Transcript Lac

Milk Protein, Colostrum, Lactose,
Minerals and MUN
Milk Proteins (Caseins)
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Found in milk in the form of a Micelle (a dense protein granule). The phosphate groups
covalently bound to the casein molecules are involved in binding Calcium (Ca) via ionic bonds.
After caseins are phosphorylated, Ca++ binds to the phosphate to initiate polymerization of
the micelle particles. This [casein-PO4- Ca++ - PO4-casein] structure is key to micelle
formation.
The casein micelle functions as a source of nutrients for the neonate: supplying amino acids,
calcium and phosphate.
Micelles are ~140 nanometers in diameter. They are composed of alpha- , beta-, and kappacaseins. a-Caseins are in multiphosphorylated forms. ß-Casein is a major casein in cow milk,
but is the minor casein in human milk. k-Casein (a glycoprotein) is distributed throughout the
casein micelle and acts to stabilize the micelle. Gamma-caseins (part of the proteose peptone
fraction of milk) are C-terminal fragments of ß-casein, which are released by plasmin
digestion, mostly while the milk is in the gland.
The destabilization of the casein micelle structure and partial hydrolysis of casein decreases
the quality of fluid milk and the yield of cheese from milk. Conversely, the destabilization of
the casein micelle by proteases is part of the mechanism involved in milk digestion in the
stomach and intestine. Controlled hydrolysis of casein is also the means of producing cheeses
and other cultured milk products.
Milk Proteins
Casein Micelle Structure
Mouse Casein Micelles
Milk Proteins (Major Cow Whey
Proteins)
• ß-LACTOGLOBULIN (ß-LG): Is ~50 % of the total whey protein content in
milk. Is the major whey protein in ruminants and pigs. It is not found in
milk of many species. The function of ß-LG is unknown; it may be a fatty
acid or lipid binding protein. It does have sequence similarities with
retinol-binding proteins, but this may not be its function. Generally it is
found in milk of species which transport high levels of immunoglobulins
during colostrum formation, however the specific relationship between
the presence of ß-LG and immunoglobulin transport remains unclear.
• a-LACTALBUMIN (a-LA): Is ~25 % of the total whey protein content in milk.
Is the "B" protein of the Lactose Synthase enzyme complex . Therefore, it
is of major interest in terms of the control of milk secretion. May have
other nonspecific effects on the integrity of milk fat membranes. a-LA
binds Ca and Zn.
Milk Proteins (Minor Cow Whey
Proteins)
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SERUM ALBUMIN (SA) : Serum albumin comes from the serum; it is not
synthesized in the mammary gland. It is presumed to enter the milk via "leakage"
by the paracellular pathway, or by uptake with other components such as
immunoglobulins. There does not seem to be a more specific mechanism of
transport. Increases in milk concentration of serum albumin occur especially
during mastitis and during mammary involution. Function of serum albumin in
milk is unknown. It does bind to fatty acids, as well as other small molecules.
IMMUNOGLOBULINS (Ig): include IgG1, IgG2, IgA, IgM : Immunoglobulins are in
very high concentrations in colostrum, but much lower concentrations in milk.
Immunoglobulins are part of the passive immunity transported to the neonate via
colostrum in many species. They are part of the mammary immune system.
Secretory Component (SC) is the part of the IgA receptor which hydrolysed by a
protease and remains attached to IgA as it is secreted from the cell.
Milk Proteins (Minor Cow Whey
Proteins)
• Lactoferrin (LF) - Is an iron binding protein and has antibacterial
properties. Relatively low concentrations during lactation in cow milk, but
is increased during mastitis and involution. Lactoferrin may also be an
immunomodulator. Lactoferrin is in human milk in high concentrations; in
fact it is the major whey protein in human milk. Lactoferrin is the major
nonspecific disease resistance factor found in the mammary gland.
• Lactoperoxidase - Is an enzyme that breaks down hydrogen peroxide. It
has antibacterial properties.
• Lysozyme - Is an enzyme that cleaves the carbohydrate polymers of the
bacterial cell wall. High activity in human milk and possibly in horse milk,
but very low activity in cow milk.
