α -Man is widely distributed and diverse, and has been found in eukaryotic cytoplasm, endoplasmic reticulum, Golgi apparatus and lysosome. Different types and functions of α -Man are involved in the modification process of N-glycan.

α-man reacts with a specific substrate, and the product has a characteristic absorption peak at 406nm. The α-man activity can be calculated according to the rate of change of absorbance