Kinetics

Dietary pantothenic acid occurs primarily in the form of acyl proteins, CoA or pantotheine 4'-phosphate, which are converted into pantetheine in the intestinal lumen. Pantetheine is converted to pantothenic acid by pantetheine hydrolase (EC 3.5.1.92) also found in the intestinal lumen.166 Enteric bacteria can also provide a source of CoA and pantetheine 4'-phosphate; however, the importance of this source is not known. Pantothenic acid is absorbed from the intestine, more in the jejunum than the ileum, through the sodium-dependent multivitamin transporter (SMVT), which also transports biotin and lipoic acid.141,148 This explains the ability of these three substances to competitively inhibit absorption of each other. The transporter is driven by the Na+ gradient that exists from the extracellular fluid to the intracellular fluid, transporting 2 Na+ for each monovalent anion of pantothenate, biotin, or lipoate.167 In addition, the inside-negative membrane potential may also act as a driving force because a net charge of +1 enters the cell.

This same carrier is ubiquitous throughout bodily tissues and probably also accounts for cellular uptake from the blood. Conversion to the active form, acetyl-CoA, most likely occurs inside the cell.

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