what are primary rate controlling enzyme of the energy producing metabolic pathways and cycles, including ATP-CP, glycolysis ,krebs cycle and ETC/

Answer 1

Your question is very broad, but here are some of the known true rate-limiting biochemical steps in metabolic pathways:

1. Glucose-6-phosphate dehydrogenase (G6PDH) catalyzing the forward reaction of glucose-6-phosphate to 6-phosphogluconolactone as the beginning of the pentose-phosphate pathway (which produces NADPH for anabolic function and leads to nucleotide biosynthesis)
2. Phosphofructokinase (PFK) 1 and 2 are rate limiting step for glycolysis, which is hormone responsive to insulin and glucagon
3. Pyruvate Kinase catalyzes the last step of glycolysis and is down-regulated by ATP and up-regulated by fructose-1,6-bisphosphate (F-1,6-BP)
4. Pyruvate dehydrogenase (PDH) catalyzes the transition of pyruvate from glycolysis into the TCA/Citric Acid/Kreb cycle and can be regulated by phosphorylation.
5. Succinyl-CoA synthase is the enzyme of a rate limiting step catalyzing succinate to succinyl-CoA (TCA cycle is inhibited if this is low)
6. Citrate lyase is a key enzyme for TCA as it catalyzes the oxaloacetate+acetyl CoA to citrate step, and low citrate halts the TCA cycle
7. Overall the TCA cycle is also inhibited by high ATP concentration
8. Biotin and acetyl-CoA carboxylase make up the limiting step for the conversion of acetyl-CoA to malonyl-CoA for fatty acid synthesis
9. Ornithine carbamoyl transferase (OCT) is a rate limiting step of the urea cycle catalyzing the reaction of ornithine + carbamoyl phosphate to citruline
10. CPT1 is another rate limiting step of fatty acid synthesis as it helps shuttle molecules across the selectively permeable mitochondrial membranes
11. HMG-Reductase is another rate limiting step of fatty acid synthesis and is a primary target of statin medications to reduce cholesterol production downstream
12. PRPP Synthase is a rate limiting step of the de novo purine synthesis pathway and is down regulated by AMP and GMP
13. Glucokinase/Hexokinase are down-regulated by glucose-6-phosphate
14. Finally glycogen phosphorylase is a regulating step of glycogenolysis that is up-regulated by glucagon, epinephrine, AMP, and calcium and is down-regulated by insulin and ATP concentration.