enzyme unit

Non-SI unit

Name	Symbol	Quantity	SI units
enzyme unit	U	catalytic activity	(¹⁄₆₀) × 10^-6 kat
The enzyme unit, symbol U, is a non-SI unit of catalytic activity. The enzyme unit is not accepted for use with the SI. One enzyme unit is defined as the amount of catalytic activity of an enzyme that facilitates the conversion of one micromole of substrate per minute, under the specified conditions. One enzyme unit is equal to the catalytic activity of an enzyme that converts ¹⁄₆₀ micromole of substrate per second, or approximately 16.67 nanomoles of substrate per second.
Definition			Δν_Cs N_A^-1
$1 \mspace{4mu} \text{U} \mspace{6mu} = \dfrac{6.022 \mspace{4mu} 140 \mspace{4mu} 76 \times 10^{23}}{(6 \times 10^7)(9 \mspace{4mu} 192 \mspace{4mu} 631 \mspace{4mu} 770)} \mspace{6mu} \dfrac{\Delta \nu _{Cs}}{N_A}\\ \\ \\ 1 \mspace{4mu} \text{U} \mspace{6mu} \approx 1.091 \mspace{4mu} 841 \mspace{4mu} 979 \mspace{4mu} 292 \mspace{4mu} 799 \mspace{4mu} 049 \times10^{6} \mspace{6mu} \Delta \nu _{Cs} \mspace{4mu} {N_A}^{-1}$

The SI coherent derived unit of catalytic activity, the katal, is equal to the catalytic activity that converts one mole of substrate per second.

It follows that one enzyme unit is approximately equal to 16.67 nanokatals. 1 U ≈ 16.67 nkat.

$1 \mspace{4mu} \text{U} = 1 \mspace{4mu} \mu \text{mol} / \text{min}\\ \\ 1 \mspace{4mu} \text{U} = (1/60) \mspace{4mu} \mu \text{mol} / \text{s}\\ \\ 1 \mspace{4mu} \text{U} = (1000/60) \mspace{4mu} \text{nmol} / \text{s}\\ \\ 1 \mspace{4mu} \text{U} \approx 16.667 \mspace{4mu} \text{nkat}$

Note: The enzyme unit has been superceded by the SI coherent derived unit the katal, symbol kat, and its subunits. For catalytic activity in the order of 1 U, the nanokatal, symbol nkat, should be used.