Hyperpolarized NMR study of the impact of pyruvate dehydrogenase kinase inhibition on the pyruvate dehydrogenase and TCA flux in type 2 diabetic rat muscle.

The role of pyruvate dehydrogenase in mediating lipid-induced insulin resistance stands as a central question in the pathogenesis of type 2 diabetes mellitus. Many researchers have invoked the Randle hypothesis to explain the reduced glucose disposal in skeletal muscle by envisioning an elevated acetyl CoA pool arising from increased oxidation of fatty acids. Over the years, in vivo NMR studies have challenged that monolithic view. The advent of the dissolution dynamic nuclear polarization NMR technique and a unique type 2 diabetic rat model provides an opportunity to clarify. Dynamic nuclear polarization enhances dramatically the NMR signal sensitivity and allows the measurement of metabolic kinetics in vivo. Diabetic muscle has much lower pyruvate dehydrogenase activity than control muscle, as evidenced in the conversion of [1-13C]lactate and [2-13C]pyruvate to HCO3- and acetyl carnitine. The pyruvate dehydrogenase kinase inhibitor, dichloroacetate, restores rapidly the diabetic pyruvate dehydrogenase activity to control level. However, diabetic muscle has a much larger dynamic change in pyruvate dehydrogenase flux than control. The dichloroacetate-induced surge in pyruvate dehydrogenase activity produces a differential amount of acetyl carnitine but does not affect the tricarboxylic acid flux. Further studies can now proceed with the dynamic nuclear polarization approach and a unique rat model to interrogate closely the biochemical mechanism interfacing oxidative metabolism with insulin resistance and metabolic inflexibility.

Hyperpolarized 13C MR Spectroscopy Depicts in Vivo Effect of Exercise on Pyruvate Metabolism in Human Skeletal Muscle.

Background Pyruvate dehydrogenase (PDH) and lactate dehydrogenase are essential for adenosine triphosphate production in skeletal muscle. At the onset of exercise, oxidation of glucose and glycogen is quickly enabled by dephosphorylation of PDH. However, direct measurement of PDH flux in exercising human muscle is daunting, and the net effect of covalent modification and other control mechanisms on PDH flux has not been assessed. Purpose To demonstrate the feasibility of assessing PDH activation and changes in pyruvate metabolism in human skeletal muscle after the onset of exercise using carbon 13 (13C) MRI with hyperpolarized (HP) [1-13C]-pyruvate. Materials and Methods For this prospective study, sedentary adults in good general health (mean age, 42 years ± 18 [standard deviation]; six men) were recruited from August 2019 to September 2020. Subgroups of the participants were injected with HP [1-13C]-pyruvate at resting, during plantar flexion exercise, or 5 minutes after exercise during recovery. In parallel, hydrogen 1 arterial spin labeling MRI was performed to estimate muscle tissue perfusion. An unpaired t test was used for comparing 13C data among the states. Results At rest, HP [1-13C]-lactate and [1-13C]-alanine were detected in calf muscle, but [13C]-bicarbonate was negligible. During moderate flexion-extension exercise, total HP 13C signals (tC) increased 2.8-fold because of increased muscle perfusion (P = .005), and HP [1-13C]-lactate-to-tC ratio increased 1.7-fold (P = .04). HP [13C]-bicarbonate-to-tC ratio increased 8.4-fold (P = .002) and returned to the resting level 5 minutes after exercise, whereas the lactate-to-tC ratio continued to increase to 2.3-fold as compared with resting (P = .008). Conclusion Lactate and bicarbonate production from hyperpolarized (HP) [1-carbon 13 {13C}]-pyruvate in skeletal muscle rapidly reflected the onset and the termination of exercise. These results demonstrate the feasibility of imaging skeletal muscle metabolism using HP [1-13C]-pyruvate MRI and the sensitivity of in vivo pyruvate metabolism to exercise states. © RSNA, 2021 Online supplemental material is available for this article.

Comparative NMR and NIRS analysis of oxygen-dependent metabolism in exercising finger flexor muscles.

