598 G. SCHMIDT 



yH Optimum. 5'-Adenylic acid deaminase has a sharp optimum at pH 

 5.9. 



Extractability. 5'-Adenyhc deaminase is easily extracted from minced 

 muscle by 2 % solutions of sodium bicarbonate or, to a lesser extent, by 

 water. Very little of the enzyme is extracted by 0.85% sodium chloride 

 solution. Removal of soluble proteins by exhaustive extraction of minced 

 rabbit muscle with the latter solution, and subsequent extraction of the 

 residue with 2% sodium bicarbonate solution, yields a highly active de- 

 aminase extract, free of myoglobin, which represents a suitable starting 

 material for further purification. 



These solubility properties are probably responsible for the fact that 

 purified myosin preparations frequently exhibit deaminating activity 

 toward 5'-adenylic acid.^^ The association of this deaminase with myosin, 

 however, is much looser than that of the Ca-activated adenosinetriphos- 

 phatase. At present, it is hardly justifiable to consider adenylic deaminase 

 activity as an inherent property of myosin,!^^ particularly in view of the 

 absence of adenylic acid deaminase activity in heart muscle. 



2. Enzymic Deamination of the Guanine Group: Guanase, Guanosine 

 Deaminase, Guanylic Acid Deaminase 



Unlike the adenine group, the guanine group can be deaminated enzymi- 

 cally by many tissues of higher animals in the form of the free base as well 

 as in that of its riboside.i^^a Aqueous extracts of fresh rabbit liver or of acetone 

 powders prepared from this tissue are capable of deaminating guanylic acid, 

 guanosine, and guanine. The crude, as well as the purified, enzyme prep- 

 arations used in these investigations contained, in addition, phosphatase, 

 nucleoside phosphorylase, and possibly enzymes cleaving the purine-ribose 

 linkage of nucleotides. The available evidence^^^ "^ does not permit a deci- 

 sion of the question as to whether or not guanosine and guanylic acid are 

 deaminated before the cleavage of the guanine-ribose linkage. 



Specificity of Guanase. Guanase is highly, but not absolutely, specific for 

 guanine. According to Hitchings and Falco,"^ the enzyme also deaminates 

 1-methylguanine. Roush and Norris"^ found that highly purified guanase 

 preparations prepared from rat liver according to Kalckar^^^^ deaminate 

 azaguanine. The deamination of azaguanine is competitively inhibited by 

 guanine. Measurable inhibitory effects of some pteridine derivatives (xan- 



I'l V. Sz. Hermann and G. Josepovits, Nature 164, 865 (1949). 



"2 B. A. Askonas, Biocheyn. J. 48, 42 (1951). 



1"* For older references, see W. Jones, "Nucleic Acids," p. 70. Longmans Green & 



Co., London, 1920. 

 1" G. Schmidt, Z. physiol. Chem. 208, 185 (1932). 

 "4 Y. Wakabayashi, J. Biocheyn. (Japan) 28, 185 (1938). 



"6 G. H. Hitchings and E. A. Falco, Proc. Natl. Acad. Sci. U. S. 30, 294 (1944). 

 "6 A. Roush and E. R. Norris, Arch. Biochem. 29, 124 (1950). 



