **Award amount:** $142,176 - **Award type:** 3 - **Project period:** 2022-04-01 → 2025-04-30 ## Primary source NIH RePORTER: https://reporter.nih.gov/project-details/11098351 ## Citation > US National Institutes of Health, RePORTER application 11098351, Administrative Supplement for Equipment (3R01GM145787-03S1). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/11098351. Licensed CC0. --- *[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*