Biotinidase in human breast milk

Biotinidase activity in 19 samples of human breast milk was investigated with the sensitive high-performance liquid chromatography (HPLC)-fluorometric method that we developed. All samples exhibited biotinidase activity. For mature milk the mean activity of 17 samples was 0.208 nmol.min-1.mL-1 milk (range, 0.087-0.516 nmol.min-1.mL-1) and mean specific activity was 7.51 pmol.min-1.mg-1 protein (range, 2.17-17.2 pmol.min-1.mg-1). These values are relatively low compared with the activity in human serum (5.26 +/- 2.92 nmol.min-1.mL-1 serum and 95.6 +/- 53.1 pmol.min-1.mg-1 protein; n = 246). Biotinidase activities of milk obtained at various times after birth were not significantly different. However, biotinidase activity in colostrum was about five times higher than that of mature milk. The existence of biotinidase activity in all specimens suggests that this enzyme plays an important nutritional role during infancy.