{"id":686,"date":"2017-10-26T15:45:37","date_gmt":"2017-10-26T15:45:37","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/sunynutrition\/?post_type=chapter&p=686"},"modified":"2017-11-14T15:38:28","modified_gmt":"2017-11-14T15:38:28","slug":"9-32-enzymatic-functions","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-herkimer-nutritionflex\/chapter\/9-32-enzymatic-functions\/","title":{"raw":"9.32 Enzymatic Functions","rendered":"9.32 Enzymatic Functions"},"content":{"raw":"
\r\n\r\nIn addition to its antioxidant function, vitamin C is also a cofactor for a number of enzymes. The enzymes proline hydroxylase and lysyl hydroxylase are important in the formation of the protein collagen. Hydroxylase means that the enzymes add alcohol (hydroxyl, -OH) to the amino acids proline and lysine, as shown below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1064\"]\"\" Figure 9.321 Proline hydroxylase adds an alcohol group (circled) to proline forming hydroxyproline1,2[\/caption]\r\n\r\n<\/div>\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1091\"]\"\" Figure 9.322 Lysyl hydroxylase adds an alcohol group (circled) to lysine forming hydroxylysine3,4[\/caption]\r\n\r\n<\/div>\r\nAs shown below, proline and lysyl hydroxylases require ferrous iron (Fe2+) to function. But in the course of the hydroxylating proline or lysine, ferrous iron (Fe2+) is oxidized to ferric iron (Fe3+). Ascorbic acid is required to reduce Fe3+ to Fe2+, forming semidehydroascorbic acid in the process. With Fe2+, the enzyme is then able to continue to hydroxylate proline and lysine.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"865\"]\"\" Figure 9.323 Ascorbic acid reduces iron so that it can continue to serve as a cofactor for proline and lysyl hydroxylases[\/caption]\r\n\r\n<\/div>\r\nWhy should you care about collagen formation? Because collagen is estimated to account for 30% or more of total body proteins5<\/sup>. Collagen contains a number of hydroxylated prolines and lysines that are needed for collagen strands to properly cross-link. This cross-linking is important for collagen to wind together like a rope, forming the strong triple helix known as tropocollagen. This process is shown in the following animation, as well as in the figure below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1125\"]\"\" Figure 9.324 Production of cross-linked tropocollagen in the presence of adequate vitamin C[\/caption]\r\n\r\n<\/div>\r\nBut if there isn't enough ascorbic acid available, the collagen strands are underhydroxylated and instead of forming strong tropocollagen, the underhydroxylated collagen is degraded as shown below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1112\"]\"\" Figure 9.325 Production of underhydroxylated collagen[\/caption]\r\n\r\n<\/div>\r\nThis weak collagen then results in the symptoms seen in the vitamin C deficiency, scurvy, that will be discussed in the next subsection.\r\n\r\nAscorbic Acid is also needed for:\r\n\r\nCarnitine synthesis\r\n\r\nTyrosine synthesis and catabolism\r\n\r\nSerotonin (neurotransmitter) synthesis\r\n\r\nOther hormone and neurotransmitter synthesis6<\/sup>\r\n\r\nThe figure below shows how ascorbic acid is needed for dopamine hydroxylase, which ultimately produces the hormone epinephrine.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"264\"]\"\" Figure 9.326 Dopamine beta-hydroxylase requires ascorbic acid to produce norepinephrine[\/caption]\r\n\r\n<\/div>\r\nReferences & Links<\/b>\r\n\r\n1. https:\/\/en.wikipedia.org\/wiki\/Proline#\/media\/File:Prolin_-_Proline.svg\r\n\r\n2. http:\/\/en.wikipedia.org\/wiki\/File:Hydroxyproline_structure.svg\r\n\r\n3. https:\/\/en.wikipedia.org\/wiki\/Lysine#\/media\/File:L-lysine-monocation-2D-skeletal.png\r\n\r\n4. http:\/\/en.wikipedia.org\/wiki\/File:Hydroxylysine.png\r\n\r\n5. Di Lullo G, Sweeney S, Korkko J, Ala-Kokko L, San Antonio J. (2002) Mapping the ligand-binding sites and disease-associated mutations on the most abundant protein in the human, type I collagen. The Journal of Biological Chemistry 277(6): 4223-4231.\r\n\r\n6. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.\r\n\r\n7. http:\/\/en.wikipedia.org\/wiki\/File:Catecholamines_biosynthesis.svg\r\n\r\n<\/div>","rendered":"
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In addition to its antioxidant function, vitamin C is also a cofactor for a number of enzymes. The enzymes proline hydroxylase and lysyl hydroxylase are important in the formation of the protein collagen. Hydroxylase means that the enzymes add alcohol (hydroxyl, -OH) to the amino acids proline and lysine, as shown below.<\/p>\n

