Extending the carbon chain: hydrocarbon formation catalyzed by vanadium/molybdenum nitrogenases

Abstract

In a small-scale reaction, vanadium-dependent nitrogenase has previously been shown to catalyze reductive catenation of carbon monoxide (CO) to ethylene, ethane, propylene, and propane. Here, we report the identification of additional hydrocarbon products [α-butylene, n-butane, and methane (CH(4))] in a scaled-up reaction featuring 20 milligrams of vanadium-iron protein, the catalytic component of vanadium nitrogenase. Additionally, we show that the more common molybdenum-dependent nitrogenase can generate the same hydrocarbons from CO, although CH(4) was not detected. The identification of CO as a substrate for both molybdenum- and vanadium-nitrogenases strengthens the hypothesis that CO reduction is an evolutionary relic of the function of the nitrogenase family. Moreover, the comparison between the CO-reducing capacities of the two nitrogenases suggests that the identity of heterometal at the active cofactor site affects the efficiency and product distribution of this reaction.

Fig. 1

Specific activities for individual product formation catalyzed by (A) V- and (B) Mo-nitrogenase and (C) comparison of total activities for hydrocarbon formation by the two nitrogenases in the presence of (1) H₂O or (2) D₂O. Legend: ➀ CH₄; ➁ C₂H₄; ➂ C₂H₆; ➃ C₃H₆; ➄ C₃H₈; ➅ α-C₄H₈; ➆ n-C₄H₁₀. Expanded scales of α-C₄H₈ and n-C₄H₁₀ formation are shown as insets. Specific activities were determined by quantitative GC analyses and calculated based on the formation of products (see Fig. S3) in the first 10 min of reaction (linear range). Data are presented as mean ± SD (N = 5).

Fig. 2

Distributions of hydrocarbons formed by (A) V- and (B) Mo-nitrogenases in the presence of (1) H₂O or (2) D₂O. The total amounts of hydrocarbons detected in V (A)- and Mo (B)-based reactions were set as 100%, respectively, and the percentages of individual products were determined accordingly for each nitrogenase. The alkene/alkane ratios of V- and Mo-nitrogenases are summarized in Table S1.