Putrescine carbamoyltransferase activity in pea is associated with the ornithine carbamoyltransferase polypeptide and is not involved in putrescine synthesis under physiological conditions

Autor: H. F. Nichols, R. D. Slocum
Rok vydání: 1993
Předmět:
Zdroj: Plant Growth Regulation. 12:237-244
ISSN: 1573-5087
0167-6903
DOI: 10.1007/bf00027204
Popis: Putrescine carbamoyltransferase (PutCT) has been postulated to function in the synthesis of putrescine (Put) from an N-carbamoylputrescine (NCPut) intermediate in plants. In pea, PutCT activity was associated entirely with ornithine carbamoyltransferase (OCT) protein, which was purified to homogeneity using an immobilized transition-state analog inhibitor (δN-(phosphonacetyl)-L-ornithine). No evidence for a separate PutCT enzyme, similar to that in Streptococcus [15], or PutCT activity associated with a ‘putrescine synthase’-type multifunctional enzyme [13] was found. OCT carried out the carbamoylation of Put and other diamine and polyamine substrates inefficiently and at non-physiological pH (Put carbamoylation: pH 10.8 optimum, Vmax 0.11 μkat/mg protein, Km=6.7 mM for Put and 1.0 mM for carbamoyl-P), when compared with ornithine carbamoylation (pH 8.5 optimum, Vmax=313.9 μkat/mg protein, Km=4.4 mM for ornithine and 0.6 mM for carbamoyl-P). Different subcellular compartmentation of PutCT activity (chloroplast) and the NCPut substrate (cytosol), coupled with a thermodynamically-unfavorable reverse reaction (i.e., Put synthesis from NCPut), suggest that the OCT-associated PutCT activity does not significantly contribute to in vivo Put synthesis in plants.
Databáze: OpenAIRE
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