Related Experiment Video
Updated: Aug 7, 2026

Fluorescence-based Monitoring of PAD4 Activity via a Pro-fluorescence Substrate Analog
Published on: November 5, 2014
Effect of polyamines on the carbamoyl-phosphate synthase activity of CAD protein
1Department of Biochemistry, University Medical School of Debrecen, Hungary.
Abstract:
The effects of polyamines were studied on carbamoyl-phosphate synthase II (EC 6.3.5.5.) which is the first and rate limiting enzyme in mammalian pyrimidine synthesis. Polyamines in physiological concentrations (0.1-1 mM) strongly inhibited the carbamoyl-phosphate synthesis. Of the polyamines tested spermine was the most effective followed by spermidine and putrescine. Spermine increased the KM for ATP and the requirement for Mg++ of carbamoyl-phosphate synthase reaction. UTP, an inhibitor, had similar, while phosphoribosyl-pyrophosphate, an activator of the enzyme had an opposite effect. Increasing concentrations of phosphoribosyl-pyrophosphate completely reversed the inhibition caused by spermine, while did not influence the degree of inhibition caused by UTP. A possible physiological role of polyamines in synchronizing the substrate and activator functions of phosphoribosyl-pyrophosphate in pyrimidine synthesis is suggested.
Related Concept Videos
Phosphorylation
During phosphorylation, protein kinases transfer the terminal phosphate group of ATP to specific amino acid side chains of substrate proteins. Serine, threonine, and tyrosine are the most commonly...
Covalently Linked Protein Regulators
These groups modify specific amino acids in a protein.
Cell Specific Gene Expression
Allosteric Proteins-ATCase
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
cAMP-dependent Protein Kinase Pathways
Calmodulin-dependent Signaling
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...

