Chapter 9. Vitamins, Hormones, Minerals, Drugs, And Equipment For Certain Lab Tests

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Vitamins

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necessary in trace amounts for normal body function. There are water soluble vitamins : b1,2,6,12, C, folacin, biotin, niacin, and pantothenate AND fat-soluble vitamins: A, D, E, and K.

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Vitamin B1 (Thiamine)

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Thpp (thiamine pyrophosphate), prosthetic group for 2-ketoglutarate dehydrogenase, pyruvate dehydrogenase, and transketolase. Measure red cell transketolase activity as index for deficiency.

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Vitamin B2 (riboflavin)

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Acts as coenzyme FAD (flavin adenine nucleotide) and FMN (flavin mononucleotide). Used in redox rx. (ie in chain of electron transport and cytochrome P450 hydroxylase system. FAD-->FADH2 and FMN-->FMNH2. Also riboflavin is component of succinate dehydrogenase and acyl CoA dehydrogenase.

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Vitamin B6 (pyridoxine, pyridoxal, and pyridoxamine)

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Prosthetic group for all transaminases. Pyruvate (C3) + glutamate-->alanine + 2-ketoglutarate. OR 2-ketoglutarate + aspartate --> oxaloacetate + glutamate.OR histidine --> histamine. OR homocysteine + serine --> cystathionine.

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Vitamin B12 (Cobalamin)

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Resembles porphyrins in structure, but has a cobalt ion in its center. It is used for: 1 .Rearrangements (Methylmalonyl CoA-->succinyl CoA) or 2. Methylation (Homocysteine-->methionine). Methyl malonic acid is indicator for B12 deficiency. Blood homocysteine may rise with B12 or folate deficiency.

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Intrisic Factor

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Glycoprotein, produced in stomach (facilitates transport of B12 from gut to general circulation).

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Vitamin C

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Conversion of collagen proline to collagen hydroxyproline. This antioxidant products molecules from oxidation. It's a reducing agent, so it can reduce iron to Fe++ to aid absorption. (Proline (and lysine)--> hydroxyproline/hydroxylysine. Tyrosine-->homogentisic acid. Also, plays a role in synthesis of norepinephrine from dopamine.

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Folate/folic acid/(folacin)

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Precursor of tetrahydrofolate (THF), a 1-carbon donor in biochemistry rx. Tetrahydrofolate, an important methyl group is important in formation of purines and pyrimidines (DNA synthesis). (Glycine-->serine and homocysteine-->methionine (B12 for that last one too). Note B12 and folacin are both important in rapidly dividing cells (ie bone marrow).

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A defieicny in B12 or folacin results in:

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Megaloblastic anemia

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Biotin

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Coenzyme for carboxylases, and it carries activated CO2. (Ex: pyruvate-->oxaloacetate. Acetyl CoA-->malonyl CoA. Propionyl CoA-->Methylmalonyl CoA).

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Niacin (Nicotinic Acid)

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Part of NADH and NADPH molecules. Produced from essential amino acid tryptophan.

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Pantothenic acid

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Part of CoA molecule (aka acetyl CoA, malonyl CoA, and succinyl CoA), and a part of the acyl carrier protien of fatty acid biosynthesis.

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Vitamin A (retinol)

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Fat soluble. Part of rhodopsin in retina and cone photoreceptor pigment iodopsin. Maintain skin/mucosa. Perhaps an antiproliferate hormone-->resuilting in gene expression alteration.

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Vitamin D

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Sunlight striking skin signals production, hormone-like. Raises blood levels of calcium and phosphorus. Promotes calciuma nd phosphorus transfer from bone to blood; promotes calcium retention in kidney. Can act as a hormone by entering cell nucleus and interacting with DNA to regulate protein synthesis via Vit D receptor.

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Vitamin E

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Appears to act as antioxidant. Contributes electrons to lipids (free radical form) stabilizing/protecting them from oxidation.

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Vitamin K

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Produced by plants (k1) and bacteria (k2). Necessary for production of prothrombin and clotting factors in the liver. Coenzyme for carboxylation of several clotting factors.

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Hormones

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Produced in the body, can travel in blood stream, are not coenzymes, but do modify the actions of enzymes. We generally consider hormones to have a more profound effect on body than vitamins with slight blood level change. Can be proteins (oxytocin, TSH, insulin) others can be derivatives of amino acids (thyroxine, epinephrine), others (steroids) are produced in lipidland as cholesterol derivatives. Hormones affect rate of synthesis of proteins (such as enzymes), activity of enzymes, or permeability of cell membrane.

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Second messengers of clinical importance:

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cAMP, cGMP, inositol triphosphate, diglyceride, and Ca++.

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Insulin second messenger

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action of insulin doesn't appear to be mediated by cAMP.

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Steroid hormones

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Act on cytoplasmic receptors, resulting in complex moving to nucleus to influence DNA transcription. Thyroid hormone directly enters nucleus, altering DNA. Epinephrine has two receptors (alpha and beta) with alpha producing vasoconstriction and beta 2 producing vasodilation.