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Niacin: Metabolism to NAD and NADP

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⚡ Welcome to Catalyst University! I am Kevin Tokoph, PT, DPT.

Welcome back to vitamins in biochemistry on catalyst university my name is kevin toka make sure to like this video and subscribe to the channel for future videos and notifications we’re going to talk about vitamin b3 in this video which is also known as niacin when that structure of nice and is shown here below so here’s a main difference between niacin that we

Don’t observe in other vitamins so unlike thiamine riboflavin pantothenate pyridoxine foley and cobalamin which are the other b vitamins niacin can be synthesized de novo in humans okay there’s a pathway we have to do it it’s not super efficient but it can be done okay this structure right here obviously of niacin is not the active bio it’s not the bioactive

Coenzyme we’re going to have to transform it into nad or nad p for it to become activated so a process that we’re going to use to do that is going to be a maday ssin and then subsequent ribosylation and then ad emulation and that’s going to give us the structure we know as nad but here’s what we’re going to do here we’re going to focus on this pathway up here and

This one over here we’re looking at what’s called the de novo pathway first and then we’re going to see how it converges with the pathway that we use from the diet it turns out that tryptophan breakdown when we start doing catabolism of tryptophan which isn’t as common because we don’t usually preferentially catabolized essential amino acids the only way we really

Do that is if there’s excess of them and we don’t really need to have them around but for the average person we don’t really do much of that so we can make it de novo but it really is definitely getting through the diet the point is we can do it but when tryptophan is being broken down we get down to this metabolite called quinna linic acid quinol inuk acid is

One of these molecules that really shouldn’t form it is a it is a side reaction of another molecule that was previously formed it’s a product of that side reaction it turns out there’s an enzyme that’s named for this reaction because it’s that important it’s those quinol inuk acid fluoride as you’ll transferase it’s going to use prpp it’s going to attach a ribose

5-phosphate ultimately to this corner linic acid but at the same time it’s going to decarboxylate one of those carboxyl groups so you get this molecule which is called nicotinic mononucleotide okay nicotinic mononucleotide is where we converge with dietary niacin which is shown here this is niacin niacin is going to react with nicotinic phosphorus you’ll transferase

Another prpp dependent enzyme that’s going to attach the ribose 5-phosphate to this it doesn’t need to do that extra decarboxylation because niacin or nicotine 8 only has one carboxyl group either way we converge at nicotine eight mononucleotide nicotine eight mononucleotide is going to react with nicotine eight mononucleotide adenosyl transferase that’s going

To catalyze the adem elation of nicotine eight mononucleotide to form dm id o nad alright this is almost nad but nad has that amide group that’s here and set this should be an amide right here not a carboxyl so as a result of this we call this molecule dm id o nad it turns out that dmi toh nad must be a maday ‘td and that’s going to be catalyzed by a dmi – nad a

Myto transferase okay the amide group is going to come from glutamine a glutamine hydrolyzing enzyme and when we amma date dm i know nad we get nad okay it turns out that nad can be phosphorylated further by nad kinase to get nad p it turns out there is it also another pathway down here referred to as the salvage pathway suppose we start with nad but this entire

Adp group gets removed somehow maybe through hydrolysis in fact they could be through a diet in the stomach that that happens we will get this molecule called ribose eel niacinamide okay right this can react with riotous eel niacinamide kinase to get n mn what this is called is niacin amide mononucleotide it turns out that niacin amide mononucleotide can then be

Identify niacin amide mononuclear a dental eel transferase which then takes that a mp group and puts it on this to make nad nad is the active form of this okay if it’s phosphorylated by nad kinase to make nad p nad p is also active all right now unlike f adn s mn which can transfer one or two electrons depending on the enzymes mechanism nad and nadp are required

To transfer to their limited and they transfer they accept and donate hydrides alright now one very important concept is how we detect nad are in aviation it turns out that we really don’t detect nad we actually detect nadh that’s sort of a requirement the reason for that this red dotted line is the absorption profile for nad the blue solid line is the absorption

Profile for nadh so it turns out that at 340 nanometers only nadh absorbs there there is no absorbance by nad there however if we try to absorb it to set absorbance at 260 nanometers nad and nadh absorb there to approximately the same amount nad absorbs a little more but there’s so much overlap there that it’d be worthless to try to measure absorbance at 260 so

We’re going to choose way out here at this particular local lambda max of 340 nanometers and we’re going to measure nadh and the reason we choose that is because nad has zero absorbance there so we can get a measure of nadh so it doesn’t matter what reaction the direction is running we’re always going to measure either the production of nadh or the disappearance of

Nadh or its consumption okay either way we do that if we want to measure an enzymes activity we can get the enzymes activity it doesn’t matter if nadh is being formed or consumed we can do various mathematical transformations to get the enzymes activity we’re always going to do 344 nicotinamide coenzymes all right so an example here’s a reaction that we have videos

On called lactate dehydrogenase this enzyme is going to convert el lactate to pyruvate and in doing so it’s going to take nad to oxidized el lactate into pyruvate but nad gets reduced to nadh now again my question is which one of these molecules up here would be best to measure absorbance up particularly using a uv-vis spectrophotometer well pyruvate and lactate

Don’t absorb and use eases nad and nadh both do but remember it’s not really worth our time to measure n abs absorbance it overlaps at every critical point that we could use but there is this point for nadh at 340 nanometers that there’s no overlap with nad so we’re always going to measure nadh as absorbance profile at 340 nanometers because there’s absolutely no

Competition from nad and by the way if you want more detailed information on electic dehydrogenase lab see the playlist on catalase university lactate dehydrogenase labs for biochemistry or cell biology labs and this is one of the important things just to remember nadh uniquely absorbs around 340 nanometers so the enzyme activity in other words the kinetics can be

Monitored and quantified by uv vis all right so hopefully this gave you a little bit of introduction on this particular b-vitamin and production to nad and nadp and how we can use it to do various things all right make sure to like this video and subscribe to the channel for future videos and notifications thank you very much

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Niacin: Metabolism to NAD and NADP By Catalyst University