Muscle contraction requires the physiology to adapt rapidly to meet the surge in energy demand. To investigate the shift in metabolic control, especially between oxygen and metabolism, researchers often depend on near-infrared spectroscopy (NIRS) to measure noninvasively the tissue O2 Because NIRS detects the overlapping myoglobin (Mb) and hemoglobin (Hb) signals in muscle, interpreting the data as an index of cellular or vascular O2 requires deconvoluting the relative contribution. Currently, many in the NIRS field ascribe the signal to Hb. In contrast, 1H NMR has only detected the Mb signal in contracting muscle, and comparative NIRS and NMR experiments indicate a predominant Mb contribution. The present study has examined the question of the NIRS signal origin by measuring simultaneously the 1H NMR, 31P NMR, and NIRS signals in finger flexor muscles during the transition from rest to contraction, recovery, ischemia, and reperfusion. The experiment results confirm a predominant Mb contribution to the NIRS signal from muscle. Given the NMR and NIRS corroborated changes in the intracellular O2, the analysis shows that at the onset of muscle contraction, O2 declines immediately and reaches new steady states as contraction intensity rises. Moreover, lactate formation increases even under quite aerobic condition.

Myoglobin and the regulation of mitochondrial respiratory chain complex IV.

KEY POINTS: Mitochondrial respiration is regulated by multiple elaborate mechanisms. It has been shown that muscle specific O2 binding protein, Myoglobin (Mb), is localized in mitochondria and interacts with respiratory chain complex IV, suggesting that Mb could be a factor that regulates mitochondrial respiration. Here, we demonstrate that muscle mitochondrial respiration is improved by Mb overexpression via up-regulation of complex IV activity in cultured myoblasts; in contrast, suppression of Mb expression induces a decrease in complex IV activity and mitochondrial respiration compared with the overexpression model. The present data are the first to show the biological significance of mitochondrial Mb as a potential modulator of mitochondrial respiratory capacity. ABSTRACT: Mitochondria are important organelles for metabolism, and their respiratory capacity is a primary factor in the regulation of energy expenditure. Deficiencies of cytochrome c oxidase complex IV, which reduces O2 in mitochondria, are linked to several diseases, such as mitochondrial myopathy. Moreover, mitochondrial respiration in skeletal muscle tissue tends to be susceptible to complex IV activity. Recently, we showed that the muscle-specific protein myoglobin (Mb) interacts with complex IV. The precise roles of mitochondrial Mb remain unclear. Here, we demonstrate that Mb facilitates mitochondrial respiratory capacity in skeletal muscles. Although mitochondrial DNA copy numbers were not altered in Mb-overexpressing myotubes, O2 consumption was greater in these myotubes than that in mock cells (Mock vs. Mb-Flag::GFP: state 4, 1.00 ± 0.09 vs. 1.77 ± 0.34; state 3, 1.00 ± 0.29; Mock: 1.60 ± 0.53; complex 2-3-4: 1.00 ± 0.30 vs. 1.50 ± 0.44; complex IV: 1.00 ± 0.14 vs. 1.87 ± 0.27). This improvement in respiratory capacity could be because of the activation of enzymatic activity of respiratory complexes. Moreover, mitochondrial respiration was up-regulated in myoblasts transiently overexpressing Mb; complex IV activity was solely activated in Mb-overexpressing myoblasts, and complex IV activity was decreased in the myoblasts in which Mb expression was suppressed by Mb-siRNA transfection (Mb vector transfected vs. Mb vector, control siRNA transfected vs. Mb vector, Mb siRNA transfected: 0.15 vs. 0.15 vs. 0.06). Therefore, Mb enhances the enzymatic activity of complex IV to ameliorate mitochondrial respiratory capacity, and could play a pivotal role in skeletal muscle metabolism.

Palmitate interaction with physiological states of myoglobin.

BACKGROUND: Previous studies have shown that palmitate (PA) can bind specifically and non-specifically to Fe(III)MbCN. The present study has observed PA interaction with physiological states of Fe(II)Mb, and the observations support the hypothesis that Mb may have a potential role in facilitating intracellular fatty acid transport. METHODS: 1H NMR spectra measurements of the Mb signal during PA titration show signal changes consistent with specific and non-specific binding. RESULTS: Palmitate (PA) interacts differently with physiological states of Mb. Deoxy Mb does not interact specifically or non-specifically with PA, while the carbonmonoxy myoglobin (MbCO) interaction with PA decreases the intensity of selective signals and produces a 0.15ppmupfield shift of the PAmethylene peak. The selective signal change upon PA titration provides a basis to determine an apparent PA binding constant,which serves to create a model comparing the competitive PA binding and facilitated fatty acid transport of Mb and fatty acid binding protein(FABP). CONCLUSIONS: Given contrasting PA interaction of ligated vs. unligated Mb, the cellular fatty acid binding protein(FABP) and Mb concentration in the cell, the reported cellular diffusion coefficients, the PA dissociation constants from ligated Mb and FABP, a fatty acid flux model suggests that Mb can compete with FABP transporting cellular fatty acid. GENERAL SIGNIFICANCE: Under oxygenated conditions and continuous energy demand, Mb dependent fatty acid transport could influence the cell's preference for carbohydrate or fatty acid as a fuel source and regulate fatty acid metabolism.

