Secretion of whey acidic protein and cystatin is down regulated at mid-lactation in the red kangaroo (Macropus rufus)

Milk collected from the red kangaroo (Macropus rufus) between day 100 and 2 60 of lactation showed major changes in milk composition at around day 200 of lactation, the rime at which the pouch young begins to temporarily exit the pouch and eat herbage. The carbohydrate content of milk declined abrupt ly at this time and although there was only a small increase in total prote in content, SDS PACE analysis of milk revealed asynchrony in the secretory pattern of individual proteins. The levels of alpha -lactalbumin, beta -lac toglobulin, serum albumin and transferrin remain unchanged during lactation . In contrast, the protease inhibitor cystatin, and the putative protease i nhibitor whey acidic protein (WAP) first appeared in milk at elevated conce ntrations after approximately 150 days of lactation and then ceased to be s ecreted at approximately 200 days. In addition, a major whey protein, late lactation protein, was first detected in milk around the time whey acidic p rotein and cystatin cease to be secreted and was present at least until day 260 of lactation. The co-ordinated, but asynchronous secretion of putative protease inhibitors in milk may have several roles during lactation includ ing tissue remodelling in the mammary gland and protecting specific protein s in milk required ia; physiological development of the dependent young. (C ) 2001 Elsevier Science Inc. All rights reserved.