SUIT-011

high-resolution terminology - matching measurements at high-resolution

SUIT-011

Description

Abbreviation: GM+S_OXPHOS+Rot_ET

Reference: A: Maximum mitochondrial respiratory capacity (OXPHOS with NS substrates) and coupling/pathway control

SUIT protocol pattern: 1GM;2D;2c;3S;4U;5Rot-

The SUIT-011 protocols are designed to study physiologically relevant maximum mitochondrial respiratory capacity (OXPHOS with NS substrates) and coupling/pathway control states. SUIT-011 gives information of the linear coupling control (L- P) with NADH linked-substrates (GM). GM and PM yield practically identical fluxes in human skeletal muscle fibres. However, PM is the superior alternative to GM, since the fractions of the N-pathway is lower and of the S-pathway is higher with GM compared to PM. PM, therefore, yields a more sensitive assay for the diagnosis of injuries in the N-linked pathway (compare SUIT-001 and SUIT-004). Moreover, SUIT-011 allows the evaluation of the coupling-control state (P- E) with NADH and succinate linked-substrates (NS) and the pathway control in OXPHOS (NS) and ET state (NS and S). SUIT-011 can be extended with the CIV assay module.

Communicated by Doerrier C and Gnaiger E (last update 2019-06-05)

Specific SUIT protocols

• SUIT-011 O2 pfi D024 for permeabilized fibers

Steps and respiratory states

Step	State	Pathway	Q-junction	Comment - Events (E) and Marks (M)
1GM	GML(n)	N	CI	1GM NADH-linked substrates (type N-pathway to Q). Non-phosphorylating resting state (LEAK state); LEAK respiration L(n) in the absence of ADP, ATP, AMP (no adenylates).
2D	GMP	N	CI	1GM;2D NADH-linked substrates (type N-pathway to Q). OXPHOS capacity P (with saturating [ADP]), active OXPHOS state.
2c	GMcP	N	CI	1GM;2D;2c NADH-linked substrates (type N-pathway to Q). OXPHOS capacity P (with saturating [ADP]), active OXPHOS state. Addition of cytochrome c yields a test for integrity of the mtOM (cytochrome c control efficiency). Stimulation by added cytochrome c would indicate an injury of the mtOM and limitation of respiration in the preceding state without added c due to loss of cytochrome c. Typically, cytochrome c is added immediately after the earliest ADP-activation step (OXPHOS capacity P with saturating [ADP]).
3S	GMSP	NS	CI&II	1GM;2D;2c;3S NADH-linked substrates (type N-pathway to Q). & Succinate, S ( type S-pathway to Q). Respiratory stimulation by simultaneous action of type N substrates & succinate, with convergent electron flow in the NS-pathway for reconstitution of TCA cycle function. OXPHOS capacity P (with saturating [ADP]), active OXPHOS state.
4U	GMSE	NS	CI&II	1GM;2D;2c;3S;4U Respiratory stimulation by simultaneous action of type N substrates & succinate, with convergent electron flow in the NS-pathway for reconstitution of TCA cycle function. Uncoupler titration (avoiding inhibition by high uncoupler concentrations) to obtain electron transfer (ET) capacity E (noncoupled ET-state). Test for limitation of OXPHOS capacity P by the phosphorylation system (ANT, ATP synthase, phosphate transporter) relative to ET capacity E in mt-preparations: E-P control efficiency and E-L coupling efficiency. In living cells: E-R control efficiency and E-L coupling efficiency.
5Rot	SE	S	CII	1GM;2D;2c;3S;4U;5Rot Succinate pathway control state (S-pathway) after inhibiting CI with rotenone, which also inhibits the F-pathway. Noncoupled electron transfer state, ET state, with ET capacity E.
6Ama	ROX			1GM;2D;2c;3S;4U;5Rot;6Ama Rox is the residual oxygen consumption in the ROX state, due to oxidative side reactions, estimated after addition of antimycin A (inhibitor of CIII). Rox is subtracted from oxygen flux as a baseline for all respiratory states, to obtain mitochondrial respiration (mt).