Hyperpolarized 13C NMR observation of lactate kinetics in skeletal muscle.

The production of glycolytic end products, such as lactate, usually evokes a cellular shift from aerobic to anaerobic ATP generation and O2 insufficiency. In the classical view, muscle lactate must be exported to the liver for clearance. However, lactate also forms under well-oxygenated conditions, and this has led investigators to postulate lactate shuttling from non-oxidative to oxidative muscle fiber, where it can serve as a precursor. Indeed, the intracellular lactate shuttle and the glycogen shunt hypotheses expand the vision to include a dynamic mobilization and utilization of lactate during a muscle contraction cycle. Testing the tenability of these provocative ideas during a rapid contraction cycle has posed a technical challenge. The present study reports the use of hyperpolarized [1-(13)C]lactate and [2-(13)C]pyruvate in dynamic nuclear polarization (DNP) NMR experiments to measure the rapid pyruvate and lactate kinetics in rat muscle. With a 3 s temporal resolution, (13)C DNP NMR detects both [1-(13)C]lactate and [2-(13)C]pyruvate kinetics in muscle. Infusion of dichloroacetate stimulates pyruvate dehydrogenase activity and shifts the kinetics toward oxidative metabolism. Bicarbonate formation from [1-(13)C]lactate increases sharply and acetyl-l-carnitine, acetoacetate and glutamate levels also rise. Such a quick mobilization of pyruvate and lactate toward oxidative metabolism supports the postulated role of lactate in the glycogen shunt and the intracellular lactate shuttle models. The study thus introduces an innovative DNP approach to measure metabolite transients, which will help delineate the cellular and physiological role of lactate and glycolytic end products.

Data on mitochondrial respiratory function in skeletal muscle of adult male mice in response to 3-weeks heat stress.

Chronic heat stress induces mitochondrial adaptation in skeletal muscle. However, the effect of chronic heat stress on the respiratory function per mitochondria in skeletal muscle has not been well studied. Here, the present study reports on the effect of 3-weeks heat stress on muscle mitochondrial respiration using male C57BL/6JJ mice at age 21 weeks. Mice were randomly assigned to either the control group (n = 6) or passive heat group (n = 6). After 3-weeks of heat stress, the right triceps surae was removed and used for biochemical analysis. Protein expression was assessed by immunoblotting. Mitochondrial respiratory function was measured by Oxygraph-2k. The study also shows the impact of the heat stress on daily feeding, body weight, muscle weight, and protein expression of heat shock proteins (heat-response marker).

Endurance training increases mitochondrial myoglobin and enhances its interaction with complex IV in rat plantaris muscle.

AIM: Endurance exercise training is known to increase mitochondrial respiration in skeletal muscle. However, the molecular mechanisms behind this are not fully understood. Myoglobin (Mb) is a member of the globin family, which is highly expressed in skeletal and cardiac muscles. We recently found that Mb localizes inside mitochondria in skeletal muscle and interacts with cytochrome c oxidase subunit IV (COXIV), a subunit of mitochondrial complex IV, which regulates respiration by augmenting complex IV activity. In the present study, we investigated the effect of endurance training on Mb-COXIV interaction within mitochondria in rat skeletal muscle. METHODS: Eight-week-old male Wistar rats were subjected to 6-week treadmill running training. Forty-eight hours after the last training session, the plantaris muscle was removed under anesthesia and used for biochemical analysis. RESULTS: The endurance training increased mitochondrial content in the skeletal muscle. It also augmented complex IV-dependent oxygen consumption and complex IV activity in isolated mitochondria from skeletal muscle. Furthermore, endurance training increased Mb expression at the whole muscle level. Importantly, mitochondrial Mb content and Mb-COXIV binding were increased by endurance training. CONCLUSION: These findings suggest that an increase in mitochondrial Mb and the concomitant enhancement of Mb interaction with COXIV may contribute to the endurance training-induced upregulation of mitochondrial respiration by augmenting complex IV activity.

