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Human milk ribonuclease
Abstract:
Two components having ribonuclease (EC 3.1.27.5) activity were isolated from human milk. Each component of human milk ribonuclease (RNAase) moved at a slightly different rate when electrophoresed on polyacrylamide gel but at the same rate when ultracentrifuged. The major component had a molecular weight of approx. 14 000, an isoelectric point of pH 7.9, and exhibited a broad absorbance maximum between 277 and 281 nm. Human milk RNAase hydrolyzed yeast RNA, poly(cytidylic acid) and poly(uridylic acid) but not DNA, poly(adenylic acid) or poly(guanylic acid). Maximum activity occurred at pH 7.7 and 60 degrees C. Amino acid analysis of the major component revealed a large number of alanine, valine, glycine and aspartic acids but no tryptophan or free sulfhydryl groups. Lysine was the N-terminal amino acid. Tryptic hydrolysis yielded 18 peptides, some of which are similar to those from bovine pancreatic RNAase. Human milk RNAase activity was increased in the presence of NaCl, KCl and sodium citrate and decreased by CaCl(2), MgCl(2), FeSO(4), ZnSO(4) and CuSO(4).
Insights
Two ribonuclease (RNAase) components were isolated from human milk. These enzymes effectively degrade RNA, with optimal activity at pH 7.7 and 60°C, and show similarities to bovine pancreatic RNAase.
Area of Science:
- Biochemistry
- Enzymology
- Human Milk Composition
Background:
- Human milk contains various bioactive components.
- Ribonucleases (RNAases) are enzymes that degrade RNA.
- Understanding milk enzymes is crucial for infant nutrition and health.
Purpose of the Study:
- To isolate and characterize ribonuclease (RNAase) components from human milk.
- To determine the enzymatic properties and substrate specificity of human milk RNAase.
- To compare human milk RNAase with other known RNAases.
Main Methods:
- Isolation of two RNAase components using polyacrylamide gel electrophoresis and ultracentrifugation.
- Characterization of the major component's molecular weight, isoelectric point, and absorbance spectrum.
- Enzymatic assays to determine substrate specificity, optimal pH, and temperature.
- Amino acid analysis and tryptic hydrolysis for structural comparison.
Main Results:
- Two distinct human milk RNAase components were identified.
- The major component has a molecular weight of ~14,000 Da, pI of 7.9, and hydrolyzes yeast RNA, poly(C), and poly(U).
- Optimal activity is at pH 7.7 and 60°C; activity is modulated by various salts and divalent cations.
Conclusions:
- Human milk contains active ribonuclease enzymes with specific substrate preferences.
- The characterized human milk RNAase shares some structural similarities with bovine pancreatic RNAase.
- These findings contribute to the understanding of enzymatic activities in human milk.