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Title:Proteolysis of mammary secretion proteins during involution of bovine mammary gland
Author(s):Aslam, Mueen
Doctoral Committee Chair(s):Hurley, Walter L.
Department / Program:Animal Sciences
Discipline:Animal Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Agriculture, Animal Culture and Nutrition
Chemistry, Biochemistry
Abstract:In cattle, during the early dry period the mammary gland undergoes a process of involution. The profile of mammary secretion proteins changes throughout the dry period. Increased proteolytic activity and breakdown fragments of milk proteins contribute to the composition of mammary secretions during dry period. The objectives of this study were (a) to determine the two-dimensional protein profile of mammary secretion proteins and peptides during involution, (b) to measure plasmin, plasminogen and plasminogen activator activity in mammary secretions collected during involution, and (c) to identify and characterize milk protein derived-peptides in mammary secretions during involution. Proteins in mammary gland secretions, collected from Holstein cows during the dry period, were analyzed by preparative isoelectric focusing, followed by SDS-PAGE. Protein profiles changed throughout the dry period. Intact casein bands were present throughout the dry period, but in reduced proportions from d 7 after drying-off through d 7 prepartum. Breakdown fragments of casein were particularly apparent in secretions from d 7 to 21 of the dry period. A fragment of $\beta$-CN ($\sim$13 kDa) was identified in secretions collected on d-1 prior to dry-off through d 21 of the dry period. Lactoferrin was found in all fractions after isoelectric focusing, but specific degradation products of lactoferrin were apparent only at certain times during the dry periods. Plasmin, plasminogen and plasminogen activator activities were significantly higher ($P <$ 0.05) on d 7, 14 and 21 of involution compared to d 7 postcalving. Immunoblot analysis showed that a number of peptides observed on d 7, 14 and 21 of involution were generated from $\alpha$s-casein, $\beta$-casein, $\kappa$-casein, or lactoferrin. Four peptides with apparent molecular weights ranging from 8 to 13 kDa were identified as $\beta$-casein fragments by amino acid sequence analysis. Mass spectrometric analysis of mammary secretions shows several peptides ranging from 0.8 to 12 kDa on d 7, 14, and 21 of involution. Mass spectrometric analysis of lactoferrin fractions collected from heparin-agarose chromatography showed at least four peaks of about 16, 20, 56, and 63 kDa. Results from this study show that $\beta$-casein-derived peptides are produced by the plasmin cleavage. These and other peptides generated in mammary secretions may have functional role in the involuting mammary gland.
Issue Date:1996
Rights Information:Copyright 1996 Aslam, Mueen
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9712193
OCLC Identifier:(UMI)AAI9712193

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