Heme: Introduction

00:02 In another set of these lectures, I've talked about the importance of heme for carrying oxygen within hemoglobin.

00:08 In these set of lectures, I'll talk about how that heme is made and how the iron in the heme is transported and stored in the body.

00:17 Now, heme is as you've seen in the other lectures, a flat, planar structure that contains a porphyrin ring with an atom of iron at its very center.

00:26 The ring structures that hold the iron can serve as a sink for electrons and this can be valuable also for the process of electron transport.

00:35 The ring also enables the carrying of oxygen which is what happens inside of hemoglobin.

00:40 So, hemes are usually found attached to proteins.

00:43 That's true whether they're in the electron transport system or they're contain within a hemoglobin or myoglobin.

00:49 The examples, of course, include these proteins: hemoglobin, myoglobin and the cytochromes of the electron transport system.

00:56 The names of the cytochromes in the electron transport system come from the hemes that they contain.

01:01 Cytochrome a, for example contains heme a.

01:05 The ring structure that's found in the hemes of hemoglobin, myoglobin and cytochromes is also found in the chlorophyll.

01:13 And in the chlorophyll, the ion is replaced with the magnesium at its center.

01:17 The cobalamins, also known as vitamin B12, have a cobalt at their center instead and we can see that here.

01:24 Now, the structure and function of hemes is related to their planar structure.

01:28 And we can see that the various hemes have a very similar central structure as we see in Heme A, Heme B , Heme C and Heme D.

01:37 And we see that the primary differences of these different forms of heme are due to alterations on the outer part of the molecule.

01:43 These have little effect on the function of each of the individual hemes.

01:48 Heme A is found as part of the complex IV of the electron transport system and it’s the part where oxygen is reduced.

01:56 Heme B is the most common type that we see and it's found in hemoglobin, myoglobin, peroxidase enzymes and cycloxygenase enzymes for making prostiglandins.

02:05 Other proteins that contain heme B include the P450 hydroxylation system of the liver and the nitric oxide synthase system that we've talked about in other lectures.

02:15 Now heme C is found as the name would suggest in cytochromes C, a very important protein in the electron transport system.

02:22 And it links to the protein via cysteines, the sulfur side chains.

02:27 Heme O functions in bacterial oxygen reduction very much like the heme A does where the complex IV reduces oxygen.