On one hand, calorie restriction turns on a gene called PNC1, which produces an enzyme that rids cells of nicotinamide, a small molecule similar to vitamin B3 that normally represses Sir2.

• 其一，热量限制会启动PNC1这个基因，制造清除细胞内菸碱醯胺（nicotinamide）的酵素，菸碱醯胺类似维生素B3，平常会抑制Sir2活性。