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Updated: Aug 5, 2026
Measuring Lactase Enzymatic Activity in the Teaching Lab
Published on: August 6, 2018
Mechanism of maturational decline of rat intestinal lactase-phlorizin hydrolase
K K Tsuboi1, L K Kwong, P Sunshine
1Department of Pediatrics, Stanford University School of Medicine, CA 94305-5119.
Insights
The maturational decline of lactase-phlorizin hydrolase (LPH) is due to increased turnover, not reduced synthesis. Other digestive enzymes like sucrase-isomaltase (SI) and maltase-glucoamylase (MG) increase due to accelerated synthesis.
Area of Science:
- Biochemistry
- Molecular Biology
- Gastroenterology
Background:
- Lactase-phlorizin hydrolase (LPH) activity declines during maturation in young rats.
- Associated increases in sucrase-isomaltase (SI) and maltase-glucoamylase (MG) activities are observed.
- Cellular concentrations of these enzymes change in parallel with their activities.
Purpose of the Study:
- To investigate the mechanisms behind the maturational decline of LPH activity.
- To compare LPH regulation with that of SI and MG during maturation.
- To elucidate the roles of synthesis and turnover in enzyme concentration changes.
Main Methods:
- Studied enzyme activities and cellular concentrations in rats from suckling to post-weaned stages.
- Utilized labelled leucine to examine enzyme synthesis rates.
- Assessed enzyme turnover using fractional synthesis rates and leucine disappearance from prelabelled pools.
Main Results:
- LPH synthesis remained constant despite declining concentration.
- SI and MG concentrations increased due to accelerated synthesis.
- LPH turnover rate increased, mirroring the decline in its concentration.
Conclusions:
- The maturational decline of LPH is primarily caused by accelerated enzyme turnover.
- Synthesis rates of SI and MG increase to support their rising concentrations.
- These findings support the hypothesis that LPH decline is turnover-driven.
Abstract:
The maturational decline in lactase-phlorizin hydrolase (LPH) activity was studied in groups of young rats ranging from suckling to early post-weaned states. Associated maturational increases in sucrase-isomaltase (SI) and maltase-glucoamylase (MG) activities were also examined as a comparison. Over this time period changes in cellular concentrations of the three enzymes were observed, reflecting corresponding changes in enzyme activities. Synthesis patterns accompanying these maturational changes in concentration were examined using labelled leucine as a marker. Synthesis of LPH was found to be maintained at constant rates independent of the maturation-associated decline in its concentration, whereas the increases in cellular concentrations of SI and MG were due to accelerated synthesis of the enzyme. Turnover of LPH, based on both the fractional synthesis rate and the disappearance rate of labelled leucine from prelabelled LPH pools, was increased in a quantitatively similar way to the decline in LPH concentration. These findings are consistent with our earlier proposal that the maturational decline of LPH occurs because of accelerated turnover, without a decrease in its rate of synthesis.
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