IN-VITRO BIOSYNTHESIS OF LACTASE IN SUCKLING AND ADULT-RABBITS - REGULATORY MECHANISMS INVOLVED IN THE DECLINE OF THE LACTASE ACTIVITY

Steady state forms, levels and the in vitro biosynthesis of lactase-ph lorizin hydrolase (LPH) proteins have been studied in proximal and mid dle intestine of suckling and adult rabbits. In most adult tissues the lactase activity and the LPH protein content were low and the synthes is rate of the 200 kDa lactase precursor was reduced in comparison to suckling tissues. In a few tissues with low enzymatic activity the LPH protein content was relatively high, and high lactase synthesis occur red. In addition, the ratio (labeled lactase)/(lactase protein) was lo wer in the middle jejunum of the adult rabbit than in the proximal reg ion. Both decreased synthesis of LPH precursor and increased turnover or inactivation of the enzyme may cause the decline of the lactase act ivity.