Question

The kcat for the GTP hydrolysis by the G? subunit of a heterotrimeric G protein is 0.026 /min How long will a single molecule of G? be active?

Answer 1

K_cat represents the turn over number of a enzyme. Turn over is the number of substrate molecules that are converted to the product per second for a given enzymatic concentaration.

The number of GTP molecules that are converted to the GDP per minute is 0.026.

0.026 GTP molecules remain bind with the enzyme for 1 minute.

1 GTP molecule remains bind with the enzyme = 1/0.026 = 38.46 minutes.

The G protein remains active until the GTP is hydrolysed to GDP. Before hydrolysis, the GTP molecule remains bind with the enzyme for 38.46 minutes. So the single G molecule remains active for 38.46 minutes.