Raymond James A
School of Life Sciences, University of Nevada Las Vegas, Las Vegas, NV, 89154, USA,
Fish Physiol Biochem. 2015 Jun;41(3):811-8. doi: 10.1007/s10695-015-0048-7. Epub 2015 Apr 2.
Winter-acclimated rainbow smelt (Osmerus mordax Mitchill) produce high levels of glycerol as an antifreeze. A common pathway to glycerol involves the enzyme glycerol-3-phosphate phosphatase (GPP), but no GPP has yet been identified in fish or any other animal. Here, two phosphatases assembled from existing EST libraries (from winter-acclimated smelt and cold-acclimated smelt hepatocytes) were found to resemble a glycerol-associated phosphatase from a glycerol-producing alga, Dunaliella salina, and a recently discovered GPP from a bacterium, Mycobacterium tuberculosis. Recombinant proteins were generated and were found to have GPP activity on the order of a few μMol Pi/mg enzyme/min. The two enzymes have acidic pH optima (~5.5) similar to that previously determined for GPP activity in liver tissue, with about 1/3 of their peak activities at neutral pH. The two enzymes appear to account for the GPP activity of smelt liver, but due to their reduced activities at neutral pH, their contributions to glycerol production in vivo remain unclear. Similar enzymes may be active in a glycerol-producing insect, Dendroctonus ponderosae.
经过冬季驯化的彩虹香鱼（Osmerus mordax Mitchill）会产生大量甘油作为抗冻剂。甘油的常见合成途径涉及甘油-3-磷酸磷酸酶（GPP），但在鱼类或任何其他动物中尚未鉴定出GPP。在此，从现有的EST文库（来自经过冬季驯化的香鱼和经过冷驯化的香鱼肝细胞）中组装的两种磷酸酶被发现类似于来自产甘油藻类杜氏盐藻（Dunaliella salina）的一种与甘油相关的磷酸酶，以及最近从细菌结核分枝杆菌（Mycobacterium tuberculosis）中发现的GPP。生成了重组蛋白，并发现其GPP活性约为几微摩尔无机磷/毫克酶/分钟。这两种酶的最适酸性pH值（约5.5）与先前在肝组织中测定的GPP活性相似，在中性pH值下其峰值活性约为三分之一。这两种酶似乎解释了香鱼肝中的GPP活性，但由于它们在中性pH值下活性降低，其对体内甘油生成的贡献仍不清楚。类似的酶可能在产甘油昆虫西松大小蠹（Dendroctonus ponderosae）中具有活性。
