The bitter almond is slightly broader and shorter than the sweet almond and contains about 50% of the fixed oil that occurs in sweet almonds. It also contains the enzyme emulsin which, in the presence of water, acts on the two soluble glucosides amygdalin and prunasin yielding glucose, cyanide and the essential oil of bitter almonds, which is nearly pure benzaldehyde, the chemical causing the bitter flavor. Bitter almonds may yield 4–9 mg of hydrogen cyanide per almond and contain 42 times higher amounts of cyanide than the trace levels found in sweet almonds. The origin of cyanide content in bitter almonds is via the enzymatic hydrolysis of amygdalin. P450 monooxygenases are involved in the amygdalin biosynthetic pathway. A point mutation in a bHLH transcription factor prevents transcription of the two cytochrome P450 genes, resulting in the sweet kernel trait.