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[Different cooperativity of some oxidoreductases to specialized and nonspecialized regulators]
Abstract:
The activation of 2 different mouse liver enzymes: cytozolic disulfide reductase (DSR) and mitochondrial NAD-isocitrate dehydrogenase (ICDH), by catecholamines and especially by 3',5'-AMP is characterized by negative cooperativity; substrate (both enzymes), protamine and EDTA (DSR) produce the positive cooperativity type of activation; DSR activation by isopropyl noradrenaline and serotonine is characterized by hyperbolic kinetics. Consequently, one and the same enzyme can combine positive cooperativity to non-specialized regulators (substrate, protamine, EDTA) with negative cooperativity to specialized regulators (3',5'-AMP, catecholamines). The systems, switching on by catecholamines and 3',5'-AMP, are oligomeric, and the degree and even the type of cooperativity can modify depending on the kind of catecholamine. The negative cooperativity is revealed in literature for many effects of catecholamines and 3',5'-AMP. Probably, it guarantees the broad range of regulations. Dose effect curves for 3',5'-AMP, catecholamines and other hormones should be analyzed on the basis of allosteric protein kinetics. A simple nomogram is given to estimate nH less than 1.
Insights
Mouse liver enzymes like disulfide reductase (DSR) and NAD-isocitrate dehydrogenase (ICDH) show complex activation. Regulators like catecholamines and cyclic AMP (cAMP) induce negative cooperativity, while substrates induce positive cooperativity.
Area of Science:
- Biochemistry
- Enzyme kinetics
- Molecular biology
Context:
- Investigates the regulatory mechanisms of key mouse liver enzymes.
- Focuses on the distinct activation patterns of disulfide reductase (DSR) and NAD-isocitrate dehydrogenase (ICDH).
- Examines the role of catecholamines and cyclic AMP (cAMP) in enzyme regulation.
Purpose:
- To characterize the cooperativity types in enzyme activation by various effectors.
- To understand how different regulators modulate enzyme activity through positive and negative cooperativity.
- To explore the oligomeric nature of enzyme systems regulated by catecholamines and cAMP.
Summary:
- Mouse liver enzymes DSR and ICDH exhibit negative cooperativity when activated by catecholamines and cAMP.
- Substrates, protamine, and EDTA induce positive cooperativity in DSR activation.
- Enzyme systems regulated by catecholamines and cAMP are oligomeric, with cooperativity type varying by catecholamine.
- Negative cooperativity likely ensures a broad regulatory range for these signaling pathways.
Impact:
- Highlights the complex, context-dependent nature of enzyme regulation.
- Suggests allosteric protein kinetics should be used to analyze dose-effect curves for hormones.
- Provides a nomogram for estimating Hill coefficients (nH) less than 1, aiding kinetic analysis.