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22 Cards in this Set

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Is Mg micro or macro?
AI ~ 300-400mg range
nuts, legumes, whole grains
Where is Mg found internally?
99% is found w/in bones or intracellularly - it's the 2nd most abundant intracellular element behind K+
(60% bone/ 25% muscle)
1% in plasma 80% in free form
Absorption of Mg
Absorption occurs in the ileum and colon! Active absorption, ~30-40% absorbed.
How is Mg homeostatis maintained? (general)
Through urinary excretion: the amount of Mg reabsorped in the kidney determines amount excreted
What is the mechanism of Mg homeostatis?
80% plasma Mg filtered by kidney:
10-20% reabsorbed by proximal convoluted tubule
70-80% reabsorbed by "ascending limb of loop of Henle"
10% absorbed by distal convoluted tubule

** reabsorption is constant except in the ascending limb of loop of Henle. Regulation occurs here.
What are the metabolic roles of Mg?
Mg is involved in most aspects of metaboloism; 300+ enzymes.

Involved in enzyme systems in two ways:
• Mg/nucleotide complex: chelation of ATP lowers Ea for rate-limiting step of transphosphorylation
• allosteric activation of enzymes (direct binding)
Describe the complex between Mg and nucleotide substate
For example, ATP+Mg:
Mg interacts with the O's on the phosphate groups and with the N of the adenine: reduces negative charge cloud around ATP, lowering Ea of rxns
Name some enzymes that Mg binds with directly (allosteric activation)?
Adenylate cyclase!
Pyruvate kinase, phosphofructokinase
What are the signs of Mg deficiency?
The three hypo's: hypomagnesia, hypocalemia, hypokalemia. AND low circulating levels of PTH.
Describe the first stage of Mg deficiency? i.e. low mg causes what to happen?
Failure of heteroionic exchange of Ca/Mg in bone: plasma Ca concentrations down; PTH increases.
Describe the 2nd stage of Mg deficiency? i.e. low mg causes what to happen?
End organ PTH resistance develops:
Respons of end organs to PTH mediated by cAMP. Conversion of ATP-> cAMP is catalyzed by adenylate cyclase which is a Mg2+ dependent enzyme. Low intercellular Mg reduces amt of cAMP avaiable.

Osteoclasts less reponsive too.
Describe the 3rd stage of Mg deficiency? i.e. low mg causes what to happen?
PTH secretion drops; PTH levels in circulation drops. PTH secreption is cAMP dependent.
Describe the 4th stage of Mg deficiency? i.e. low mg causes what to happen?
Lack of PTH/cAMP prevents activation of Vitamin D; lack of Vitamin D prevents Ca absoroption. Lack of D and PTH prevents osteoclast precursur cells from stimulation into Osteoclasts.
Describe the 5th stage of Mg deficiency? i.e. low mg causes what to happen?
Lowered K+ reabsorption. Na,K-ATPase activity greatly reduced from lack of Mg.
What are the two ultimate causes of all of these problems?
- Lack of adenylate cyclase activity
- Lack at Mg-ATP complex
How quickly are the 3 hypos rectified after Mg supplementation?
Mg/PTH increases within MINUTES. PTH was there, just couldn't be secreted.

Ca takes longer since Active Vit D needs to be synthesized.
How is Mg involved in genes?
1. Involved in DNA replication
2. Involved in DNA repair
What types of DNA repair in Mg needed for/ describe Mg's role.
Two types of DNA repair:
1. NER - nucleotide excision repair (chucks out/replaced)
2. BER - base excision repair (single base removed/repaired)

Mg needed in a number of these steps.
Name the enzyme which is Mg-dependent in BER.
APE1: this protein is responsible for coordination of removal and transfer of damaged base to repair enzyme.
Besides the three hypos, what are some other deficiency signs of Mg?
Almost zero urinary excretion
• Neuromuscular signs: trousseau's compression of upper arm (arm spasms), muscle weakness, temors, headaches
• Naseua/ personality changes
• Anemia
What is the biochemical method of assesment for Mg?
Mg plasma concentration. If it's low, you are deficient, but if it's normal, you may/may not be deficienct.
When does Mg deficiency occur?
Anything that mucks up kidney
: decrease in renal absorption. Seen almost exclusively in hospital patients (because of other conditions)