 In particular, light, CO2 and O2 dependencies of isoprene emission are controlled by substrate availability, whereas temperature dependency of isoprene emission is regulated both by substrate level and enzyme activity.Isoprene is the most abundant hydrocarbon measurable in the breath of humans.The estimated production rate of isoprene in the human body is 0.15 µmol/(kg·h), equivalent to approximately 17 mg/day for a person weighing 70 kg.