Adenine nucleotide metabolism in Azotobacter vinelandii. Two metabolic pathways of AMP degradation |
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Authors: | Masataka Yoshino Takako Tsukada Keiko Murakami Keizo Tsushima |
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Institution: | (1) Department of Biochemistry, Yokohama City University School of Medicine, 232 Yokohama, Japan;(2) Present address: Department of Biochemistry, School of Pharmaceutical Science, Showa University, 142 Tokyo, Japan;(3) Present address: Department of Clinical Sciences, St. Marianna University School of Medicine, 213 Kawasaki, Japan |
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Abstract: | AMP-degrading pathways in Azotobacter vinelandii cells were investigated. AMP nucleosidase (EC 3.2.2.4) was rapidly synthesized and reached a maximum at 24 h, while the activity of 5-nucleotidase (EC 3.1.3.5) specific for AMP, which was negligible during the logarithmic phase of the growth, first appeared in 24 h-cultures, and reached a maximum after complete exhaustion of sucrose from the growth medium (70 h).Cell-free extracts of A. vinelandii of 48 h-cultures hydrolyzed AMP to ribose 5-phosphate and adenine in the presence of ATP, and adenine was deaminated to hypoxanthine. When ATP was excluded, AMP was dephosphorylated to adenosine, which was further metabolized to inosine, and finally to hypoxanthine. Hypoxanthine thus formed was reutilized for the salvage synthesis of IMP under the conditions where 5-phosphoribosyl 1-pyrophosphate was able to be supplied. These results suggest that the levels of ATP can determine the rate of AMP degradation by the AMP nucleosidase- and 5-nucleotidase-pathways. The role of ATP in the AMP degradation was discussed in relation to the regulatory properties of AMP nucleosidase, inosine nucleosidase (EC 3.2.2.2) and adenosine deaminase (EC 3.5.4.4). |
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Keywords: | AMP degradation Azotobacter vinelandii AMP nucleosidase 5-Nucleotidase" target="_blank">gif" alt="prime" align="BASELINE" BORDER="0">-Nucleotidase Regulation by ATP |
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