HYPOXANTHINE‐GUANINE‐PHOSPHORIBOSYL‐TRANSFERASE FROM RAT BRAIN (PURIFICATION, KINETIC PROPERTIES, DEVELOPMENT AND DISTRIBUTION)

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Abstract
Hypoxanthine‐guanine‐phosphoribosyltransferase (HGPR Tase; ECC 2.4.2.8) has been purified from rat brain 650‐fold to about 50 per cent purity by conventional methods. An isoenzyme pattern of at least three components is observed on DEAE‐cellulose chromatography. On polyacrylamide disc electrophoresis only one sharp band of enzyme activity can be detected. The apparent Km‐value determined for phosphoribosylpyrophosphate (PRPP) is about 0.2 mM. The product, GMP, and also GDP, GTP, UMP, CMP, AMP and ATP are competitive inhibitors with respect to PRPP. Inhibition by a number of other nucleotides has also been investigated. Studies on the development of enzyme activity in the brain of the young rat show that a rapid increase occurs during the first 15‐20 days of life and reaches a plateau thereafter. The regional distribution of HGPRTase activity in adult rat brain is more homogenous than that reported for human brain. The enzyme is predominantly a constituent of the soluble supernatant fraction, but can also be found in carefully washed synaptosomes. An antiserum against rat brain HGPRTase obtained from rabbits inhibits this enzyme to about 30 per cent of control activity, but does not crossreact with HGPRTases from rabbit or human erythrocytes.