Deamination of adenosine by extracts of Penicillium politans NRC‐510

Abstract

Cell-free extracts of nitrate-grown Penicillium politans NRC-510 could catalyze the hydrolytic deamination of adenosine to inosine maximally at pH 6.0 and 45 degrees C. However the same extracts could not catalyze the N-glycosidic bond cleavage of adenosine at pH 4.0, 6.0 and 8.0. Incubation of the extracts at 55 degrees C for 30 minutes caused about 31% loss in activity whereas incubation of the extracts at 60 degrees C for 15 minutes caused a complete loss of enzyme activity. Results indicated the absence of the involvement of sulfhydryl groups in the catalytic site of adenosine deaminase. The enzyme is inhibited by ethylene diamine tetraacetate indicating that adenosine deaminase is a metalloenzyme. MnCl2 and MgCl2 had a remarkable activating effect, whereas HgCl2, CaCl2 and ZnSO4 showed an inhibitory effect on enzyme activity. Dialyzing the extracts for 24 hours significantly increase deaminase activity by about 33%. The apparent K(m) value was calculated for adenosine and found to be 3.63 x 10(-3) M, which indicates high affinity of adenosine deaminase for its substrate adenosine.

Ribonucleoside Hydrolases–Structure, Functions, Physiological Role and Practical Uses

“…In the case of other eukaryotes, nucleoside hydrolases have been found in yeast [ 28 ], fungi [ 29 , 30 , 31 , 32 , 33 ], nematodes [ 34 , 35 ], insects [ 36 ], and fish [ 37 ]. In addition, genes homologous to various Rih hydrolases have been found in other eukaryotes, but the enzymes encoded by these genes have not been studied.…”

“…An example of a reaction for this type of hydrolase is shown in Figure 2 . Hydrolases of this type are found in archaea [ 50 , 51 , 52 , 53 ], protozoa [ 3 , 5 , 12 , 13 , 14 ], some bacteria [ 20 ], fungi [ 30 , 33 ], and insects [ 36 ]. Hydrolases of the third type are nonspecific purine–pyrimidine hydrolases.…”

“…In general, for hydrolases from mesophilic organisms, the optimum catalytic activity is observed at 30–40 °C (with the exception of some hydrolases from thermotolerant organisms, for example, those mentioned above), and when heated above 50 °C, these enzymes lose 50% of their activity in less than an hour [ 30 , 32 , 37 , 54 ]. Hydrolases from thermotolerant organisms are usually more thermostable, able to withstand incubation at 50–60 °C without significant loss of activity for an hour or even several hours [ 33 , 58 , 59 , 63 ].…”

Untargeted Metabolomics Analysis of Serum Metabolites in Zucker Diabetic Fatty Rats

“…The key enzyme in this pathway, adenosine deaminase, is widely classified in human tissues. It has a great impact in the reproduction and differentiation of lymphoid cells, and seems to impact different stages of the maturation of the immune system [15,16]. In addition to this, to generate energy continuously, many organisms recycle adenosine nucleotides by repeating the process of adenosine nucleotides degradation II and the adenine and adenosine salvage VI.…”