The sirtuins are a class of enzymes that regulate various metabolic processes by removing post-translational modifications from enzymes. SIRT4 is an autosomally encoded sirtuin protein that colocalizes with the pyruvate dehydrogenase complex. It deacylates lysine (Lys) residues on certain metabolic proteins by removing methylglutaryl and hydroxymethylglutaryl units. Methylglutaryl-CoA and hydroxymethylglutaryl-CoA are intermediates in leucine (Leu) catabolism, and scientists hypothesized that SIRT4 regulates this pathway. To test their hypothesis, livers from wild-type (WT) and SIRT4 knockout (KO) mice were treated with α-keto acid derivatives of several amino acids, including the derivative produced from leucine transamination, α-ketoisocaproate (αKIC). Figures 1 and 2 show the rate of oxidation of α-keto acids and oxygen consumption in both WT and KO livers, respectively.Figure 1 Box plot showing the rate of oxidation of α-ketoisocaproate (αKIC), α-ketoglutarate (αKG), and pyruvate in SIRT4 knockout livers (Note: Asterisk indicates p < 0.05 relative to WT level.)Figure 2 Oxygen consumption in WT and KO livers in the presence and absence of succinate and reduced cytochrome C (Cyt-C) (Note: Error bars represent the standard error of the mean (SEM).)Because leucine is known to regulate insulin secretion, scientists injected WT and KO mice with leucine and measured plasma insulin levels over time. They then injected mice with insulin and monitored blood glucose levels (Figure 3).Figure 3 (A) Plasma insulin levels after injection with leucine and (B) blood glucose levels after injection with insulin in both WT and KO miceAdapted from Anderson KA, Huynh FK, Fisher-Wellman K, et al. SIRT4 Is a Lysine Deacylase That Controls Leucine Metabolism and Insulin Secretion. Cell Metab. 2017;25(4):838-855.e15. Question 29In the absence of SIRT4, the electrochemical potential across the inner mitochondrial membrane:A.is increased relative to mitochondria in the presence of SIRT4.B.is decreased relative to mitochondria in the presence of SIRT4.C.is not changed relative to mitochondria in the presence of SIRT4.D.is increased relative to mitochondria with SIRT4 only when cytochrome C is added.
Question
The sirtuins are a class of enzymes that regulate various metabolic processes by removing post-translational modifications from enzymes. SIRT4 is an autosomally encoded sirtuin protein that colocalizes with the pyruvate dehydrogenase complex. It deacylates lysine (Lys) residues on certain metabolic proteins by removing methylglutaryl and hydroxymethylglutaryl units. Methylglutaryl-CoA and hydroxymethylglutaryl-CoA are intermediates in leucine (Leu) catabolism, and scientists hypothesized that SIRT4 regulates this pathway. To test their hypothesis, livers from wild-type (WT) and SIRT4 knockout (KO) mice were treated with α-keto acid derivatives of several amino acids, including the derivative produced from leucine transamination, α-ketoisocaproate (αKIC). Figures 1 and 2 show the rate of oxidation of α-keto acids and oxygen consumption in both WT and KO livers, respectively.Figure 1 Box plot showing the rate of oxidation of α-ketoisocaproate (αKIC), α-ketoglutarate (αKG), and pyruvate in SIRT4 knockout livers (Note: Asterisk indicates p < 0.05 relative to WT level.)Figure 2 Oxygen consumption in WT and KO livers in the presence and absence of succinate and reduced cytochrome C (Cyt-C) (Note: Error bars represent the standard error of the mean (SEM).)Because leucine is known to regulate insulin secretion, scientists injected WT and KO mice with leucine and measured plasma insulin levels over time. They then injected mice with insulin and monitored blood glucose levels (Figure 3).Figure 3 (A) Plasma insulin levels after injection with leucine and (B) blood glucose levels after injection with insulin in both WT and KO miceAdapted from Anderson KA, Huynh FK, Fisher-Wellman K, et al. SIRT4 Is a Lysine Deacylase That Controls Leucine Metabolism and Insulin Secretion. Cell Metab. 2017;25(4):838-855.e15. Question 29In the absence of SIRT4, the electrochemical potential across the inner mitochondrial membrane:A.is increased relative to mitochondria in the presence of SIRT4.B.is decreased relative to mitochondria in the presence of SIRT4.C.is not changed relative to mitochondria in the presence of SIRT4.D.is increased relative to mitochondria with SIRT4 only when cytochrome C is added.
Solution
To answer this question, we need to understand the role of SIRT4 and its impact on the mitochondrial membrane potential.
SIRT4 is a mitochondrial enzyme that regulates various metabolic processes. In the context of this question, it's important to note that SIRT4 is involved in the regulation of the leucine metabolism pathway.
The question is asking about the electrochemical potential across the inner mitochondrial membrane in the absence of SIRT4. The electrochemical potential across the inner mitochondrial membrane is primarily established by the electron transport chain, which generates a proton gradient that drives ATP synthesis.
The study shows that in the absence of SIRT4 (in SIRT4 knockout mice), there is an increased rate of oxidation of α-ketoisocaproate (αKIC), a derivative of leucine. This suggests that without SIRT4, there is an increase in the metabolic activity related to leucine.
Increased metabolic activity could lead to an increased rate of electron transport and thus an increased proton gradient across the inner mitochondrial membrane. This would suggest that the electrochemical potential across the inner mitochondrial membrane is increased in the absence of SIRT4.
Therefore, the answer to the question would be:
A. is increased relative to mitochondria in the presence of SIRT4.
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