Significant increase in the activity of an
acetyl-CoA hydrolase (
ATP-stimulated,
ADP-inhibited
enzyme) in the supernatant fraction of rat liver was observed after 44-68 h of
starvation (about 2-fold), and in the early stage of diabetes (about 1.6-fold), but not in the chronic stage of diabetes. The increased enzymatic activity in starved rats returned to the control level within 20 h when the animals were given laboratory chow, but not when they were given
fat-free diet with a high
carbohydrate content, and the
enzyme activity was increased by the latter diet containing 1% thyroid
powder. A single
intraperitoneal injection of 3,3'5-triiodo-L-thyronine or 3,3',5,5'-tetraiodo-L-thyronine resulted in twice the normal
enzyme activity two days later, and conversely 7 days after
thyroidectomy, the
enzyme activity was about 60% of the control level. A single
subcutaneous injection of alpha-(p-chlorophenoxy)
isobutyric acid, a
hypolipidemic drug, doubled the
enzyme activity in euthyroid rats, but not in thyroidectomized rats. Of the various tissues tested besides the liver, only the kidney had detectable
ATP-stimulated and
ADP-inhibited
enzyme activity (5% of the activity in liver cytosol). The kidney
enzyme had similar kinetic and immunochemical properties to the liver
enzyme. Changes in the
enzyme activity in the liver in various states were closely related to the amount of
enzyme present, judging from results obtained by
enzyme-linked
immunosorbent assay. The physiological role of this
enzyme (which hydrolyzes
acetyl-CoA to
acetate and
CoASH) may be in maintenance of the cytosolic
acetyl-CoA concentration and
CoASH pool for both
fatty acid synthesis and oxidation.