Casomorphin

Casomorphins are peptides, i.e protein fragments, derived from the digestion of milk protein. The distinguishing characteristics of casomorphins are that they have opioid effects.

The most important casomorphins from bovine milk are those released from the digestion of β-casein into β-casomorphins, sometimes denoted as BCM followed by a numeral indicating the number of amino acids in the sequence. Notably, BCM7 has been implicated in a number of medical conditions, including diabetes, heart disease, and symptoms of autism and schizophrenia. However, it appears that only some individuals are susceptible.

In cattle, the amount of β-casein, and hence the potential release of β-casomorphins, varies between species and breeds. Typically, beta-casein comprises about one third of the casein in milk, or about 12 grams per litre of milk. However, there are at least 13 different variants of the β-casein protein in cattle population, with any one cow producing milk that will contain either one or two of these 13 variants.

Each variant fits into one of two main categories known as A1 and A2. In cattle, A1-type β-caseins have the amino acid histidine at position 67 whereas the A2-type β-caseins have the amino acid proline at position 67. Laboratory experiments show that the casomorphin known as BCM7 is only released from the A1-type β-caseins. The potential release of BCM7 is about 0.4 grams per litre of milk (assuming as above that there are 12g of β-casein per litre).

Human digestion may break down casomorphins into inactive dipeptides by the enzyme dipeptidyl peptidase-4. This enzyme is found in the digestive tract and in some endocrine cells.

There is also the potential for release of casomorphins from human milk. However, human BCM7 (Tyr-Pro-Phe-Val-Glu-Pro-Ile) differs from the bovine form (Tyr-Pro-Phe-Pro-Gly-Pro-Ile) at two amino acid positions.

Scientific understanding of the biochemistry and pharmacology of casomorphins is incomplete. A recent scientific review is provided by Kaminski et al (2007).

Health

Casein has been documented to break down in the stomach to produce the peptide casomorphin, an opioid that acts as a histamine releaser.

Diets that eliminate foods containing casein are promoted at conferences for parents of children with ASD, and some books, web sites, and discussion groups contain testimonials describing benefits in autism-related symptoms, notably social engagement and verbal skills. Studies supporting these claims have had significant flaws, so the data are inadequate to guide treatment recommendations.

Some known casomorphins

β-Casomorphin 1-3

• Structure: H-Tyr-Pro-Phe-OH
• Chemical formula: C₂₃H₂₇N₃O₅
• Molecular weight: 425.48 g/mol

Bovine β-casomorphin 1-4

• Structure: H-Tyr-Pro-Phe-Pro-OH
• Chemical formula:
• Molecular weight: 522.61 g/mol

Bovine β-casomorphin 1-4, amide

• Structure: H-Tyr-Pro-Phe-Pro-NH₂
• Chemical formula: C₂₈H₃₉N₅O₇
• Molecular weight: 557.64 g/mol

Bovine β-casomorphin 5

• Structure: H-Tyr-Pro-Phe-Pro-Gly-OH
• Chemical formula: C₃₀H₃₇N₅O₇
• Molecular weight: 594.66 g/mol

Bovine β-casomorphin 7

• Structure: H-Tyr-Pro-Phe-Pro-Gly-Pro-Ile-OH
• Chemical formula: C₄₁H₅₅N₇O₉
• Molecular weight: 789.9 g/mol

Bovine β-casomorphin 8

• Structure: H-Tyr-Pro-Phe-Pro-Gly-Pro-Ile-Pro-OH
• Chemical formula: C₄₆H₆₂N₈O₁₀
• Molecular weight: 887.00 g/mol

(Note there is also a form of bovine β-Casomorphin 8 that has Histideine instead of Proline in position 8, with this depending on whether it is derived from A1 or A2 beta-casein)

References