Isolation and Some Properties of an Aminopeptidase from the Primary Leaf of Wheat (Triticum aestivum L.)

Evolution of nitrogen oxides (NO_(x), primarily as nitric oxide) from soybean (Glycine max L.] Merr.) leaves during purged in vivo nitrate reductase assays had been reported; however, these reports were based on a method that had been used for determination of NO_(x) in air. This method also detects other N compounds. Preliminary work led us to doubt that the evolved N was nitric oxide. Studies were undertaken to identify the N compound evolved from the in vivo assay that had been reported as NO_(x). Material for identification was obtained by cryogenic trapping and fractional distillation, and by chemical trapping procedures. Mass spectrometry, ultraviolet spectroscopy, and ¹⁵N-labeled nitrate were used to identify the compounds evolved and to determine whether these compounds were derived from nitrate. Acetaldehyde oxime was identified as the predominant N compound evolved and this compound is readily detected by the method for NO_(x) determination. Substantial quantities of acetaldehyde oxime (16.2 micromoles per gram fresh weight per hour) were evolved during the in vivo assay. Small amounts of nitrous oxide (0.63 micrograms N per gram fresh weight per hour) were evolved, but this compound is not detected as NO_(x). Acetaldehyde oxime and nitrous oxide were both produced as a result of nitrate (¹⁵NO₃⁻) reduction during the assay.