{"id":6873,"date":"2021-09-15T18:02:03","date_gmt":"2021-09-15T16:02:03","guid":{"rendered":"https:\/\/meddists.com\/learn\/?page_id=6873"},"modified":"2021-09-16T13:16:52","modified_gmt":"2021-09-16T11:16:52","slug":"shuttles-in-order-to-support-glycolysis","status":"publish","type":"page","link":"https:\/\/meddists.com\/learn\/pre-clinical\/biochemistry\/biochemistry-of-the-metabolism\/carbohydrate-metabolism\/shuttles-in-order-to-support-glycolysis\/","title":{"rendered":"Shuttles to support glycolysis"},"content":{"rendered":"\n

Shuttle reactions are supporting glycolysis\/mitochondrial ATP production.<\/p>\n\n\n\n

There are three shuttle pathways to transport reducing equivalents to mitochondria:
1. Glycerol Phosphate shuttle
2. Malate-Aspartate shuttle
3. Lactate shuttle<\/strong><\/p>\n\n\n\n

<\/div><\/p>\n\n\n\n

Glycerol Phosphate Shuttle<\/h2>\n<\/span>\n\n\n
\"\"<\/a>
Figure 1. Glycerol-phosphate shuttle<\/strong><\/figcaption><\/figure><\/div>\n\n\n\n

The glycerol-3-phosphate shuttle is a mechanism that regenerates NAD+<\/sup> from NADH, as a side product during glycolysis (Figure 1<\/strong>).<\/p>\n\n\n\n

NADH is oxidised in the mitochondria but is not transported through the inner membrane, so it is delivered through transport systems. <\/p>\n\n\n\n

Glycerol phosphate dehydrogenase (GPD) is also found in the cytosol and on the mitochondrial membrane and catalyzes the conversion of dihydroxyacetone phosphate into glycerol phosphate.
<\/p>\n\n\n\n

Cytoplasmic <\/strong>GPD converts dihydroxyacetone phosphate to glycerol 3-phosphate by oxidizing one molecule of NADH to NAD+<\/sup>.<\/p>\n\n\n\n

Glycerol-3-phosphate gets converted back to dihydroxyacetone phosphate by an inner membrane-bound mitochondrial<\/strong> GPD by one molecule of enzyme-bound FAD to FADH2<\/sub>. (FADH2<\/sub> then reduces coenzyme Q which enters into oxidative phosphorylation)<\/em><\/p>\n\n\n<\/span>\n

Malate – Aspartate Shuttle<\/h2>\n<\/span>\n\n\n

This shuttle is required because the mitochondrial inner membrane is not permeable to NADH. To solve this, malate carries the reducing equivalents across the membrane by a change into oxaloacetate (OXA).<\/p>\n\n\n\n

\"\"<\/a>
Figure 2. Malate – Aspartate shuttle<\/strong><\/figcaption><\/figure><\/div>\n\n\n\n

The system works with the malate dehydrogenase enzyme<\/strong><\/p>\n\n\n\n

NADH is oxidised to NAD+<\/sup><\/strong>, and oxalacetate is reduced to malate<\/strong> which can already be transported to the mitochondria where oxalacetate is oxidized, and NAD+<\/sup> is returned to NADH + H+<\/sup>.<\/p>\n\n\n\n

OXA<\/strong>, however, cannot return \u2014 therefore, it should be<\/strong> either reduced<\/strong> to malate or transaminated to aspartate<\/strong><\/p>\n\n\n\n

<\/p>\n\n\n<\/span>\n

Lactate Shuttle<\/h2>\n<\/span>\n\n\n

The two NADH are transferred to the mitochondrial electron transport chain, and the pyruvate is broken down into the citrate circuit to produce\u00a030 ATPs<\/strong>, resulting in\u00a036-38 ATPs<\/strong>\u00a0from glucose. Anaerobic glycolysis will only produce 2 ATPs<\/strong>, generating lactate<\/strong>. <\/p>\n\n\n\n

Lactate shuttle works with NADH transport, based on the cytosolic and mitochondrial activity of lactate dehydrogenase. Lactate is eliminated by gluconeogenesis in the liver and by the lactate shuttle in the mitochondria. The lactate can move freely between cell and tissue compartments, by the help of Mono- Carboxylate-Transporters (MCT) (Figure 3).<\/p>\n\n\n\n

\"\"<\/a>
Figure 3. Lactate shuttle<\/strong><\/figcaption><\/figure>\n\n\n<\/span>\n

References<\/h2>\n<\/span>\n\n\n

Snider MDS. Devlin\u2019s Textbook of Biochemistry with Clinical Correlations<\/strong>, the 8th Edition. John Wiley & Sons, Incorporated, 2020; 2019.<\/span> <\/p>\n<\/span>

Glycerol Phosphate Shuttle<\/h2>

Malate – Aspartate Shuttle<\/h2>

Lactate Shuttle<\/h2>

References<\/h2><\/div>","protected":false},"excerpt":{"rendered":"

Glycerol Phosphate Shuttle The glycerol-3-phosphate shuttle is a mechanism that regenerates NAD+ from NADH, as a side product during glycolysis (Figure 1). NADH is oxidised in the mitochondria but is not transported through the inner membrane, so it is delivered through transport systems. Glycerol phosphate dehydrogenase (GPD) is also found in the cytosol and on […]<\/p>\n","protected":false},"author":23,"featured_media":0,"parent":1711,"menu_order":6,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-6873","page","type-page","status-publish","hentry"],"yoast_head":"\nShuttles to support glycolysis – Meddists<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/meddists.com\/learn\/pre-clinical\/biochemistry\/biochemistry-of-the-metabolism\/carbohydrate-metabolism\/shuttles-in-order-to-support-glycolysis\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" 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