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Purine nucleotide pyrophosphotransferase from Streptomyces morookaensis, capable of synthesizing pppApp and pppGpp
Abstract:
Purine nucleotide pyrophosphotransferase was purified to apparent homogeneity from a culture filtrate of Streptomyces morookaensis. It is a monomeric protein with a molecular weight of 24 000-25 000, and its isoelectric point is 6.9. The enzyme synthesizes purine nucleoside 5'-phosphate (mono, di, or tri) 3'-diphosphates such as pppApp, ppApp, pApp, pppGpp, ppGpp and pppIpp by transferring a pyrophosphoryl group from the 5'-position of ATP, dATP and ppApp to the 3'-position of purine nucleotides. The purified enzyme catalysed the formation of 435 mumol of pppApp and 620 mumol of pppGpp from ATP and GTP per min mg protein under the standard conditions. The enzyme requires absolutely a divalent cation for activity, and optimum pH for the enzyme activity lay above 10 for Mg2+, for Co2+ and Zn2+ from 9 to 9.5, and for Fe2+ from 7.5 to 8. The following Michaelis constants were determined: AMP, 2.78 mM; ADP, 3.23 mM; GMP, 0.89 mM; GDP, 0.46 mM and GTP, 1.54 mM, in the case of ATP donor. The enzyme is inhibited by guanine, guanosine, dGDP, dGTP, N-bromosuccinimide, iodacetate, sodium borate and mercuric acetate.
Insights
A novel purine nucleotide pyrophosphotransferase enzyme from Streptomyces morookaensis was purified and characterized. This enzyme synthesizes purine nucleoside 3'-diphosphates, crucial for cellular signaling, and requires divalent cations for activity.
Area of Science:
- Biochemistry
- Enzymology
- Microbiology
Background:
- Purine nucleotides play vital roles in cellular processes.
- The synthesis of specific purine derivatives is essential for biological regulation.
- Streptomyces species are known producers of diverse enzymes with unique catalytic activities.
Purpose of the Study:
- To purify and characterize a novel purine nucleotide pyrophosphotransferase from Streptomyces morookaensis.
- To elucidate the enzyme's catalytic mechanism and substrate specificity.
- To investigate the enzyme's kinetic properties and cofactor requirements.
Main Methods:
- Purification of the enzyme to apparent homogeneity using standard biochemical techniques.
- Determination of molecular weight, isoelectric point, and optimal pH.
- Enzyme activity assays using various purine nucleotides and divalent cations.
- Kinetic analysis to determine Michaelis constants (Km) for substrates.
- Inhibition studies using specific chemical agents and purine derivatives.
Main Results:
- The enzyme is a monomeric protein with a molecular weight of 24-25 kDa and an isoelectric point of 6.9.
- It synthesizes purine nucleoside 5 -phosphate 3 -diphosphates (e.g., pppApp, pppGpp) by pyrophosphoryl group transfer.
- Optimal activity was observed with Mg2+ at pH > 10, and other divalent cations showed varying pH optima.
- Specific Michaelis constants were determined for AMP, ADP, GMP, GDP, and GTP.
- The enzyme was inhibited by guanine, guanosine, dGDP, dGTP, and several chemical agents.
Conclusions:
- Streptomyces morookaensis produces a unique purine nucleotide pyrophosphotransferase with significant synthetic capabilities.
- The enzyme's activity is dependent on divalent cations and exhibits specific substrate preferences.
- Understanding this enzyme provides insights into novel purine metabolism pathways and potential biotechnological applications.