MODEL OF MILK PROTEIN-SYNTHESIS - A MECHANISTIC MODEL OF MILK PROTEIN-SYNTHESIS IN THE LACTATING BOVINE MAMMARY-GLAND

A model of amino acid (AA) uptake and metabolism by the mammary gland (udder) of a high-producing dairy cow in mid-lactation is presented. T wo cell types, milk-secreting alveolar epithelial cells, and constitut ive stromal cells are represented separately. Solution of the model at steady state, with appropriate assumptions, allows calculation of ami no acid (AA) pool sizes in tissue bound AA and mirk protein bound AA, and concentrations of intracellular free AA. Bidirectional flux rates of amino acids between each of these pools is also estimated. The flow of two amino acids, phenylalanine (Phe) and tyrosine (Tyr), is descri bed using uptake kinetics of the L-system AA transporter. Model result s suggest that AA uptake capacity of the alveolar cells, and the amoun t/activity of protein translation components limit the rate of milk pr otein synthesis in the high-producing dairy cow. A considerable amount of experimental work is necessary to provide data, if a comprehensive quantitative understanding of milk protein synthesis is to be achieve d. (C) 1997 Academic Press Limited.