Kinetic isotope effect study of N-6 methyladenosine chemical demethylation in bicarbonate-activated peroxide system.

N-6 methyladenosine is the most abundant nucleic acid modification in eukaryotes and plays a crucial role in gene regulation. The AlkB family of alpha-ketoglutarate-dependent dioxygenases is responsible for nucleic acid demethylation. Recent studies have discovered that a chemical demethylation system using hydrogen peroxide and ammonium bicarbonate can effectively demethylate nucleic acids. The addition of ferrous ammonium sulfate boosts the oxidation rate by forming a Fenton reagent with hydrogen peroxide. However, the specific mechanism and key steps of this process remain unclear. In this study, we investigate the influence of ferrous ammonium sulfate concentration on the kinetic isotope effect (KIE) of the chemical demethylation system using LC-MS. As the concentration of ferrous ions increases, the observed KIE decreases from 1.377 ± 0.020 to 1.120 ± 0.016, indicating a combination of the primary isotope effect and inverse α-secondary isotope effect with the ion pairing effect. We propose that the initial hydrogen extraction is the rate-limiting step and observe a tight transition state structure in the formation of the hm6A process through the analysis of KIE trends. The concentration-dependent KIE provides a novel perspective on the mechanism of chemical demethylation and offers a chemical model for enzyme-catalyzed demethylation.

Left Ventricular Papillary Muscle: Anatomy, Pathophysiology, and Multimodal Evaluation.

As an integral part of the mitral valve apparatus, the left ventricle papillary muscle (PM) controls mitral valve closure during systole and participates in the ejection process during left ventricular systole. Mitral regurgitation (MR) is the most immediate and predominant result when the PM is structurally or functionally abnormal. However, dysfunction of the PM is easily underestimated or overlooked in clinical interventions for MR-related diseases. Therefore, adequate recognition of PM dysfunction and PM-derived MR is critical. In this review, we systematically describe the normal anatomical variations in the PM and the pathophysiology of PM dysfunction-related diseases and summarize the commonly used parameters and the advantages and disadvantages of various noninvasive imaging modalities for the structural and functional assessment of the PM.