Crystalline adenylate kinase from carp muscle

Area of Science:

• Biochemistry
• Enzymology
• Structural Biology

Background:

• Adenylate kinase (EC 2.7.4.3) plays a crucial role in cellular energy metabolism.
• Carp muscle is a potential source for adenylate kinase isolation.

Purpose of the Study:

• To develop an improved isolation procedure for carp adenylate kinase.
• To characterize the physical and chemical properties of carp adenylate kinase.
• To investigate the active site of carp adenylate kinase.

Main Methods:

• Phosphocellulose chromatography with dilute substrates for enzyme elution.
• Hexokinase--pH-stat assay for specific activity determination.
• Dodecylsulfate gel electrophoresis, isoelectric focusing, and gel filtration for homogeneity assessment.
• X-ray crystallography for crystal structure determination.
• Amino acid composition analysis and tryptic hydrolysis for peptide mapping.

Main Results:

• An improved isolation procedure yielded carp adenylate kinase with 60% overall yield and high specific activity (3550 units/mg).
• The enzyme preparation was found to be essentially homogeneous with a molecular weight of 22000, isoelectric point of pH 5.9, and specific absorbance of 6.9.
• Crystals of carp adenylate kinase belong to space group P4-1-22 or P4-3-22.
• Amino acid analysis revealed the absence of tryptophan and cystine, with single residues of cysteine and histidine potentially located at the catalytic center.

Conclusions:

• The optimized isolation protocol provides a highly pure and active carp adenylate kinase.
• The determined physical and structural properties provide a basis for further functional studies.
• The presence of cysteine and histidine residues near the catalytic center suggests their involvement in enzyme activity.