title: Guanine deaminase in rat liver and mouse liver and brain.
abstract: 1. The guanine deaminase in rat liver supernatant preparations was resolved into two fractions, A and B, on DEAE-cellulose columns. The two differed in electrophoretic mobility and in various properties. The most noteworthy distinction between A and B components was that the enzyme A activity showed a sigmoid dependence on substrate concentration whereas the enzyme B showed classical Michaelis-Menten kinetics. The K(m) value of enzyme A for guanine was 5.3mum and that of enzyme B 20mum. 2. The entire guanine deaminase activity of mouse liver was contained in the 15000g supernatant of iso-osmotic homogenates. 3. A reinvestigation of the behaviour of rat brain 15000g supernatant guanine deaminase isoenzymes revealed that one enzyme had sigmoidal kinetics and the other enzyme showed a hyperbolic response. 4. Of the guanine deaminase in mouse brain iso-osmotic sucrose homogenate 80% was recovered in the 15000g supernatant and the rest from the particles. The supernatant guanine deaminase was resolvable into two fractions on DEAE-cellulose columns. One enzyme showed sigmoidal kinetics whereas the other showed a hyperbolic response to increasing substrate concentration; the K(m) values for the reaction with guanine were respectively 5 and 66mum. 5. The particulate fractions of mouse liver and brain were devoid of any overt inhibitory activity.
mesh_terms: D000619:Aminohydrolases / Q000302:isolation & purification*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002499:Centrifugation, Density Gradient; D002848:Chromatography, DEAE-Cellulose; D004592:Electrophoresis, Starch Gel; D006147:Guanine; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D051379:Mice; D051381:Rats; D013053:Spectrophotometry; D013501:Surface-Active Agents
chemical_list: D013501:Surface-Active Agents; D006147:Guanine; D000619:Aminohydrolases