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Co-operativity in seminal ribonuclease function. Kinetic studies.
R Piccoli1, A Di Donato, G D'Alessio
1Dipartimento di Chimica Organica e Biologica, Università di Napoli, Italy.
The Biochemical Journal
|July 15, 1988
Summary
Bovine seminal ribonuclease (RNAse) exhibits non-hyperbolic kinetics due to mixed co-operativity, not enzyme heterogeneity or hysteresis. Subsite binding is essential for full enzyme activity, as supported by kinetic and binding studies.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Bovine seminal ribonuclease (RNAse) is an enzyme involved in RNA hydrolysis.
- Non-hyperbolic kinetics in enzymes can arise from various factors, including enzyme heterogeneity, hysteretic effects, or complex substrate interactions.
Purpose of the Study:
- To investigate the underlying causes of non-hyperbolic kinetics observed in bovine seminal RNAse.
- To elucidate the role of substrate binding and product effects in the enzyme's catalytic mechanism.
Main Methods:
- Kinetic studies using various substrates to analyze the rate-limiting hydrolytic reaction step.
- Analysis of substrate saturation curves and the effects of reaction products at different concentrations.
- Enzyme-subsite binding studies to correlate binding with enzyme activity.
Main Results:
- Non-hyperbolic kinetics were not attributed to enzyme microheterogeneity or hysteretic effects.
- Substrate saturation curves displayed an intermediate plateau.
- The reaction product exhibited both activating (low concentrations) and inhibiting (high concentrations) effects.
Conclusions:
- The observed kinetics are explained by mixed co-operativity, involving binding at specific subsites.
- Subsite binding is a prerequisite for the full catalytic activity of bovine seminal RNAse.
- A proposed model integrating kinetic and binding data supports these findings.