Metabolic Adaptations During Lactogenesis
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1. Mammary-tissue biopsies were obtained from multiparous cows at 30 and 7 days pre partum and 7 and 40 days postpartum. Investigations of the effect of lactogenesis on fatty acid and lactose synthesis involved measurements of biosynthetic capacity (tissue-slice incubations in vitro) and activities ofrelevant enzymes. 2. Fatty acid synthesis from acetate increased over 20-fold from 30 days pre partum to 40 days post partum. Changes in the lipogenic capacity of mammary-tissue slices more closely paralleled increases in the activities of acetyl-CoA carboxylase (EC 188.8.131.52) and acetyl-CoA synthetase (EC 184.108.40.206) than of other enzymes involved in acetate incorporation into fatty acids or in NADPH generation. 3. Lactose biosynthesis by mammary-tissue slices, lactose synthetase activity (EC 220.127.116.11) and α-lactalbumin concentration were all negligible at 30 days pre partum but increased 2.5-4-fold between 7 days pre partum and 40 days post partum. Phosphoglucomutase (EC 18.104.22.168), UDP-glucose pyrophosphorylase (EC 22.214.171.124) and UDPglucose 4-epimerase (EC 126.96.36.199) had substantial activities at 30 days pre partum and increased less dramatically during lactogenesis. 4. Results are consistent with acetyl-CoA carboxylase and perhaps acetyl-CoA synthetase representing the regulatory enzyme(s) in fatty acid synthesis, with lactose synthetase (α-lactalbumin) serving a similar function in lactose biosynthesis.
KeywordsLactose Fatty Acid Synthesis Post Partum Phosphoglucomutase Acetate Incorporation
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