Enzymatic regulation of seasonal glycogen cycling in the freeze-tolerant wood frog, <em class="a-plus-plus">Rana sylvaticaem>

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• 作者：M. Clara F. do Amaral ; Richard E. Lee Jr.…
• 关键词：Rana sylvatica ; Glycogen ; Glycogen phosphorylase ; Glycogen synthase ; Protein kinase A
• 刊名：Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：186
• 期：8
• 页码：1045-1058
• 全文大小：986 KB
• 刊物类别：Biomedical and Life Sciences
• 刊物主题：Life Sciences
  Biochemistry
  Biomedicine
  Human Physiology
  Zoology
  Animal Physiology
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1432-136X
• 卷排序：186

文摘

Liver glycogen is an important energy store in vertebrates, and in the freeze-tolerant wood frog, Rana sylvatica, this carbohydrate also serves as a major source of the cryoprotectant glucose. We investigated how variation in the levels of the catalytic subunit of protein kinase A (PKAc), glycogen phosphorylase (GP), and glycogen synthase (GS) relates to seasonal glycogen cycling in a temperate (Ohioan) and subarctic (Alaskan) populations of this species. In spring, Ohioan frogs had reduced potential for glycogen synthesis, as evidenced by low GS activity and high PKAc protein levels. In addition, glycogen levels in spring were the lowest of four seasonal samples, as energy input was likely directed towards metabolism and somatic growth during this period. Near-maximal glycogen levels were reached by mid-summer, and remained unchanged in fall and winter, suggesting that glycogenesis was curtailed during this period. Ohioan frogs had a high potential for glycogenolysis and glycogenesis in winter, as evidenced by large glycogen reserves, high levels of GP and GS proteins, and high GS activity, which likely allows for rapid mobilization of cryoprotectant during freezing and replenishing of glycogen reserves during thawing. Alaskan frogs also achieved a near-maximal liver glycogen concentration by summer and displayed high glycogenic and glycogenolytic potential in winter, but, unlike Ohioan frogs, started replenishing their energy reserves early in spring. We conclude that variation in levels of both glycogenolytic and glycogenic enzymes likely happens in response to seasonal changes in energetic strategies and demands, with winter survival being a key component to understanding the regulation of glycogen cycling in this species.