There are two human arylamine N-acetyltransferases
(NAT1 and NAT2) that have evolved separately and differ in their substrate
specificity and tissue localization. In addition to its acetyltransferase
activity, NAT1 can hydrolyze acetyl coenzyme A to coenzyme A in the
presence of folate. Here, we show that NAT1 is rapidly inactivated
at temperatures above 39 °C whereas NAT2 is more stable. NAT1
acetyltransferase activity is also rapidly lost in whole cells at
a rate similar to that of recombinant protein, suggesting it is not
protected by intracellular chaperones. By contrast, the hydrolase
activity of NAT1 is resistant to heat-induced inactivation, in part
because folate stabilizes the protein. Heat generated by mitochondria
following the dissipation of the inner membrane potential was sufficient
to inactivate NAT1 in whole cells. Within the physiological range
of core body temperatures (36.5–37.5 °C), NAT1 acetyltransferase
activity decreased by 30% while hydrolase activity increased by >50%.
This study demonstrates the thermal regulation of NAT1, but not NAT2,
and suggests that NAT1 may switch between an acetyltransferase and
a hydrolase within a narrow temperature range in the presence of folate
