Thermal thresholds of lipid restructuring and delta(9)-desaturase expression in the liver of carp (Cyprinus carpio L.).
Cold acclimation induces a transient enzymatic activation of the acyl CoA-(&Dgr;)(9)-desaturase in carp liver. We have determined thresholds for two underlying mechanisms; namely, the activation of latent enzyme and the induced synthesis of new desaturase. Carp were progressively cooled from 30 degrees C to 23, 17 and 10 degrees C, where they were held for up to 5 days. Endoplasmic reticulum phospholipids showed substantial changes in fatty acid composition, with linear decreases in the proportion of saturates with temperature over the full range of cooling (11.3 % in phosphatidylcholine and 15.8 % in phosphatidylethanolamine). In the phosphatidyl-ethanolamine fraction, this was linked to increased proportions of monoenes, particularly 20:1(n-9). Modest cooling to 23 degrees C on day 1 induced a 2.5-fold transient increase in delta(9)-desaturase activity without any change in the amount of desaturase protein or transcript. Further cooling to 17 degrees C induced a greater and more sustained increase in desaturase activity, reaching sevenfold on day 5, with a 10- to 20-fold increase in the amount of desaturase transcript. Extreme cooling to 10 degrees C led to a very large, but transient, 40- to 50-fold increase in desaturase transcript amounts, a modest 40-50 % increase in desaturase protein but no further increase in activity over that observed at 17 degrees C. These results distinguish at least three mechanisms involved in cold-induced lipid restructuring; the activation of latent desaturase observed with gentle cooling, the induction of desaturase gene transcription and, finally, a third unidentified lipid compensatory mechanism that occurs with extreme cooling. The complex nature of cold-induced lipid restructuring also involves changes in the activity of other biosynthetic enzymes, including elongase and positional- and phospholipid-specific acyltransferases.
Trueman
R J
RJ
Integrative Physiology Research Group, School of Biological Sciences, University of Liverpool, Liverpool L69 3BX, UK.
Tiku
P E
PE
Caddick
M X
MX
Cossins
A R
AR
D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D016880:Anisotropy; D002347:Carps / Q000502:physiology*; D003080:Cold Temperature; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008099:Liver / Q000737:chemistry / Q000378:metabolism*; D008862:Microsomes, Liver / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013230:Stearoyl-CoA Desaturase / Q000096:biosynthesis / Q000378:metabolism*
D005227:Fatty Acids; D008055:Lipids; D012333:RNA, Messenger; D013230:Stearoyl-CoA Desaturase