Article ID Journal Published Year Pages File Type
2435903 International Dairy Journal 2006 8 Pages PDF
Abstract

Samples of prepartum secretion, colostrum and mature milk were analysed for variation in activity of cathepsin D and cysteine protease due to lactation stage and somatic cell count (SCC). In spite of considerable variation between animals, cathepsin D activity was found to be highest in prepartum secretion, lowest in colostrum and at intermediate levels in milk throughout lactation. Levels of cysteine protease activities were highest 1 week postpartum and lowest in early/mid-lactation milk. The activity of an unidentified milk protease with specificity different from cathepsin D and cysteine proteases was also detected in milk, but had very low activity in prepartum secretions and colostrum. By immunoblotting, prepartum secretion was found to contain both cathepsin D and procathepsin D, while only procathepsin D could be detected in colostrum and milk. Cathepsin D activity was positively correlated with SCC, and immunoblotting indicated that the elevated activity derived from cathepsin D was due to increased level of immunoreactive procathepsin D in high SCC milk, and not to increased levels of mature cathepsin D. This indicates that activation of procathepsin D does not occur at elevated SCC.

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Life Sciences Agricultural and Biological Sciences Food Science
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