Hirayama C, Saito H, Konno K, Shinbo H. Purification and characterization of NADH-dependent glutamate synthase from the silkworm fat body (Bombyx mori).
INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 1998;
28:473-482. [PMID:
9718680 DOI:
10.1016/s0965-1748(98)00019-8]
[Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
NADH-dependent glutamate synthase (Nadh-Gogat; EC 1.41.14) was purified 766-fold from the fat body of 5th instar larvae of the silkworm with a final specific activity of 13.8 units/mg protein by a produce including ammonium sulfate fraction, Q-Sepharose HP ion exchange column chromatography, Blue Sepharose FF affinity column chromatography and Superdex 200 HR gel filtration. The purified enzyme yielded a single band corresponding to a molecular mass of 195kDa by SDS-polyacrylamide gel electrophoresis. Molecular mass of the native enzyme was estimated to be 190 kDa by Superdex 200HR gel filtration, suggesting that the enzyme is composed of a monomeric polypeptide. The enzyme showed an absorption spectrum with maximum values at 272, 375, and 435 nm, suggesting the presence of a flavin prosthetic group in the enzyme. The N-terminal amino acid sequence showed a high similarity to those of other GOGATs from plants, yeast and bacteria, but no similarity to other known proteins was detected. The enzyme exhibited a strong specificity to the electron donor and substrates; NADH as electron donor, 2-oxoglutarate as amino acceptor and glutamine as amino donor were essential for the catalytic activity. The optimum pH was around 7.5, at which Km values for 2-oxoglutarate, glutamine and NADH were 17, 220 and 5.7 micro M, respectively. Azaserine, 6-diazo-5-oxonorleucine and p-chloromercuribenzoic acid were strong inhibitors of the activity. These result show that NADH-GOGAT in the silkworm fat body strongly resembles other eukaryotic NADH-GOGATs, suggesting that it plays a significant role in ammonia assimilation in the same manner as the other enzymes.
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