N. Mostafa et al., SEASONAL-CHANGES IN CRITICAL ENZYMES OF LIPOGENESIS AND TRIACYLGLYCEROL SYNTHESIS IN THE MARMOT (MARMOTA-FLAVIVENTRIS), Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 163(6), 1993, pp. 463-469
Fatty acid metabolism and triacylglycerol synthesis are critical proce
sses for the survival of hibernating mammals that undergo a prolonged
fasting period. Fatty acid synthase, fatty-acid-CoA ligase, diacylglyc
erol acyltransferase, and monoacylglycerol acyltransferase activities
were measured in liver and in white and brown adipose tissue, in order
to determine whether enzymes of lipogenesis and triacylglycerol synth
esis vary seasonally during hibernation in the yellow-bellied marmot (
Marmota flaviventris). Compared with mid-winter hibernation, fatty aci
d synthase activity was higher in all three tissues during early sprin
g when marmots emerged from hibernation and in mid-summer when they we
re feeding, consistent with the synthesis of fatty acids from the carb
ohydrate-rich summer diet. Fatty-acid-CoA ligase and diacylglycerol ac
yltransferase activities were highest in summer in white adipose tissu
e when triacylglycerol synthesis would be expected to be high; diacylg
lycerol acyltransferase activity was also high in brown adipose tissue
during spring and summer. In liver, however, diacylglycerol acyltrans
ferase specific activity was highest during hibernation, suggesting th
at triacylglycerol synthesis may be prominent in liver in winter. Mono
acylglycerol acyltransferase activity, which may aid in the retention
of essential fatty-acids, was 80-fold higher in liver than in white or
brown adipose tissue, but did not vary seasonally. Its dependence on
palmitoyl-CoA suggests that a divalent cation might play a role in enz
yme activation. The high hepatic diacylglycerol acyltransferase activi
ty during hibernation suggests that the metabolism of very low density
lipoprotein may be important in the movement of adipose fatty acids t
o brown adipose tissue and muscle during the rewarming that occurs per
iodically during hibernation. These studies suggest that enzymes of li
pid metabolism vary seasonally in the marmot, consistent with requirem
ents of this hibernator for triacylglycerol synthesis and metabolism.