This study determined that the malate-aspartate shuttle is a key regulator of embryo metabolism and therefore viability and is the first report that mouse zygotes can develop normally to term in the absence of pyruvate.ġ The abbreviations used are: MAS, malate-aspartate shuttle AspAT, aspartate aminotransferase mAspAT, mitochondrial AspAT cAspAT, cytoplasmic AspAT mMDH, mitochondrial malate dehydrogenase cMDH, cytoplasmic malate dehydrogenase MOPS, 4-morpholinepropanesulfonic acid AOA, amino-oxyacetate LDH, lactate dehydrogenase. Addition of high concentrations of exogenous aspartate to the culture medium enabled mouse zygotes to utilize lactate in the absence of pyruvate and develop normally to the blastocyst stage as well as produce normal viable offspring. It was determined that aspartate was a rate-limiting factor in the activity of the malate-aspartate shuttle in mouse zygotes probably due to the high Km of the cytoplasmic aspartate aminotransferase. The mRNA for the four enzymes for shuttle activity were detected at all stages of development. Furthermore, the inability of the mouse zygote to use lactate as an energy source was a result of a lack of malate-aspartate shuttle activity. Activity of the malate-aspartate shuttle was found to be essential for the metabolism of lactate in the two-cell embryo. This study has determined for the first time that mitochondrial reducing equivalent shuttles regulate metabolism in the early embryo. Pyruvate has been considered the sole substrate that can support development of the mouse zygote to the two-cell stage, with lactate able to support development from the two-cell stage. Glycobiology and Extracellular Matrices.Total ATP produced is the sum of all ATP produced in different steps of any cycle or pathway. Net gain of ATP means: produced ATP - consumed ATP.

Note: There is a difference between the net gain of ATP and the number of ATP molecules produced. The number of ATP molecules formed via the malate-aspartate shuttle is 38 ATP. This enzyme catalyzes the reaction of oxaloacetate and NADH to produce malate and $ $ which is present in the cytosol can further be reduced again by another cycle of glycolysis, and the NADH in the matrix can be further used for ATP synthesis. So this process starts in the cytosol by malate dehydrogenase. The important enzyme in the malate-aspartate shuttle is malate dehydrogenase. Hint: The malate-aspartate shuttle is a process in which electrons produced during glycolysis are transferred across the semipermeable membrane of the mitochondria, specifically the inner membrane for oxidative phosphorylation.

Malate aspartate shuttle