1887

Abstract

Summary: Carboxynorspermidine synthase, mediates the nicotinamide-nucleotide-linked reduction of the Schiff base HN(CH)N = CHCHCH(NH)COOH. This is formed from l-aspartic β-semialdehyde (ASA) and 1,3-diaminopropane (DAP) and is reduced to carboxynorspermidine [HN(CH)NH(CH)CH(NH)COOH], an intermediate in the novel pathway for norspermidine (NSPD) biosynthesis. The enzyme was purified to apparent homogeneity from and characterized. The overall purification was about 1800-fold over the crude extract, with a yield of 33%. The enzyme displayed an apparent of 93500 × 1000 by gel filtration and 45100 × 500 by SDS-PAGE, indicating that the native form is probably composed of two subunits of similar size. The specific activity of the purified enzyme was 31·0 μmol carboxynorspermidine produced min (mg protein). The enzyme was activated by dithiothreitol, and inhibited by SH-reactive compounds. The pH and temperature optima were 7·25-7·5 and 37 °C, respectively. The value for the Schiff base was 4·68 mm, measured by varying the ASA concentration while keeping the DAP concentration constant. Putrescine was slightly active as a substrate, forming carboxyspermidine (at about 7% of the rate of DAP), but ethylenediamine, cadaverine and d-ASA were inert. The value for NADPH was 1·51 mm. NADH was a much poorer cofactor than NADPH. When was grown in the presence of 5 mm-NSPD, the specific activity of this enzyme was reduced by ∼70%. NSPD also repressed two other enzymes responsible for its biosynthesis, 2,4-diaminobutyrate decarboxylase and carboxynorspermidine decarboxylase.

Loading

Article metrics loading...

/content/journal/micro/10.1099/00221287-137-7-1737
1991-07-01
2019-10-20
Loading full text...

Full text loading...

http://instance.metastore.ingenta.com/content/journal/micro/10.1099/00221287-137-7-1737
Loading
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error