Hydrolytic driving force. The hydrolysis of pyrophosphate to orthophosphate is important in driving forwards biosynthetic reactions such as the synthesis of DNA. THis hydrolytic reaction is catalyzed in E. coli by a pyrophosphatase that has a mass of 120 kd and consists of 6 identical subunits. For this enzyme, a unit of activity is defined as the amount of enzyme that hydrolyzes 10µmol of pyrophosphate in 15min at 37degrees celsius under std assay conditions. The purified enzyme has a Vmax of 2800 units per milligram of enzyme.
(a)How many moles of substrate are hydrolyzed persecond per milligram of enzyme when the substrate conc is much greater than KM?
(b)How many moles of active sites are there in 1mg of enzyme? Assume that each subunit has one active site.
(c)What's the turnover number of the enzyme? Compare this value with others mentioned in this chapter.