生物化学

Enzyme Kinetics assay of the WT

2025-05-06 生物化学加入收藏

Enzyme Kinetics assay of the WT To assay 17 b-HSD activity in lysates, cells wer

Enzyme Kinetics assay of the WT To assay 17 b-HSD activity in lysates, cells were harvested 48h after transfection using PBS Enzyme Free Cell Dissociation Solution ( specialty Media Inc., Lavellette, NJ), frozen on dry ice and stored at -80 C.

Cell pellets were thawed on ice, resuspended in :

* 10mM Tris-HCl(pH 7.4)/150mM KCL/1 mM EDTA/2mM Dithiothreitol (DTT) at protein concentration of 3-6 mg/ml , and snap-frozen on dry ice . After thawing at 37° C, the extracts were chilled on ice and sonicated for 30sec.

A typical assay for establish the apparent Vmax and Km of the Substrate ANDROST-4-ENE-3,17-DIONE of the normal & mutant HSD17B3 enzyme used:

* 20-30 microgram of total protein in 0.2 mL of 100mM Tris - citrate(pH6)/2mM DTT.

* Steroid substrate was added in different concent.(0.1-8 microM) , and NADPH was added to a final cocent. of 2mM.

* Reactions were initiated by the addition of enzyme and were carried out for 25’- 30’ min at 37 ° C .

A typical assay to establish the apparent pH of the normal & mutant HSD17B3 enzyme used:

* Serial variation of pH (range4.5pH -8.5pH), for the reaction Buffer : 100mM Tris -citrate/2mM DTT .

* Steroid substrate was added at final concent. of 5 mM ( where 1 mM were 14C- ANDROST-4-ENE-3,17-DIONE and 4mM were cold substrate).

Transfection of DNA into 293T cells by using LIPOFECTAMINE PLUS Reagent package (LIFE TECHNOLOGIES Cat.No.10964-013): Protocol

* The day before transfection, split and plating the cells, so the that they are 50%- 60% confluent the day of transfection. Avoid antibiotics at the time of transfection and during.

* Culture vessel:100mm

* plasmid DNA ; 4 microg * plasmid b-gal ; 1 microg

* PLUS reagent; 20 microliter

* LIPOFECTAMINE PLUS Reagent; 30 microliter

* Incubate at 37°C at 5% CO2 for 3h (see LIFE TECHNOLOGIES protocol.)

* After 3h inc., increase volume of medium to normal volume (see LIFE TECHNOLOGIES protocol.)

* The cell extract were assayed for reporter gene activity 48h after the start of transfection.