The activity of γ-glutamyltransferase was measured in a series of human breast milk samples collected during the first post natal week. All the samples showed considerable γ-glutamyltransferase activity. The mean level fell from 28.8 U/ml to 3.9 U/ml seven days later. There was a highly significant correlation between γ-glutamyltransferase and the protein content of the samples studied.
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