Step	Respiratory state	Pathway control	ET-Complex	Comment
## AsTm	AsTmE	CIV	CIV
## Azd	CHB

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Coupling control

» Coupling control state

» ET capacity

» OXPHOS capacity

» LEAK respiration

Pathway control

» Electron transfer pathway

» Fatty acid oxidation pathway control state, F

» NADH electron transfer-pathway state, N

» Succinate pathway control state, S

» NS-pathway control state, NS

» Glycerophosphate pathway control state, Gp

» Complex IV single step, CIV

» Anaplerotic pathway control state

Main fuel substrates

» Glutamate, G

» Glycerophosphate, Gp

» Malate, M

» Octanoylcarnitine, Oct

» Pyruvate, P

» Succinate, S

Glossary

» List of SUIT states

» SUIT concept

Strengths and limitations

• Comparison of GM- with PM-capacity yields important information on N-pathway respiratory control upstream of CI (Lemieux et al. 2017; Votion et al. 2012).
• A succinate concentration of >10 mM may be required for saturating SE capacity.
• Rox might be inhibited slightly further by inhibition of CIV by cyanide (KCN; 1 μM). But cyanide inhibits not only CIV, but also catalase and other oxygenases involved in ROX.

+ NS-OXPHOS capacity provides a physiologically relevant estimate of maximum mitochondrial respiratory capacity.

+ Glutamate is easier to prepare compared to pyruvate.

+ Application of the cytochrome c test early in the protocol ensures comparability of all states in case of any effect of c.

+ Reasonable duration of the experiment.

- GM and PM yield typically identical fluxes in human skeletal muscle fibres. However, PM is the superior alternative to GM: the fraction of the N-pathway is lower and of the S-pathway is higher with GM compared to PM (GM_P is inhibited by the CII inhibitor malonic acid to a larger extent than PM_P). PM, therefore, yields a more sensitive assay for the diagnosis of injuries in the N-pathway, since an impairment of N-pathway capacity can be compensated partially by activation of the S-pathway. This is a disadvantage compared to SUIT-004 and SUIT-008 for diagnosis of N-capacity.

- To detect an additive effect of P after GM_P, pyruvate would have to be added as step 3 (before S). However, inhibition of respiration was observed after titration of P (5 mM) in horse skeletal muscle fibres (Votion et al 2012), which was not the case when P was titrated in steps of 1 mM.

- When evaluating the additive effect of the N- and S-pathway, it has to be considered that NS_P- and NS_E-capacities can only be compared with N_P- and S_E-capacities. This is not a problem when NS_P = NS_E (Gnaiger 2009). Otherwise, it may be assumed that S_P = S_E (Votion et al 2012), such that NS_P can be compared with N_P + S_P. SUIT-004 should be chosen for the additive effect in the ET-state.

- Rox may be lower in substrate states earlier in the SUIT protocol. Therefore, this Rox measurement is frequently taken as a methodological control rather than as the final basis of Rox correction of mitochondrial respiration (mt).

- Careful washing is required after the experiment to avoid carry-over of inhibitors and uncoupler.

- CIV activity is not measured, to save experimental time.

Compare SUIT protocols

• GM and PM yield typically identical fluxes in human skeletal muscle fibres.
• SUIT-004 1PM;2D;3U;4S;5Rot-: SUIT-004 allows the evaluation of the linear coupling control (L- P) with PM (instead of GM) as NADH linked-substrates. Moreover, in SUIT-004 the linear coupling control from P to E (with PM) and the ET-pathway state in NS- and S-pathways can be assessed.
• SUIT-008 1PM;2D;3G;4S;5U;6Rot-: SUIT-008 protocols are designed to assess the additivity between the N- and S-pathway in the Q-junction, providing a physiologically relevant estimate of maximum mitochondrial respiratory capacity.
• SUIT-001 1PM;2D;3U;4G;5S;6Oct;7Rot;8Gp-: SUIT reference protocol 1 (RP1)gives information of the linear coupling control (L- P- E) with NADH linked-substrates (PM). Moreover, the pathway control in ET state (N, NS, FNS, S and SGp pathways) can be evaluated by using this SUIT protocol.
• SUIT-028: PGM as NADH linked-substrates.

References

MitoPedia concepts: MiP concept, SUIT protocol, Recommended 

MitoPedia methods: Respirometry