Control of Fat Metabolism

by Kevin Ahern, PhD

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    00:00 Now the hormonal systems that I have talked about it, epinephrine, glucagon and insulin that apply for the sugar metabolism also apply for a fat metabolism in ways that you could probably predict, as we will see.

    00:13 Let's start with the epinephrine glucagon stimulation of that same cell and understand what happens to fat metabolism.

    00:21 The hormone binds first and that causes the G protein to be activated.

    00:24 We see the activation of the adenylate cyclase to make cyclic AMP.

    00:29 The cyclic AMP interacts with protein kinase A to activate it.

    00:34 Now in this case what protein kinase A is phosphorylating, is an enzyme that's essential for the breakdown of fat.

    00:42 In the breakdown of fat, the most important enzyme is an enzyme known as triacylglycerol lipase.

    00:48 And like the glycogen breakdown enzymes, phosphorylating it favors its activity. Now triacylglycerol lipase works in conjunction with another protein called perilipin and the phosphorylation of it also favors the breakdown of fat.

    01:07 Now we see that happening below where the triacylglycerol fat is being converted into a diacylglycerol and then beneath that you see the other lipases.

    01:15 Well, what those lipases are doing, is that they are breaking fatty acids off of the triacylglycerol.

    01:22 Once the first fatty acid is removed from the triacylglycerol to make the diacylglycerol, then the other enzymes that breakdown the diacylglycerol, don't require the regulation.

    01:36 So in this way the phosphorylation cascade that's made by the binding of epinephrine or glucagon is favoring the release of fatty acids or the breakdown of fat.

    01:46 The other by product of the breakdown of fat, of course, is glycerol, as can be seen here.

    01:52 So non-regulated enzymes don't require phosphorylation and as a consequence, fat is broken down.

    02:00 Now when insulin binds to the cell surface receptor not surprisingly, we are going to see exactly the opposite thing happen.

    02:07 When insulin bind to the receptor there is our friend phosphoprotein phosphatase, it is activated. It will take phosphates off of the proteins that had phosphates put onto them earlier.

    02:20 In addition there is an important protein that's necessary and important enzyme is necessary for the synthesis of fatty acids.

    02:26 This enzyme is known as acetyl-CoA-carboxylase and this enzyme is regulated by phosphorylation.

    02:34 In the phosphorylated state that enzyme is inactivated.

    02:40 So the removal of a phosphate from acetyl-CoA-carboxylase causes it to become active.

    02:46 Well when acetyl-CoA-carboxylase is activated what it does, is it makes fatty acids.

    02:53 And when you start making fatty acids they start getting attached to glycerol.

    02:58 And when they start getting attached to glycerol, you make fat.

    03:01 Well on the other side of this, what the removal of phosphates is doing from these enzymes is triacylglycerol lipase, the enzyme that broke down the fat in the first phase has it's phosphate removed, as does the perilipin.

    03:16 These two then become inactive so fat no longer is being broken down.

    03:23 Under conditions of insulin stimulation, what's happening is the body is making fat and it has stopped the breakdown of the same fat.

    About the Lecture

    The lecture Control of Fat Metabolism by Kevin Ahern, PhD is from the course Metabolic Control.

    Included Quiz Questions

    1. Insulin and adrenaline together participate in the breakdown of proteins inside the cell by regulating the phosphorylation of proteases
    2. The binding of epinephrine or glucagon to the cell receptors, stimulate the breakdown of fats by activating the triacylglycerol lipase enzyme
    3. The attachment of insulin to the cell membrane receptor activates the enzyme phosphoprotein phosphatase and stimulates the removal of phosphate from the activated triacylglycerol lipase and perilipin protein
    4. Insulin works against the adrenalin hormone and stimulates the fat synthesis in the body
    5. The phosphorylated triacylglycerol lipase works in conjugation with perilipin protein and removes the first fatty acid from the triacylglycerol molecule
    1. Acetyl-CoA-carboxylase
    2. Perilipin
    3. Triacylglycerol lipase
    4. Glycogen synthase
    5. Phosphoglucomutase

    Author of lecture Control of Fat Metabolism

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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