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