Bis-(5'-guanosyl) tetraphosphatase in rat tissues.

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Abstract
The occurrence and distribution of bis-(5''-guanosyl) tetraphosphatase activity towards dinucleoside tetraphosphates between the 27,000 g supernatant and sedimented fraction were studied in liver, kidney, brain, muscle and intestinal mucosa from rat. The P1P4-bis-(5''-guanosyl) tetraphosphate-hydrolysing activities found in total homogenates were 0.77, 1.44, 0.39, 0.36 and 2.14 units (.mu.mol/min) per g, respectively. The activities found in the 27,000 g-sedimented fractions were 74, 49, 11, 4 and 96% of those present in the homogenates, respectively. The properties of the soluble enzymes were investigated. All of them have low Km values for P1P4-bis-(5''-guanosyl) tetraphosphate (from 2-50 .mu.M), are competitively inhibited by guanosine 5''-tetraphosphate with Ki values from 10-160 nM, have MW of .apprx. 21,000, require Mg2+ or Mn2+ and are inhibited by Ca2+. These properties show that bis-(5''-guanosyl) tetraphosphatase, an enzyme previously characterized in Artemia salina and rat liver, is present in all rat tissues examined. The inhibition of the enzyme by Ca2+ could be related to the effect of P1P4-bis-(5''-adenosyl) tetraphosphate as a trigger of DNA synthesis.