S-Linalool synthase activity in developing fruit of the columnar cactus koubo [Cereus peruvianus (L.) Miller]

Koubo [Cereus peruvianus (L.) Miller, Cactaceae] is a commercially grown columnar cactus that produces an apple-sized, berry-like, edible fruit. The unique aroma of this fruit is largely due to (S)-linalool and linalool derivatives. Cell-free extracts obtained from koubo fruits produced linalool from geranyl diphosphate (GDP) (apparent K _m 18 μM) in enzymatic assays containing the divalent ion cofactor Mn ²⁺ or Mg ²⁺. The predominant enantiomer produced in vitro was (S)-linalool, with an optical purity of 85%. Incubation of geranyl diphosphate in the presence of 1-10 mM FeSO ₄ or FeCl ₂, without added enzyme, supported the in vitro spontaneous formation of racemic linalool. The koubo linalool synthase displayed a molecular mass of 53 kDa as determined by gel permeation chromatography. Enzyme activity levels were negligible in green immature fruits and increased with fruit development and during storage, concomitant with the timing of linalool accumulation in fruits.