Researchers have discovered that mitochondrial trifunctional protein (TFP) enzyme activity is not altered by lysine acetylation or lysine succinylation, according to a study in PLOS One. 

Fatty acid oxidation (FAO) represents one of the body’s most important bioenergetic pathways, supplying organs such as the heart and the liver. When patients suffer from inborn errors of mitochondrial FAO, the severity of symptoms can be seen in conditions such as long chain fatty acid oxidation disorder (LCFAOD).

“Despite the prevalence of newborn screening to identify patients with these disorders, there is no effective therapy beyond dietary management. Quality of life issues and mortality remain a concern,” the researchers wrote.

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Therefore, understanding the pathways that lead to FAO disorders is of paramount importance. Dysfunctional FAO can be observed in diseases such as cancer, obesity, and diabetes. Currently, scientific literature contains insufficient (and sometimes conflicting) information on lysine acetylation and lysine succinylation in the mitochondria.

“We hypothesized that many of these conflicting results could be due to the use of acetoacetyl-CoA as a substrate when measuring TFP activity,” the researchers said.

Read more about LCFAOD etiology

They hence decided to resolve this issue, this time by using short/medium-chain hydroxy-acyl-CoA dehydrogenase (SCHAD) enzyme rather than TFP that is used in previous studies. 

The researchers used experimental mice models in their study. They found out that the assaying of TFP in SIRT3 and SIRT5 knockout mouse liver and heart mitochondria with (2E)-hexadecenoyl-CoA demonstrated no change in the activity of the enzyme.

The researchers also investigated the reactions of lysine acylation on TFP membrane binding in vitro. They found out that acylation did not alter recombinant TFP binding to cardiolipin-containing liposomes. However, they discovered that the existence of liposomes strongly abrogated the acylation reaction between succinyl-CoA and TFP lysine residues. This means that TFP may be in the membrane-bound state.


Zhang Y, Goetzman E. The enzyme activity of mitochondrial trifunctional protein is not altered by lysine acetylation or lysine succinylation. PLoS One. Published online October 13, 2021. doi:10.1371/journal.pone.0256619