Retinyl palmitate hydrolase activity in human liver

Retinyl palmitate hydrolase (RPH) activity was studied in human liver after the optimal conditions of the assay in normal human liver homogenates were determined. The mean activity was 118 ± 66 nmol · min−1 · g−1 (x̄ ± SD) protein in liver homogenates from six children and seven adults; no correlation was found between liver hydrolase activity and the enzyme endogenous substrate, ie, liver vitamin A concentrations. RPH activity was also studied in a human model of vitamin A deficiency represented by 22 children with biliary atresia: 11 patients with vitamin A deficiency (liver vitamin A concentration < 70 nmol/g wet wt of liver) and 11 patients with normal vitamin A status after vitamin A treatment. The enzymatic assay had to be conducted after the removal of endogenous bile salts by cholestyramine because bile salts are accumulated in the liver of children with biliary atresia. No correlation was found between RPH activity and vitamin A status.