TOM complex-independent transport pathway of myoglobin into mitochondria in C2C12 myotubes.

Recently, we found that myoglobin (Mb) localizes in both the cytosol and mitochondrial intermembrane space in rodent skeletal muscle. Most proteins of the intermembrane space pass through the outer mitochondrial membrane via the translocase of the outer membrane (TOM) complex. However, whether the TOM complex imports Mb remains unknown. The purpose of this study was to investigate the involvement of the TOM complex in Mb import into the mitochondria. A proteinase K protection assay of mitochondria from C2C12 myotubes confirmed that Mb integrated into the mitochondria. An immunoprecipitation assay verified the interaction of Mb and TOM complex receptors (Tom20, Tom70) in isolated mitochondria. The assay showed a clear interaction of Mb with Tom20 and Tom70. A knockdown experiment using siRNA for TOM complex receptors (Tom20, Tom70) and TOM complex channel (Tom40) did not alter the amount of Mb expression in the mitochondrial fraction. These results suggested that Mb does not necessarily require the TOM complex for mitochondrial import of Mb. Although the physiological role of Mb interactions with TOM complex receptors remains unclear, further studies are needed to clarify how Mb enters the mitochondria independently of the TOM complex.

Imaging apolipoprotein AI in vivo.

Coronary disease risk increases inversely with high-density lipoprotein (HDL) level. The measurement of the biodistribution and clearance of HDL in vivo, however, has posed a technical challenge. This study presents an approach to the development of a lipoprotein MRI agent by linking gadolinium methanethiosulfonate (Gd[MTS-ADO3A]) to a selective cysteine mutation in position 55 of apo AI, the major protein of HDL. The contrast agent targets both liver and kidney, the sites of HDL catabolism, whereas the standard MRI contrast agent, gadolinium-diethylenetriaminepentaacetic acid-bismethylamide (GdDTPA-BMA, gadodiamide), enhances only the kidney image. Using a modified apolipoprotein AI to create an HDL contrast agent provides a new approach to investigate HDL biodistribution, metabolism and regulation in vivo.

Localization of myoglobin in mitochondria: implication in regulation of mitochondrial respiration in rat skeletal muscle.

Mitochondria play a principal role in metabolism, and mitochondrial respiration is an important process for producing adenosine triphosphate. Recently, we showed the possibility that the muscle-specific protein myoglobin (Mb) interacts with mitochondrial complex IV to augment the respiration capacity in skeletal muscles. However, the precise mechanism for the Mb-mediated upregulation remains under debate. The aim of this study was to ascertain whether Mb is truly integrated into the mitochondria of skeletal muscle and to investigate the submitochondrial localization. Isolated mitochondria from rat gastrocnemius muscle were subjected to different proteinase K (PK) concentrations to digest proteins interacting with the outer membrane. Western blotting analysis revealed that the PK digested translocase of outer mitochondrial membrane 20 (Tom20), and the immunoreactivity of Tom20 decreased with the amount of PK used. However, the immunoreactivity of Mb with PK treatment was better preserved, indicating that Mb is integrated into the mitochondria of skeletal muscle. The mitochondrial protease protection assay experiments suggested that Mb localizes within the mitochondria in the inner membrane from the intermembrane space side. These results strongly suggest that Mb inside muscle mitochondria could be implicated in the regulation of mitochondrial respiration via complex IV.

Quantification of myoglobin deoxygenation and intracellular partial pressure of O2 during muscle contraction during haemoglobin-free medium perfusion.

Although the O(2) gradient regulates O(2) flux from the capillary into the myocyte to meet the energy demands of contracting muscle, intracellular O(2) dynamics during muscle contraction remain unclear. Our hindlimb perfusion model allows the determination of intracellular myoglobin (Mb) saturation ( ) and intracellular oxygen tension of myoglobin ( ) in contracting muscle using near infrared spectroscopy (NIRS). The hindlimb of male Wistar rats was perfused from the abdominal aorta with a well-oxygenated haemoglobin-free Krebs-Henseleit buffer. The deoxygenated Mb ([deoxy-Mb]) signal was monitored by NIRS. Based on the value of [deoxy-Mb], and were calculated, and the time course was evaluated by an exponential function model. Both and started to decrease immediately after the onset of contraction. The steady-state values of and progressively decreased with relative work intensity or muscle oxygen consumption. At the maximal twitch rate, and were 49% and 2.4 mmHg, respectively. Moreover, the rate of release of O(2) from Mb at the onset of contraction increased with muscle oxygen consumption. These results suggest that at the onset of muscle contraction, Mb supplies O(2) during the steep decline in , which expands the O(2) gradient to increase the O(2) flux to meet the increased energy demands.

