respiratory state

or state of the respiratory chain

any one of the possible steady states of the phosphorylating respiratory chainin mitochondria. In state 1 both ADP and respiratory instrates are lacking. State 2 is a 'standard state' in which ADP has been added to exhaust the endogenous respiratory instrate; in state 2′ instrate has been added to exhaust the endogenous ADP. In state 3, the 'active' state of rapid respiration, all required components are present and the respiratory chain itself is the rate-limiting factor. State 4, an anaerobic 'resting' state, is characterized by a low respiration rate. In state 5, only oxygen is lacking, the respiration rate then being at zero.

State	[O2]	[ADP]	Sustrate level	Respiration Rate	Rate-limiting factor
1	>0	low	low	slow	ADP
2	>0	high	0	slow	substrate
2′	>0	low	high	slow	ADP
3	>0	high	high	fast	respiratory chain
4	>0	low	high	slow	ADP
5	0	high	high	0	O2

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