TY - JOUR
T1 - Selective Proteolysis of α-Lactalbumin by Endogenous Enzymes of Human Milk at Acidic pH
AU - Gan, Junai
AU - Zheng, Jingyuan
AU - Krishnakumar, Nithya
AU - Goonatilleke, Elisha
AU - Lebrilla, Carlito B.
AU - Barile, Daniela
AU - German, J. Bruce
PY - 2019/1/1
Y1 - 2019/1/1
N2 - Scope: The use of human milk products is increasing for high-risk infants. Human milk contains endogenous enzymes that comprise a dynamic proteolytic system, yet biological properties of these enzymes and their activities in response to variations including pH within infants are unclear. Human milk has a neutral pH around 7, while infant gastric pH varies from 2 to 6 depending on individual conditions. This study is designed to determine the specificity of enzyme–substrate interactions in human milk as a function of pH. Methods and results: Endogenous proteolysis is characterized by incubating freshly expressed human milk at physiologically relevant pH ranging from 2 to 7 without the addition of exogenous enzymes. Results show that the effects of pH on endogenous proteolysis in human milk are protein-specific. Further, specific interactions between cathepsin D and α-lactalbumin are confirmed. The endogenous enzyme cathepsin D in human milk cleaves α-lactalbumin as the milk pH shifts from 7 to 3. Conclusions: This study documents that selective proteolysis activated by pH shift is a mechanism for dynamic interactions between human milk and the infant. Controlled proteolysis can guide the use of human milk products based on individual circumstance.
AB - Scope: The use of human milk products is increasing for high-risk infants. Human milk contains endogenous enzymes that comprise a dynamic proteolytic system, yet biological properties of these enzymes and their activities in response to variations including pH within infants are unclear. Human milk has a neutral pH around 7, while infant gastric pH varies from 2 to 6 depending on individual conditions. This study is designed to determine the specificity of enzyme–substrate interactions in human milk as a function of pH. Methods and results: Endogenous proteolysis is characterized by incubating freshly expressed human milk at physiologically relevant pH ranging from 2 to 7 without the addition of exogenous enzymes. Results show that the effects of pH on endogenous proteolysis in human milk are protein-specific. Further, specific interactions between cathepsin D and α-lactalbumin are confirmed. The endogenous enzyme cathepsin D in human milk cleaves α-lactalbumin as the milk pH shifts from 7 to 3. Conclusions: This study documents that selective proteolysis activated by pH shift is a mechanism for dynamic interactions between human milk and the infant. Controlled proteolysis can guide the use of human milk products based on individual circumstance.
KW - bioactivity
KW - human milk
KW - pH
KW - protein
KW - selective proteolysis
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U2 - 10.1002/mnfr.201900259
DO - 10.1002/mnfr.201900259
M3 - Article
C2 - 31271254
AN - SCOPUS:85069685323
JO - Molecular Nutrition and Food Research
JF - Molecular Nutrition and Food Research
SN - 1613-4125
M1 - 1900259
ER -