N-acetyl- β-hexosaminidase activity in human breast milk

1. 1. The lysosomal enzyme, N-acetyl- β-hexosaminidase (HEX) is present in human breast milk. It is composed predominantly of “A” (heat-labile) and “B” (heat-stable) isozymes which coelute with the corresponding major serum isozymes on DE-52 ion-exchange chromatography. 2. 2. Total HEX activity in “early” milk obtained at 2.8 ± 1.4 weeks post partum, is approx. 2.5-fold higher (87 ± 29 nmol/60'/mg protein, n = 10) than that of pregnancy serum (35.7 nmol/60'/mg protein) prior to delivery. 3. 3. These levels increase to greater than 3-fold (110 ± 20 nmol/60'/ mg protein, n = 13) as the milk matures (10.3 ± 4.2 weeks). 4. 4. The specific activity of HEX A in the milk changes little with time post partum, because absolute levels are decreasing simultaneous with decreases in milk protein. 5. 5. In contrast, HEX B specific activity is increased, as absolute levels (per volume) remain constant in the face of decreasing milk protein content. 6. 6. These changes result in a high degree of correlation ( r = 0.81) between time of lactation and % HEX A observed.