Zinc (Zn2+)

Zinc absorption may involve formation of complexes with ______ (e.g. citric acid, histidine, other amino acids)

ligands

The Zn-binding protein ___________ is involved in the regulation by GI mucosal cells

metallothionein

Family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons, a reversible reaction that occurs relatively slowly in the absence of a catalyst. This enzyme, found primarily in erythrocytes and in renal tubule cells, is essential for acid-base balance/buffering and respiration. This enzyme has a very high affinity for zinc, which plays a catalytic role

Carbonic anhydrase

Enzymes secreted by the pancreas into the duodenum that are necessary for protein digestion. Zinc is bound tightly to this enzyme and is essential for enzymatic activity

Carboxypeptidase A

The loop of amino acids that protrudes from the zinc-binding site and is described as the Cys2/His2 finger

Zinc fingers

Enzyme needed for heme synthesis and is zinc dependent. This enzyme is made up of 8 subunits, each of which binds one zinc atom

Aminolevulinic acid dehydratase

Enzyme that is important in the NADH-dependent conversion of alcohols to aldehydes. Contains four zinc atoms per enzyme molecule, with two of the four required for catalytic activity and two required for structural purposes

Alcohol dehydrogenase

What are the biochemical indices of Zinc (4)?

-Blood levels of Zn -RBC levels of Zn -Zn content in hair -Reduced sperm count (males)

Which tissues/systems are affected by Zinc (5)?

-Growth -Sexual maturation -Reproduction -Skin -Immune system

Bioavailability of Zinc is dependent on which factors (3)?

-Physiological need (pregnancy & lactation) -Dietary factors (excess amounts of Ca, Fe, Cu, phytate and/or fiber, oxalic acid) -A factor in human milk that enhances zinc absorption by infants

What are the signs/symptoms of Zinc deficiency (9)?

-Poor appetite -Dermatitis/rash -Growth failure (in children, dwarfness) -Delayed sexual maturation -Mental lethargy (neuropsychological abnormalities) -Delayed wound healing -Impaired immunity -Impaired dark adaptation -Loss of taste sense

Why is bioavailability of Zn relatively high in meats, eggs, and seafood?

-Relative absence of compounds that inhibit zinc absorption -The presence of certain amino acids (cysteine and methionine)

What are the food sources of Zinc?

-Shellfish, beef, and other red meats -Nuts and legumes

How does Zinc affect immune function?

-Zinc is a structural component of thymic hormone -Zinc is a lymphocyte mitogen (causes expansion of immune cells) -Zinc regulates immune function

What are some of the metabolic roles of Zinc (7)?

1. Co-factor for a LARGE # of enzymes thereby influencing many metabolic pathways 2. Influences protein synthesis (e.g. DNA & RNA polymerase) (Zinc fingers) 3. Carbonic anhydrase (in RBC) 4. Alkaline phosphatase 5. Alcohol dehydrogenase (e.g. retinol--> retinal) 6. Carboxypeptidase A (from pancreas) 7. Aminolevulinic acid dehydratase (ALA dehydrase, heme synthesis)

What are the top 5 food sources for Zinc?

1. Oysters (43.4 mg/serving) 2. Beef (5.8 mg/serving) 3. Crab, Dungeness (4.6 mg/serving) 4. Turkey, dark meat (3.5 mg/serving) 5. Chicken, dark meat (2.4 mg/serving)

Zinc absorption ranges from ___-___%

30-50%

Recently, national dietary surveys in the US estimated that the average dietary Zinc intake was ____mg/day for adult women and ___mg/day for adult men

9 mg/day, 11 mg/day

Enzyme that contains four zinc atoms per enzyme molecule. Two of the four atoms are required for enzyme activity. and the other two are needed for structural purposes. Found mainly in bones and liver

Alkaline phosphatase

Which amino acid does metallothionein contain?

Cysteine; regulates copper

Why does Zn get lost through the pancreas?

Enteropancreatic cycle; Zn gets absorbed in the body, goes through the pancreas to help with digestion, then goes back to the small intestine

What are the zinc pancreatic functions?

Enzymes (Zn helps enzymes in pancreas)

Unabsorbed Zn, endogenous Zn (e.g. pancreatic secretions) and "mucosal" Zn is excreted via ______

Feces (main excretion route)

Zinc absorption is regulated by _______ cells

GI mucosal cells

The Zinc in whole grain products and plant proteins is ____ bioavailable due to their relatively high content of _______

LESS, phytic acid

Leavened whole grain breads (yeast) have ____ bioavailable zinc than unleavened whole grain bread

MORE

What is the DRI/RDA of Zinc for males and females?

Males: 11 mg/day Females: 8 mg/day

Zinc is relatively non-toxic, but may interfere with absorption and/or utilization of _____ and _____ and may reduce HDL cholesterol levels

copper and iron

Do we directly secrete minerals?

No

Zinc is primarily absorbed from where?

The upper portion of the SI (duodenum and upper jejunum)

_______ is the secondary Zn excretion route followed by _____ in small amounts

Urine, sweat

Why is zinc found in pancreatic juice?

Zn is involved with digestive enzymes; the enzymes need zinc to function

Zinc is absorbed via ________ absorption

active

Zinc leaving the liver binds mainly (about 70-75%) to ______, with the remaining zinc bound more tightly to ___________. Two Amino Acids (______ and ______) also loosely bind and transport less than 1% of zinc in the blood

albumin, a-2-macroglobulin, histidine and cysteine

Zinc passing into portal blood from the intestinal cell is mainly transported loosely bound to ______. Most zinc is then taken up by the ______, where the mineral is initially concentrated

albumin, liver