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Interaction between actomyosin and 8-substituted ATP analogs
Abstract:
Various 8-substituted ATP analogs were synthesized, and their reactions with myosin and actomyosin were studied. The nucleoside triphosphates (NTPs) with an amino group at the 6 position and hydrogen at the 8 position, and formycin 5'-triphosphate (FTP) were hydrolyzed by myosin very slowly in the presence of Mg2+ and rapidly in the presence of EDTA and K+. In contrast, NTPs with substitution of the 8 position, other than FTP, were readily hydrolyzed by myosin in the presence of Mg2+ but were hardly hydolyzed in the presence of EDTA and K+. The Michaelis constant (Km) for hydrolysis of 8-substituted NTP by heavy meromyosin was much larger than the dissociation constant (Kfl) for binding of heavy meromyosin with NTP estimated from the change in tryptophan fluorescence. All the NTPs with no substitution at the 8 position, and FTP, caused an initial Pi burst, actin activation of myosin NTPase, superprecipitation of actomyosin, and myofibrillar contraction. On the other hand, all the 8-substituted NTPs in three possible conformations did not cause these phenomena, regardless of the conformation. These results were discussed in relation to the hindrance of rotation about the glycosidic bond accompanying an 8 substitution.
Insights
Researchers studied ATP analogs and their interaction with myosin. Results show 8-substituted ATP analogs hinder muscle contraction, unlike unsubstituted ATP, impacting myosin
Area of Science:
- Biochemistry
- Molecular Biology
- Muscle Physiology
Background:
- Adenosine triphosphate (ATP) is the primary energy currency for muscle contraction.
- Myosin ATPase is the enzyme responsible for ATP hydrolysis during muscle activity.
- Understanding ATP analog interactions provides insights into enzymatic mechanisms.
Purpose of the Study:
- To synthesize and investigate the biochemical properties of various 8-substituted ATP analogs.
- To determine the effects of these analogs on myosin and actomyosin function.
- To elucidate the role of the 8-position substitution in ATP hydrolysis and muscle contraction.
Main Methods:
- Chemical synthesis of 8-substituted ATP analogs.
- Enzymatic assays measuring ATP hydrolysis rates by myosin and heavy meromyosin.
- Analysis of binding kinetics using tryptophan fluorescence.
- Assessment of actomyosin superprecipitation and myofibrillar contraction.
Main Results:
- Unsubstituted ATP analogs and formycin 5'-triphosphate (FTP) were slowly hydrolyzed by myosin with Mg2+ but rapidly with EDTA/K+.
- 8-substituted ATP analogs (excluding FTP) were readily hydrolyzed by myosin with Mg2+ but poorly with EDTA/K+.
- 8-substituted ATP analogs failed to induce Pi burst, actin activation, superprecipitation, or contraction, irrespective of conformation.
Conclusions:
- Substitution at the 8-position of ATP significantly impairs myosin's ability to catalyze muscle contraction.
- Hindrance of glycosidic bond rotation due to 8-substitution is a key factor in the observed inhibitory effects.
- These findings highlight the structural requirements for ATP analogs to function effectively in the muscle contractile machinery.