Myoglobin's old and new clothes: from molecular structure to function in living cells.

Myoglobin, a mobile carrier of oxygen, is without a doubt an important player central to the physiological function of heart and skeletal muscle. Recently, researchers have surmounted technical challenges to measure Mb diffusion in the living cell. Their observations have stimulated a discussion about the relative contribution made by Mb-facilitated diffusion to the total oxygen flux. The calculation of the relative contribution, however, depends upon assumptions, the cell model and cell architecture, cell bioenergetics, oxygen supply and demand. The analysis suggests that important differences can be observed whether steady-state or transient conditions are considered. This article reviews the current evidence underlying the evaluation of the biophysical parameters of myoglobin-facilitated oxygen diffusion in cells, specifically the intracellular concentration of myoglobin, the intracellular diffusion coefficient of myoglobin and the intracellular myoglobin oxygen saturation. The review considers the role of myoglobin in oxygen transport in vertebrate heart and skeletal muscle, in the diving seal during apnea as well as the role of the analogous leghemoglobin of plants. The possible role of myoglobin in intracellular fatty acid transport is addressed. Finally, the recent measurements of myoglobin diffusion inside muscle cells are discussed in terms of their implications for cytoarchitecture and microviscosity in these cells and the identification of intracellular impediments to the diffusion of proteins inside cells. The recent experimental data then help to refine our understanding of Mb function and establish a basis for future investigation.

'It's hollow': the function of pores within myoglobin.

Despite a century of research, the cellular function of myoglobin (Mb), the mechanism regulating oxygen (O(2)) transport in the cell and the structure-function relationship of Mb remain incompletely understood. In particular, the presence and function of pores within Mb have attracted much recent attention. These pores can bind to Xe as well as to other ligands. Indeed, recent cryogenic X-ray crystallographic studies using novel techniques have captured snapshots of carbon monoxide (CO) migrating through these pores. The observed movement of the CO molecule from the heme iron site to the internal cavities and the associated structural changes of the amino acid residues around the cavities confirm the integral role of the pores in forming a ligand migration pathway from the protein surface to the heme. These observations resolve a long-standing controversy - but how these pores affect the physiological function of Mb poses a striking question at the frontier of biology.

NIRS measurement of O(2) dynamics in contracting blood and buffer perfused hindlimb muscle.

In order to obtain evidence that Mb releases O(2) during muscle contraction, we have set up a buffer-perfused hindlimb rat model and applied NIRS to detect the dynamics of tissue deoxygenation during contraction. The NIRS signal was monitored on hindlimb muscle during twitch contractions at 1 Hz, evoked via electrostimulator at different submaximal levels. The hindlimb perfusion was carried out by perfusion of Krebs Bicarbonate buffer. The NIRS still detected a strong signal even under Hb-free contractions. The deoxygenation signal (Delta[deoxy]) was progressively increased at onset of the contraction and reached the plateau under both blood- and buffer-perfused conditions. However, the amplitude of Delta[deoxy] during steady state continued to significantly increase as tension increased. The tension-matched comparison of the Delta[deoxy] level under buffer-perfused and blood perfused conditions indicate that Mb can contribute approximately 50% to the NIRS signal. These results clarify the Mb contribution to the NIRS signal and show a falling intracellular PO(2) as workload increases.

A mouse model and 19 F NMR approach to investigate the effects of sialic acid supplementation on cognitive development.

Researchers have observed that a sialic acid (Sia)-supplemented neonatal diet leads to improved cognition in weanling piglets. However, whether cognitive improvement appears with different physiological backgrounds and persists into adulthood is not known. Here, we have established a convenient mouse model and used an 19 F NMR approach to address these questions, test the conditionally essential nutrient hypothesis about Sia supplementation, and assess the prospect of measuring Sia metabolism directly in vivo. Indeed, the neonatal mouse brain uptakes more Sia than the adult brain, and Sia supplementation of neonatal mice improves the cognitive performance of adult mice. The non-invasive 19 F NMR approach and viable mouse model opens unique opportunities for clarifying the interplay of nutritional supplementation, metabolism, and cognitive development.

