Cystathionine-β-Synthase​

Cystathionine-β-synthase (EC 4.2.1.22, from Microorganism)

L-Homocysteine + L-Serine  ⇒  L-Cystathionine + H2O

The consumption of NADH is measured at 340nm by spectrophotometry.

UNIT DEFINITION

One unit (U) is defined as the amount of enzyme which consumes 1 μmol of NADH per min under the conditions described below.

REAGENTS PREPARATION

Reagent I: 50 mM pH 8.0 PBS, contains 10 mM L-Serine, 2 mM DL-Homocysteine, 0.38 mM S-adenosyl-methionine, 0.25 mM PLP, 1 mM DTT, 5 U/mL CBL, 0.2 mM NADH, 5 U/mL LDH. Enzyme diluent: 50 mM pH 8.0 PBS buffer. Sample: The enzyme was diluted to 0.8-2.4 U/mL with the enzyme diluent.

PROCEDURE

1. Add 1 mL Reagent I to the 1 mL cuvette and preheat it at 37℃ for 5 min.

2. Add 0.02 mL enzyme solution to the cuvette and mix.

3. Record the ΔAs at 340 nm in 1 minute in a spectrophotometer thermostated at 37℃. At the same time, measure the blank rate ΔAb by using the same method as the test except that the enzyme diluent is added instead of the enzyme solution.

This enzyme is useful for enzymatic determination of L-homocysteine when coupled with CBS and LDH in clinical analysis.