Effects ofSpecific Antibodies on theCatalytic Activity of L-Asparaginase fromSerratia marcescensandEscherichia coli

Rabbitantisera against highly purified L-asparaginase fromSerratia marcescensandfromEscherichia coli showed up to60%inhibition ofthe catalytic amidohydrolysis ofL-asparagine whencombined withthehomologous enzyme. Thisinhibition was diminished somewhat against theheterologous enzyme. Kinetic studies inthepresenceofthese antisera showed an increased Km,&P forbothhomologous andheterologous enzymes usingL-asparagine as substrate. Incontrast, kinetic studies employing thepoorsubstrate, L-glutamine, showedactivation attributable tospecific antibodies. Thiswas seen inlower KmaPPvalues andup totwofold increases intheVi.. overthenormalrabbit serum controls. Thehighdegree ofcross-inhibition ('80%) andthelowdegree of cross-reactivity inthequantitative precipitin test(-34%) suggest thatthese two enzymespossessstructural similarities located mainly intheregions ofthecata- lytic sites.