\n
\"\"<\/p>\n

Figure 9.321 Proline hydroxylase adds an alcohol group (circled) to proline forming hydroxyproline1,2<\/p>\n<\/div>\n<\/div>\n

\n
\"\"<\/p>\n

Figure 9.322 Lysyl hydroxylase adds an alcohol group (circled) to lysine forming hydroxylysine3,4<\/p>\n<\/div>\n<\/div>\n

As shown below, proline and lysyl hydroxylases require ferrous iron (Fe2+) to function. But in the course of the hydroxylating proline or lysine, ferrous iron (Fe2+) is oxidized to ferric iron (Fe3+). Ascorbic acid is required to reduce Fe3+ to Fe2+, forming semidehydroascorbic acid in the process. With Fe2+, the enzyme is then able to continue to hydroxylate proline and lysine.<\/p>\n

\n
\"\"<\/p>\n

Figure 9.323 Ascorbic acid reduces iron so that it can continue to serve as a cofactor for proline and lysyl hydroxylases<\/p>\n<\/div>\n<\/div>\n

Why should you care about collagen formation? Because collagen is estimated to account for 30% or more of total body proteins5<\/sup>. Collagen contains a number of hydroxylated prolines and lysines that are needed for collagen strands to properly cross-link. This cross-linking is important for collagen to wind together like a rope, forming the strong triple helix known as tropocollagen. This process is shown in the following animation, as well as in the figure below.<\/p>\n

\n
\"\"<\/p>\n

Figure 9.324 Production of cross-linked tropocollagen in the presence of adequate vitamin C<\/p>\n<\/div>\n<\/div>\n

But if there isn’t enough ascorbic acid available, the collagen strands are underhydroxylated and instead of forming strong tropocollagen, the underhydroxylated collagen is degraded as shown below.<\/p>\n

\n
\"\"<\/p>\n

Figure 9.325 Production of underhydroxylated collagen<\/p>\n<\/div>\n<\/div>\n

This weak collagen then results in the symptoms seen in the vitamin C deficiency, scurvy, that will be discussed in the next subsection.<\/p>\n

Ascorbic Acid is also needed for:<\/p>\n

Carnitine synthesis<\/p>\n

Tyrosine synthesis and catabolism<\/p>\n

Serotonin (neurotransmitter) synthesis<\/p>\n

Other hormone and neurotransmitter synthesis6<\/sup><\/p>\n

The figure below shows how ascorbic acid is needed for dopamine hydroxylase, which ultimately produces the hormone epinephrine.<\/p>\n

\n
\"\"<\/p>\n

Figure 9.326 Dopamine beta-hydroxylase requires ascorbic acid to produce norepinephrine<\/p>\n<\/div>\n<\/div>\n

References & Links<\/b><\/p>\n

1. https:\/\/en.wikipedia.org\/wiki\/Proline#\/media\/File:Prolin_-_Proline.svg<\/p>\n

2. http:\/\/en.wikipedia.org\/wiki\/File:Hydroxyproline_structure.svg<\/p>\n

3. https:\/\/en.wikipedia.org\/wiki\/Lysine#\/media\/File:L-lysine-monocation-2D-skeletal.png<\/p>\n

4. http:\/\/en.wikipedia.org\/wiki\/File:Hydroxylysine.png<\/p>\n

5. Di Lullo G, Sweeney S, Korkko J, Ala-Kokko L, San Antonio J. (2002) Mapping the ligand-binding sites and disease-associated mutations on the most abundant protein in the human, type I collagen. The Journal of Biological Chemistry 277(6): 4223-4231.<\/p>\n

6. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.<\/p>\n

7. http:\/\/en.wikipedia.org\/wiki\/File:Catecholamines_biosynthesis.svg<\/p>\n<\/div>\n\n\t\t\t

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Candela Citations<\/h3>\n\t\t\t\t\t
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