Cow Milk Protein Variants
Colostrum
Milk Composition in Early
Lactation
Concentrations of Antibodies
Antibody Structure
Antigen
CH1
CH2
CH3
Antibody IgG1, 2, 3, 4, IgM, IgA Heavy Chains
Antibody Kappa, Lambda Light Chains
Antibody Structure
IgG Antibody Structure
IgA and IgM Antibody Structure
Feeding Colostrum
Pooling Colostrum
Colostrum Quality
Colostrum Quality on Calf Survival
Saving Colostrum
Lactose Production
Lactose Biosynthesis
Sources of Glucose
Utilization of Glucose in the
Bovine Mammary Gland
Metabolic Regulation of Lactose
Production
Alpha-lactabumin
 A major whey protein in bovine, porcine
and human milk.
 ~ 1.2 g/L in bovine milk and 1.5 g/L in porcine milk
 Important source of dietary amino acids for calves, piglets and
infants
Contains a higher percentage of the essential amino acids
(Threonine, Methionine, Lysine, Valine, Leucine, Isoleucine, Histidine,
Phenylalanine, Tryptophan, Alanine) than the other major milk
proteins
 Combines with ß1,4 galactosyltransferase within mammary epithelial cells
to form “lactose synthase”.
 Lactose is the primary osmole in milk, which, in turn, regulates milk
volume.
The most tightly controlled milk protein gene to lactation
Alpha-lactalbumin Production
During Pregnancy
Alpha-Lactalbumin Levels in
Serum at Calving
Beta 1,4 Galactosyltranferase
 A enzyme found in the golgi apparatus of all cells.
 Normally involved in glycosylation of proteins
 Combines with alpha-lactalbumin within the mammary epithelial cells to
form “lactose synthase”.
 Alpha-lactalbumin modifies Beta 1,4 Galactosyltransferse’s normal
function causing it to hook glucose and galactose together to form lactose
Lactose Synthesis
Mammary Epithelial Cell Cartoon
Alpha-lactalbumin Knock-out Mice
Phenotype of Alpha-lactalbumin
Knock-out Mice
Phenotype of Beta 1,4
Galactosyltransferase Knock-out Mice
Production of Bovine Alphalactalbumin in Transgenic Sows
Lactose Production in Alphalactalbumin Transgenic Sows
%
(g/dL)
Control
6
5.5
(n=10)
Transgenic
5
(n=8)
4.5
4
3.5
3
2.5
2
Mean ± SEM
*
* p < 0.05
*
**
0 2 4 6 8 10 12 14 16 18 20
Day of Lactation
Milk Protein % in Alpha-lactalbumin
Transgenic Pigs
Milk Production in Alphalactalbumin Transgenic Sows
8
Milk Yield
7
(kg/d)
6
5
4
3
2
1
0
Control
(n=10)
*
*
Transgenic
(n=8)
*
Mean ± SEM
* p<0.05
3
6
9
Day of Lactation
12
Growth of Piglets Nursed by Alphalactalbumin Transgenic Sows
Cumulative Weight Gain
kg
4
3.5
3
2.5
2
1.5
1
0.5
0
Mean Weight (kg)
*
Control
TG
(n=200) (n=200)
* d 7-21
*
d0
1.46 ±
0.03
1.42 ±
0.02
d 20
4.48 ±
0.07
4.91 ±
0.05 *
Control
Transgenic
2 4 6 8 10 12 14 16 18 20
Day of Lactation
Mean ± SEM * p<0.05
Weight Gain by Piglets Nursed by
Alpha-lactalbumin Transgenic Sows
Mean Rate of Piglet Gain Throughout Lactation
mean rate of gain (kg/d)
0.25
*
0.2
0.15
0.1
0.05
0
control
transgenic
Ion Movement into Milk
Transfer of Calcium and Phosphorus
into Milk
Altered Lactose and Ion Content in
Milk
Milk Urea Nitrogen (MUN)
Using MUN
Individual and Daily MUN Samples
High MUN Values
Low MUN