Impaired skeletal muscle mitochondrial bioenergetics and physical performance in chronic kidney disease.

The maintenance of functional independence is the top priority of patients with chronic kidney disease (CKD). Defects in mitochondrial energetics may compromise physical performance and independence. We investigated associations of the presence and severity of kidney disease with in vivo muscle energetics and the association of muscle energetics with physical performance. We performed measures of in vivo leg and hand muscle mitochondrial capacity (ATPmax) and resting ATP turnover (ATPflux) using 31phosphorus magnetic resonance spectroscopy and oxygen uptake (O2 uptake) by optical spectroscopy in 77 people (53 participants with CKD and 24 controls). We measured physical performance using the 6-minute walk test. Participants with CKD had a median estimated glomerular filtration rate (eGFR) of 33 ml/min per 1.73 m2. Participants with CKD had a -0.19 mM/s lower leg ATPmax compared with controls but no difference in hand ATPmax. Resting O2 uptake was higher in CKD compared with controls, despite no difference in ATPflux. ATPmax correlated with eGFR and serum bicarbonate among participants with GFR <60. ATPmax of the hand and leg correlated with 6-minute walking distance. The presence and severity of CKD associate with muscle mitochondrial capacity. Dysfunction of muscle mitochondrial energetics may contribute to reduced physical performance in CKD.

Oximetry with the NMR signals of hemoglobin Val E11 and Tyr C7.

The NMR visibility of the signals from erythrocyte hemoglobin (Hb) presents an opportunity to assess the vascular PO(2) (partial pressure of oxygen) in vivo to gather insight into the regulation of O(2) transport, especially in contracting muscle tissue. Some concerns, however, have arisen about the validity of using the Val E11 signal as an indicator of PO(2), since its intensity depends on tertiary structural changes, in contrast to the quaternary structure changes associated with relaxed (R) and tense (T) transition during O(2) binding. We have examined the Val E11 and Tyr C7 signal intensity as a function of Hb saturation by developing an oximetry system, which permits the comparative analysis of the NMR and spectrophotometric measurements. The spectrophotometric assay defines the Hb saturation level at a given PO(2) and yields standard oxygen-binding curves. Under defined PO(2) and Hb saturation values, the NMR measurements have determined that the Val E11 signal, as well as the Tyr C7 signal, tracks closely Hb saturation and can therefore serve as a vascular oxygen biomarker.

Interaction of fatty acid with myoglobin.

Upon titration with palmitate, the (1)H NMR spectra of metmyoglobin cyanide (MbCN) reveal a selective perturbation of the 8 heme methyl, consistent with a specific interaction of myoglobin (Mb) with fatty acid. Other detectable hyperfine shifted resonances of the heme group remain unchanged. Mb also enhances fatty acid solubility, as reflected in a more intense methylene peak of palmitate in Mb solution than in Tris buffer. Ligand binding analysis indicates an apparent palmitate dissociation constant (K(d)) of 43microM. These results suggest that Mb can bind fatty acid and may have a role in facilitating fatty acid transport in the cell.

Differential Interaction of Myoglobin with Select Fatty Acids of Carbon Chain Lengths C8 to C16.

Previous studies have shown that palmitic acid (PAM) and oleic acid (OLE) can bind myoglobin (Mb). How fatty acids (FA) with different carbon chain lengths and sulfate substitution interact with Mb remains uncertain. Indeed, C8:0 and C10:0 fatty acids do not perturb the intensities of the 1H-NMR MbCN signal intensity at FA:Mb ratios below 2:1. Starting with C12:0, C12:0-C16:0, FA induce a noticeable spectral change. C12:0 and C14:0 FA affect both the 5- and 8-heme methyl signals, whereas the C16:0 FA perturbs only the 8-heme methyl signal. All C12:0-C16:0 saturated FA induce upfield shifts in the -CH2 peak of different FA in the presence of Mb. Increasing the apparent solubility with a sulfate group substitution enhances the FA interaction of lauric sulfate (LAU 1-SO4) but not palmitate sulfate acid (PAM 1-SO4). The detergent (DET) property of FA has no significant contribution. Common positive, neutral, and negative DET at DET:Mb ratio of 1:1 induce no perturbation of the MbCN spectra. The experiment observations establish a basis to investigate the molecular mechanism underlying the FA interaction with Mb.