Short-lived intermediate in N2O generation by P450 NO reductase captured by time-resolved IR spectroscopy and XFEL crystallography.

Nitric oxide (NO) reductase from the fungus Fusarium oxysporum is a P450-type enzyme (P450nor) that catalyzes the reduction of NO to nitrous oxide (N2O) in the global nitrogen cycle. In this enzymatic reaction, the heme-bound NO is activated by the direct hydride transfer from NADH to generate a short-lived intermediate ( I ), a key state to promote N-N bond formation and N-O bond cleavage. This study applied time-resolved (TR) techniques in conjunction with photolabile-caged NO to gain direct experimental results for the characterization of the coordination and electronic structures of I TR freeze-trap crystallography using an X-ray free electron laser (XFEL) reveals highly bent Fe-NO coordination in I , with an elongated Fe-NO bond length (Fe-NO = 1.91 Å, Fe-N-O = 138°) in the absence of NAD+ TR-infrared (IR) spectroscopy detects the formation of I with an N-O stretching frequency of 1,290 cm-1 upon hydride transfer from NADH to the Fe3+-NO enzyme via the dissociation of NAD+ from a transient state, with an N-O stretching of 1,330 cm-1 and a lifetime of ca. 16 ms. Quantum mechanics/molecular mechanics calculations, based on these crystallographic and IR spectroscopic results, demonstrate that the electronic structure of I is characterized by a singly protonated Fe3+-NHO•- radical. The current findings provide conclusive evidence for the N2O generation mechanism via a radical-radical coupling of the heme nitroxyl complex with the second NO molecule.

Effect of a rye B chromosome and its segments on homoeologous pairing in hybrids between common wheat and Aegilops variabilis.

Rye B chromosomes, which are supernumerary chromosomes dispensable for the host but increase in number by non-disjunction after meiosis, have been reported to affect meiotic homoeologous pairing in wheat-rye hybrids. The effect of a rye B chromosome (B) and its segments (B-9 and B-10) on homoeologous pairing was studied in hybrids between common wheat (2n=42) and Aegilops variabilis (2n=28), with reference to the Ph1 gene located on wheat chromosome 5B. The B-9 and B-10 chromosomes are derived from reciprocal translocations between a wheat and the B chromosomes, and the former had the B pericentromeric segment and the latter had the B distal segment. Both the B and B-9 chromosomes suppressed homoeologous pairing when chromosome 5B was absent. On the other hand, the B-9 and B-10 chromosomes promoted homoeologous pairing when 5B was present. On pairing suppression, B-9 had a greater effect in one dose than in two doses, and B-9 had a greater effect than B-10 had in one dose. These results suggested that the effect of the B chromosomes on homoeologous pairing was not confined to a specific region and that the intensity of the effect varied depending on the presence or absence of 5B and also on the segment and dose of the B chromosome. The mean chiasma frequency (10.23) in a hybrid (2n=36) possessing 5B and one B-9 was considerably higher than that (2.78) of a hybrid (2n=35) possessing 5B alone, and was comparable with that (14.09) of a hybrid (2n=34) lacking 5B. This fact suggested that the B chromosome or its segment can be used in introducing alien genes into wheat by inducing homoeologous pairing between wheat and alien chromosome.