124 O- MEYERHOF, R. SHATAS, A. KAPLAN VOL. 12 (1953) 



The heat inactivation of the enzyme was studied by preincubation at 33° C and 

 pH 7. A loss of activity up to 40 percent was observed after 3 h ; however, the activity 

 was completely preserved in a 50% solution of glycerol. A similar stabilization by 

 glycerol was previously described by Meyerhof and Ohlmeyer in the case of adenosine 

 triphosphatase^^. 



TABLE III 



ACTIVITY OF ENZYME TOWARDS DIFFERENT PHOSPHATES 

 UNDER SIMILAR EXPERIMENTAL CONDITIONS 



Substrate Relative Activity 



Pyrophosphate 2 



Trimetaphosphate i 



Hexametaphosphate 0.3 



We did not find any evidence that the enzymic cleavage of trimetaphosphate passes 

 through an intermediate step of pyrophosphate. By addition of crystalline pyrophos- 

 phatase the rate of hydrolysis did not increase (Table IV). 



Even if our enzyme contained pyrophosphatase, the Qp of the added crystalline 

 pyrophosphatase was more than 50,000 times higher. 



TABLE IV 



THE RATE OF ENZYMIC HYDROLYSIS OF TRIMETAPHOSPHATE 

 WITh'aND WITHOUT ADDITION OF CRYSTALLINE PYROPHOSPHATASE 



„ Orthophosphate formed in 



Enzyme -^ . <: .■' , 



' 10 mm in micromoles 



Metaphosphatase 6.4 



Metaphosphatase and cryst. 6.2 



pyrophosphatase 

 Metaphosphatase; cryst. 



pyrophosphatase added 



after 5 min. incubation 6.4 



Unlike the pyrophosphatase^^, the trimetaphosphatase is not inhibited by substrate 

 concentration as high as 0.2 M as shown in Table V. 



TABLE V 



RATE OF ENZYMIC HYDROLYSIS OF TRIMETAPHOSPHATE AS FUNCTION OF SUBSTRATE CONCENTRATION 



If the duration of incubation did not exceed i h, the kinetics of enzymic hydrolysis 

 followed closely that of a reaction of first order (Fig. i). After 3 h the rate of hydrolysis 



References p. I2j . 



