Isotopically-labeled substrates were incubated incubated with suspensions from r
ID: 967411 • Letter: I
Question
Isotopically-labeled substrates were incubated incubated with suspensions from respiring muscle tissue poisoned with malonate, blocking the citric acid cycle at reaction 6, succinate dehydrogenase. If the tricarboxylic acid cycle intermediates listed below are isolated, predict which carbon atoms of the isolated products would be expected to be labeled. Substrate is^14CH_3COCOOH with excess unlabeled oxaloacetate added. Products isolated are (1) isocitric acid, (2) a-ketoglutaric acid, (3) succinic acid. Substrate is^14CH_3COCOOH. Product is (1) isocitric acid, (2) a-ketoglutaric acid, (3) succinic acid. Substrate is H^14CO_3 Product is (1) isocitric acid, (2) a-ketoglutaric acid, (3) succinic acid, (4) malic acid. Substrate is 5-^14 C-fructose. Product is (l)isocitric acid, (2) succinic acid.Explanation / Answer
Aconitase
14CH3COCOOH + COOHCOCH2COOH COOH14CH2CHCOOCHOHCOOH
Pyruvic acid Oxaloacetate H2O Isocitrate
H+
CO2 Isocitrate DH
COOH14CH2CH2COCOOH
- Keto glutarate
-keto glutrate fumarase
DH
COOH14CH2CH2COCOOH COOH14CH2CH2COOH COOH14CH2CH2COOH
- Keto glutarate Succinic acid Malic acid
Isotopically radio labelled isotopes incubated with suspensions from respiring muscle tissue poisoned with malonate block the citric acid cycle, radio labelled isotopes transfers their carbon atoms to 2 carbon atom. Fructose formed in gluconeogenesis cycle in the same way 2 carbon only.
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