[Liver and brain guinea-pig guanine aminohydrolase (author's transl)]

Guinea-pig brain guanine aminohydrolase (E.C. 3.5.4.3) (M = 120,000 +/- 5,000 daltons) only exhibited one active electrophoretic band; its mobility is similar with that observed for the guinea-pig liver molecular form III. Both forms appear to have coincident activity with pH, as well as an analogous thermal stability and Km values with different substrates showing a different behaviour with the molecular form I of guinea-pig liver enzyme. Brain guanine aminohydrolase and liver molecular form III have similar pK'a values suggesting the participation of histidine and cysteine (-SH) in the enzymatic catalysis. The competitive inhibition by p-chloromercuribenzoate may corroborate the intervention of the last-one.