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Occurrence of phosphodiesterase IV in the developing human brain, liver and placenta
Insights
Phosphodiesterase IV is present in human fetal tissues early in development. Enzyme activity changes with gestation, with specific characteristics identified in the brain, liver, and placenta.
Area of Science:
- Biochemistry
- Developmental Biology
- Enzymology
Background:
- Phosphodiesterase IV (PDE4) is a crucial enzyme involved in various cellular processes.
- Understanding PDE4 expression and activity during human fetal development is essential for comprehending tissue maturation.
Purpose of the Study:
- To investigate the presence, activity, and characteristics of phosphodiesterase IV in human fetal brain, liver, and placenta.
- To determine how PDE4 activity changes during intrauterine development.
Main Methods:
- Enzyme activity assays using bis-(p-nitrophenyl)-phosphate hydrolysis.
- Kinetic analysis (Km values) and inhibitor studies (EDTA, concanavalin A).
- Subcellular fractionation to determine enzyme localization.
Main Results:
- Phosphodiesterase IV was detected in human fetal brain, liver, and placenta from the 6th week of gestation.
- Enzyme activity peaked at 18-21 weeks and subsequently decreased.
- Kinetic parameters (Km) varied across tissues, and a sulfhydryl group was identified in the placental enzyme's active site.
- EDTA inhibited the enzyme in all tissues, while concanavalin A indicated no accessible carbohydrate moieties in the active site.
- Maximum activity was localized in soluble fractions of brain and liver, and a specific pellet fraction of the placenta.
Conclusions:
- Phosphodiesterase IV is present and dynamically regulated during human fetal development in key organs.
- The enzyme exhibits distinct kinetic and structural properties in the fetal brain, liver, and placenta.
- These findings provide insights into the role of PDE4 in human organogenesis and development.
Abstract:
The presence of phosphodiesterase IV has been demonstrated in the human fetal brain, liver and placenta as early as in the 6th week of intrauterine development. The enzyme activity in each tissue increases with gestation, being maximum at 18-21 wk and then decreases. The Km values of this enzyme for bis-(p-nitrophenyl)-phosphate hydrolysis in the brain, liver and placenta are 2.94 mM, 1.47 mM and 1.66 mM, respectively. Presence of sulfhydryl group in the active center of the placental enzyme has been demonstrated with the help of cationic study. EDTA inhibits the enzyme in all three tissues. Effect of concanavalin A reveals the absence or unexposition of glucose, mannose and N-acetylglucosamine moieties in the active site of the enzyme in each of the three tissues. Maximum enzyme activity has been found to be localized in the soluble supernatant fraction obtained on centrifuging the brain and liver homogenate at 105,000 x g and in 20,000 x g pellet of the placenta.