Hydrolytic driving force. The hydrolysis of pyrophosphate to orthophosphate is i

Question

Hydrolytic driving force. The hydrolysis of pyrophosphate to orthophosphate is important in driving forward biosynthetic reactions such as the synthesis of DNA. This hydrolytic reaction is catalyzed in Escherichia coli by a pyrophosphatase that has a mass of 120 kDa and consists of six identical subunits. For this enzyme, a unit of activity is defined as the amount of enzyme that hydrolyzes 10 µ moles of pyrophosphate in 15 minutes at 37°C under standard assay conditions. The purified enzyme has a Vmax of 2800 units per millilgram of enzyme.
a. How many moles of substrate are hydrolyzed per second per milligram of enzyme when the substrate concentration is much greater than KM?

Explanation / Answer

Given definition: 1 U = 10 µmol PPi/15 min (for this enzyme) Given: Vmax = 2800 U/mg enzyme (2800 U/mg) x ((10umolPPi)/(15min/1U)) x (1min/60 sec)= 31.1 µmol PPi s-1 mg-1

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