JBC, Vol. 250, Issue 17, 6653-6658, Sep, 1975
Rat muscle 5'-adenylic acid aminohydrolase. I. Purification and subunit structure
C. J. Coffee and W. A. Kofke
AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) has been purified to
apparent homogeneity from rat muscle. The preparation exhibits a single
polypeptide band with a molecular weight of 60,000 on polyacrylamide gel
electrophoresis in the presence of sodium dodecyl sulfate. The enzyme has a
sedimentation coefficient of 11.3 S. Analysis by sedimentation equilibrium
techniques showed the nat-ive enzyme to have a molecular weight of 238,000,
whereas the enzyme, when analyzed in 6 M guanidine hydrochloride and 10 mM
2-mercaptoethanol, had a molecular weight of only 59,500. The amino acid
composition of the enzyme was determined and peptide mapping was performed
on a tryptic digest of S-carboxymethylated enzyme. NH2-terminal analysis by
both the dansylation and cyanate procedures failed to identify a free NH2
terminus. Treatment of the enzyme with carboxypeptidase A resulted in the
release of approximately 0.5 mol each of valine and leucine per 60,000 g of
enzyme. The data presented indicate that hte native enzyme has a tetrameric
structure consisting of four polypeptide chains each having a molecular
weight of 60,000. The COOH-terminal analysis can be interpreted either as
an indication of subunit heterogeneity or as a result of incomplete
digestion of a -X-Leu-Val sequence at the end of a single type of
polypeptide chain. Tryptic peptide maps strongly support the latter
interpretation and suggest that the subunits are essentially identical.