enzyme unit

enzyme unit

Non-SI unit
Name Symbol Quantity Expressed in terms of SI base units Expressed in terms of other SI units
enzyme unit U catalytic activity (160) × 10-6 s-1 mol ≈ 16.67 nkat


The enzyme unit, symbol U, is a non-SI unit of catalytic activity.

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 160 micromole of substrate per second, or approximately 16.67 nanomoles of substrate per second.

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Note: The enzyme unit has been superceded by the SI coherent derived unit the katal, symbol kat, and its subunits.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.