text: hCOX-1 had a specific activity of 18.8 mumol of O2/mg with a Km of 13.8 microM for arachidonate and Vmax. of 1500 nmol of O2/nmol of enzyme, whereas << hCOX-2 >> had a specific activity of 12.2 mumol of O2/mg with a Km of 8.7 microM for [[ arachidonate ]] and a Vmax. of 1090 nmol of O2/nmol of enzyme.