Activation of liver carnitine palmitoyltransferase-1 and mitochondrial acetoacetyl-CoA thiolase is associated with elevated ketone body levels in the elasmobranch Squalus acanthias.
Elasmobranch fishes are an ancient group of vertebrates that have unusual lipid metabolism whereby storage lipids are mobilized from the liver for peripheral oxidation largely as ketone bodies rather than as nonesterified fatty acids under normal conditions. This reliance on ketones, even when feeding, implies that elasmobranchs are chronically ketogenic. Compared to specimens sampled within 2 d of capture (recently captured), spiny dogfish Squalus acanthias that were held for 16-33 d without apparent feeding displayed a 4.5-fold increase in plasma concentration of d- beta -hydroxybutyrate (from 0.71 to 3.2 mM) and were considered ketotic. Overt activity of carnitine palmitoyltransferase-1 in liver mitochondria from ketotic dogfish was characterized by an increased apparent maximal activity, a trend of increasing affinity (reduced apparent K(m); P=0.09) for l-carnitine, and desensitization to the inhibitor malonyl-CoA relative to recently captured animals. Acetoacetyl-CoA thiolase (ACoAT) activity in isolated liver mitochondria was also markedly increased in the ketotic dogfish compared to recently captured fish, whereas no difference in 3-hydroxy-3-methylglutaryl-CoA synthase activity was found between these groups, suggesting that ACoAT plays a more important role in the activation of ketogenesis in spiny dogfish than in mammals and birds.
Treberg
Jason R
JR
Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, Newfoundland A1C 5S7, Canada. jtreberg@mun.ca
Crockett
Elizabeth L
EL
Driedzic
William R
WR
D020155:3-Hydroxybutyric Acid / Q000378:metabolism; D000101:Acetyl-CoA C-Acetyltransferase / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism*; D004789:Enzyme Activation; D006884:Hydroxybutyrate Dehydrogenase / Q000378:metabolism; D007657:Ketone Bodies / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008928:Mitochondria / Q000201:enzymology*; D009206:Myocardium / Q000378:metabolism; D048251:Squalus acanthias / Q000378:metabolism*
D007657:Ketone Bodies; D006884:Hydroxybutyrate Dehydrogenase; D002334:Carnitine O-Palmitoyltransferase; D000101:Acetyl-CoA C-Acetyltransferase; D020155:3-Hydroxybutyric Acid