Isolation and characterization of AMP deaminase from mammalian (rabbit) myocardium.
AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) is a ubiquitous enzyme in eukaryotes, which may play a role in ATP catabolism during myocardial ischaemia. We report isolation of AMP deaminase from rabbit myocardium with a 19% recovery and a 650-fold enrichment, using a newly devised protocol involving sequential cation-exchange, gel-permeation and affinity chromatographies. The cardiac AMP deaminase preparation described was electrophoretically and chromatographically homogeneous and contained one unique N-terminal residue (leucine). The isolated enzyme was sensitive to various cations (K+, Mg2+, Ca2+). The pH optimum of purified cardiac AMP deaminase was 6.8, its pI was 6.5, and it displayed substrate-specificity toward 5'-AMP. The subunit molecular mass of rabbit heart AMP deaminase on SDS/PAGE (81 kDa) and the holoenzyme molecular mass as estimated by non-denaturing size-exclusion h.p.l.c. (330 kDa) indicated that the native enzyme was a tetramer. Cardiac AMP deaminase displayed a sigmoidal substrate-saturation curve in the presence of 100 mM KCl. Apparent Michaelis constants were a Km of 5.8 mM AMP and a Vmax. of 11.1 mumol/min per mg of protein. ATP and ADP were positive allosteric effectors of cardiac AMP deaminase: the apparent Km was decreased to 1.7 mM by 1.0 mM ATP. The enzyme was inhibited by GTP, coformycin, coformycin 5'-phosphate, palmitoyl-CoA, inorganic phosphate compounds, and the metal chelator o-phenanthroline. No inhibition either by product nucleotide (IMP) or by nicotinamide nucleotides was detected when these agents were examined at concentrations up to 2.5 mM. We conclude that this enzyme preparation offers a means by which the kinetic mechanism and regulation of mammalian cardiac AMP deaminase may be directly investigated.
Thakkar
J K
JK
Research Department, CIBA-GEIGY Corporation, Summit, NJ 07901.
Janero
D R
DR
Yarwood
C
C
Sharif
H
H
Hreniuk
D
D
D000659:AMP Deaminase / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D011817:Rabbits; D013379:Substrate Specificity
D000596:Amino Acids; D000659:AMP Deaminase