Alpha-lactalbumin (LALBA) is the major protein found in breast milk. It is one of the reasons that human milk is superior to cow’s milk in feeding infants. It is found in the milk of many mammals, however. This protein helps to synthesize the milk sugar lactose. Alpha-lactalbumin is added to some infant formula mixtures to make them more nutritious.
Lactose is the major carbohydrate found in milk. It is a combination of the two sugars glucose and galactose. Alpha-lactalbumin acts as a regulatory unit for the enzyme that synthesizes lactose, by combining these two sugars. This protein complex stimulates lactose production and is itself stimulated by a hormone known as prolactin. When an infant sucks on a nipple, this stimulates prolactin production, which also causes the breast to fill with milk.
A major component of human breast milk is alpha-lactalbumin, which is itself a nutrient for the infant. The presence of it contributes to the nutritional benefits of breastfeeding. LALBA is known as a whey protein. Whey is a term often used in conjunction with cow’s milk. It indicates the soluble fraction of milk left over when cheese is made. Many bodybuilders take whey, from cows, as a supplement after workouts, so their bodies will use the protein fragments to increase muscle mass.
There are four main protein fractions in whey from cows, with the protein present in the greatest amounts being beta-lactoglobulin. This is not generally found in human breast milk. It can cause allergies in some children who are given cow’s milk. About one quarter of the whey protein is comprised of alpha-lactalbumin.
In contrast, alpha-lactalbumin makes up approximately 60% of the proteins in human whey protein. Additionally, breast milk has a much greater concentration of whey proteins than cow’s milk. Thus, the effective amount of LALBA is much greater in human milk.
Alpha-lactalbumin has high quantities of several types of amino acids that make it a particularly noteworthy protein to ingest. It has a large amount of tryptophan, which can induce sleep. This amino acid is converted, in the body, to the neurotransmitter serotonin, which can boost moods and lower stress levels. This is why a class of antidepressant drugs acts by increasing serotonin in people suffering from mood disorders.
Also present in this protein is a large quantity of the amino acid cysteine. This compound is thought to help boost the immune system. LALBA also contains branched-chain amino acids, which are essential for people. These types of amino acids are required by the body, but cannot be synthesized by it.
In humans, the gene for alpha-lactalbumin is known as the LALBA gene. The sequence of this gene shows a strong similarity to that of lysozyme. This is an antibacterial protein that is found in saliva and tears. Its evolution is thought to predate that for LALBA, which is also thought to have antibacterial properties.