The reaction with lactic acid as substrate is called forward reaction, and the reaction with pyruvic acid as substrate is called reverse reaction. The advantages of forward reaction are:

(1) The oxidized coenzyme I (NAD+) required by this method is more stable than the reduced coenzyme I (NADH) required by the reverse reaction, and it is easy to obtain pure products, with fewer impurities inhibiting LDH and lower price.

(2) Sodium lactate (or lithium lactate) substrate is more stable than pyruvate substrate;

(3) The inhibitory effect of excess lactic acid on LDH was lower than that of excess pyruvate.

Advantages of reverse reaction:

The dosage of (1)NADH is very small, and only 3% NAD+ is used for the forward reaction.

(2) The reaction rate of enzyme is faster than that of lactic acid method, and the absorbance changes greatly in unit time, so it can be determined in a short time with less samples;

(3) The linear relationship between enzyme activity and time is long;

(4) When the reaction is started with NADH or pyruvate, the reaction speed is the same, but in the reaction from lactic acid to pyruvate, the activity of LDH depends on the initiator used.