The kinetics of interactions between the peptides calcitonin or neurotensin, and synaptosomal membrane Na+, K+-ATPase activity was characterized in this study. Calcitonin is a 32-amino acid peptide produced by the thyroid gland, whose main role is to prevent bone resorption. Calcitonin produced a non-competitive type of inhibition at varied potassium concentrations whereas in the presence of sodium and ATP, calcitonin produced an uncompetitive and competitive type of inhibition, respectively. Neurotensin is a basic tridecapeptide which also inhibits Na+, K+-ATPase activity. Therefore, in the presence of higher sodium concentrations the peptide produced a competitive interaction and it produced a non-competitive type of inhibition at varied potassium and ATP concentrations. In summary, calcitonin and neutotensin behave as enzyme inhibitors but, each one leads to a characteristic type of enzyme inhibition at varied substrate concentrations due to differences in peptide structure and functionality that could be influencing the kinetics of substrate interactions.
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