Agmatine iminohydrolase

Lathyrus sativus (enzyme has inherent activities of agmatine iminohydrolase, putrescine transcarbamylase, ornithine transcarbamylase and carbamate kinase [1]) [1]... 

Figure 22 Biosynthesis of polyamines through the arginine decarboxylase pathway. Putrescine derived from L-arginine through the action of three successive enzymes arginine decarboxylase (ADC), agmatine iminohydrolase (AIH), and N-carbamoylputrescine amidohydrolase (NCPAH).

Reaction 5 is catalyzed by arginine decarboxylase which has been found in barley (Smith, 1963). Agmatine can be converted to A-carbamoyl putrescine (reaction 6) by agmatine iminohydrolase (E.C. 3.5.3.12). This enzyme has been found in extracts of maize leaves and sunflower (Smith, 1969). The further hydrolysis of A/ -carbamyl putrescine to putrescine (reaction 7) is catalyzed by A-carbamyl putrescine amidohydrolase which has been found in barley leaf extracts (Smith, 1965). The enzyme activities catalyzing reactions 5 and 7 are increased several-fold in K-deficient barley leaves (Smith, 1963, 1965) which correlates well with the high level of putrescine accumulation in K-deficient barley. Further metabolism of putrescine is discussed by Smith, this series, Vol. 7, Chapter 9. 

Putrescine accumulation has been investigated in some detail and studies with radioactive precursors (see e.g.. Smith and Richards, 1%2 Smith, 1965) have established that it is synthesized from arginine (see Fig. 1). The mechanism underlying putrescine accumulation is uncertain although two of the biosynthetic enzymes, arginine decarboxylase, and iV-carbamyl pqtres-cine amidohydrolase exhibit two- to fourfold increases under conditions of K deficiency (Smith, 1%5). No increase was found to occur in the activity of agmatine iminohydrolase (Smith, 1969). 

Fig. 2. Biogenetic links between A primary metabolism and B the alkaloid-specific pathway. CAP, N-carbamoylputrescine GABA, 4-aminobutyric acid. Inhibitors DFMA, a-difluorome-thylarginine, HEH, /1-hydroxyethylhydrazine. Enzymes 1, arginine decarboxylase 2, agmatine iminohydrolase 3, JV-carbamoylputrescine amidohydrolase 4, diamine oxidase 5, pyrroline dehydrogenase (NAD+-dependent) 6, spermidine synthase 7, a putrescine-producing poly-amine oxidase (H H-insensitive) 8, homospermidine synthase 9, an HEH-sensitive polyamine oxidase...

ODC = ornithine decarboxylase PMT = putrescine methyltransferase MPO = methylputrescine oxidase OCT = ornithine carbamoyltransferase ADC = arginine decarboxylase AIH = agmatine iminohydrolase CPA =/v-carbaiTioylputrescine amidohydroiase SAM = S-adenosyl-methionine... 

Janowitz T, Kneifel H, Piotrowski M (2003) Identification and characterization of pltmt agmatine iminohydrolase, the last missing link in polyamine biosynthesis of plants. FEES Lett 544 258-261... 

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