So after hexokinase, phosphofructokinase 1 is like our 2nd most influential enzyme on glycolysis. And it, you might remember, catalyzes that commitment step to glycolysis when you burn your second ATP to phosphorylate the molecule a second time, right? So just to, you know, be crystal clear here. I'm sorry if this is a review but you know, as soon as glucose enters the cell, it's turned into glucose 6 phosphate regardless of what it's going to go on to do. But if you're going to commit to glycolysis, that's where phosphofructokinase comes in, right? That's that commitment step to glycolysis. Glucose 6 Phosphate can do other things but once PFK is done, it’s glycolysis time. Anyways, so this, you know, it should make sense then that phosphofructokinase is like the 2nd most influential enzyme on glycolysis, on the rate of glycolysis. It actually has allosteric regulatory sites that bind ATP and hopefully, you know, you just guess that well, ATP is the product, right, the downstream product so I bet ATP is going to have an inhibitory effect and you betcha. High ATP concentrations lower enzyme activity. Citrate actually will also inhibit PFK 1. Citrate, you might recall the first molecule formed in the citric acid cycle. It is actually an important molecule for biosynthesis and it will be transported out into the cytoplasm, right? Citrate is going to be produced in the mitochondrial matrix but it's transported out into the cytoplasm to undergo biosynthesis And, if it is in excess concentrations, it'll inhibit PFK1 and and you know, let's think about this logically. If the citric acid cycle is going gangbusters, right? It's overproducing. It's going to filter off some citrate to do biosynthesis with. It's like we don't need all these, right? We're doing we're making too much so let's filter some off back in the cytosol, do biosynthesis but if you're filtering off a lot, you're going to really build up a lot of citrate
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism
Metabolic Regulation 2