Chapter 08 . Transport Across Membranes Chapter 7, Question 11 21 of 21> From th

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Chapter 08 . Transport Across Membranes Chapter 7, Question 11 21 of 21> From the figure below we know that exposed regions of membrane proteins can be labeled with 125 I by the lactoperoxidase (LP) reaction. Similarly carbohydrate side chains of membrane glycoproteins can be labeled with 'H by axidation of galactose groups with galactose oxidase (GO) followed by reduction with tritiated borohydride (H-BH4). Noting that both LP and GO are too large to penetrate into the interior of an intact cell explain each of the following observations made with intact erythrocytes. Lipid bilayer Hypotonic medium A Method for Labeling on One or Both Surfaces of a Membrane Vesicle. (a) When lactoperoxidase (LP) and 1251 are present in the solution outside a membrane vesicle, LP catalyzes the labeling of membrane proteins exposed on the outer membrane surface (ie., proteins A and B). If membrane vesicles are (b) first incubated in a hypotonic medium to make them permeable to LP and (c) then transferred to an isotonic solution containing 1251 but no external LP, proteins exposed on the inner membrane surface (i.e, proteins B and C) become labeled. Proteins Exposed Isotonic Lactoper Part A PartB When intact cells are incubated with GO and then reduced with H BH.several of the bands on the gel are found to be radioactive. Some of the membrane proteins associated with the outer phospholipid layer of the plasma membrane are lipoproteins, the fatty acid residues of which are accessible to the GO and borohydride. which is accessible to the GO and borohydride. which are accessible to the GO and borohydride. Some of the membrane proteins associated with the outer phospholipid layer of the plasma membrane are glycoproteins, the carbohydrate O Some of the membrane sterols associated with the outer phospholipid layer of the plasma membrane is cholesterol, the hydroxyl group of O Some of the membrane sterols associated with the outer phospholipid layer of the plasma membrane are phytosterols, the hydroxyl groups of side chains of which are accessible to the GO and borohydride. Part C This question will be shown after you complete previous question(s).

Explanation / Answer

Answer: Option D is correct.

Explanation: GO is too large to penetrate into RBC. So, it must act on the exposed carbohydrate moieties of glycoproteins located on the extracellular side of the lipid bilayer.

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