A Mammals B Fangi 3-AAP ARG ARG ORN PUT SPD -ORN PUT SPD SAM- dcSAM MTA MTA SAM dcSAM SAMDC MTA MTA SAMDC C Bacteria D Plants AGMATINE ARG -ADC AGMATINE AgUH Arginase UREA NCP NCPase ORN PUT SPD ORN PUT SPD SAM-SAMDC→deSAM MTA SAM- dcSAM SAMDC MTA MTA Fig.1.Schematic representation of the polyamine biosynthetic pathway and its variants in mammals(A),fungi(B),bacteria(C). and plants (D).In panels B and C,the dotted lines represent the endogenous biosynthesis of ornithine and arginine;in mammals (panel A),the ornithine used for polyamine biosynthesis comes largely from the diet.Abbreviations:ARG,arginine;3-AAP,3-acet- amidopropanal;AcCoA,acetyl coenzyme A;AcSPD,acetylspermidine;AcSPM,acetylspermine:ADC,arginine decarboxylase; AgUH,agmatine ureohydrolase;AIH,agmatine iminohydrolase;dcSAM,decarboxylated SAM;FBI,feedback inhibition (of argin- ine on ornithine biosynthesis);MTA,methylthioadenosine;NCPase,N-carbamoylputrescine amidohydrolase;ORN,ornithine; ODC,ornithine decarboxylase;PUT,putrescine;SAMDC,SAM decarboxylase;SPD, spermidine;SPM,spermine果树专业硕士生课程-yao1