Purification and Regulatory Properties of Mung Bean (Vigna Radiata L.) Serine Hydroxymethyltransferase

Abstract

Serine hydroxymethyltransferase, the rirst enzyme in the pathway for interconversion of C1 fragments, was purified to homogeneity for the first time from any plant source. The enzyme from 72-h mung bean (Vigna radiata L.) seedlings was isolated using Blue Sepharose CL-6B and folate-AH-Sepharose4B affinity matrices and had the highest specific activity (1. The sigmoid saturation pattern of H4folate (nH = 2.0), one of the substrates, the abolition of sigmoidicity by NADH, an allosteric positive effector (nH = 1.0) and the increase in sigmoidicity by NAD+ and adenine nucleotides, negative allosteric effectors (nH = 2.4) clearly established that this key enzyme in the folate metabolism was an allosteric protein. Further support for this conclusion were the observations that (a) seine saturation exhibited an intermediary plateau region; (b) partial inhibition by methotrexate, aminopterin, O-phosphoserine, DL-a-methylserine and DL-O-methylserine; (c) subunit nature of the enzyme; and (d) decrease in the nH value from 2.0 for Hfolate to 1.5 in presence of L-serine.These results highlight the regulatory nature of mung bean serine hydroxymethyltransferase and its possible involvement in the modulation of the interconversion of folate coenzymes.The major storage form of folate coenzymes in plants is N5-methyltetrahydrofolate (21). Although this compound is present in abundant quantities the metabolism of C1 compounds and the 'This investigation was supported from a research

Serine hydroxymethyltransferase from spinach leaf mitochondria. Purification and characterization

“…Blue Sepharose CL-6B and Folate AH-Sepharose, and a hydroxylapatite column gave a preparation with a specific activity of 7.8 nmol (mg protein) ' min ' (Tab. I) which is similar to the specific activity reported for the rabbit liver SHMT [ 10 nmol (mg protein)"' min ';Schirch et al 1985] but significantly higher than the mung bean enzyme [1.33 ixmol (mg protein) ' min '; Rao and Rao 1982).…”

“…An improved knowledge of this mitochondrial enzyme could give us a better understanding of photorespiration. SHMT has been purified and characterized from various non-photosynthetic sources (O'Connor and Hanson 1975, Rao and Rao 1982, Schirch 1982, Schirch et al 1985. It is of interest to see if this plant enzyme behaves in a similar way as, for example, its mammalian counterpart for which the reaction is generally believed to be most significant in the direction from serine to glycine (Schirch 1982), which is the opposite direction compared to photorespiration.…”

Effects of Antibiotics that Inhibit the Bacterial Peptidoglycan Synthesis Pathway on Moss Chloroplast Division

“…There are two reports on the relationship between these antibiotics and eukaryotic plant enzymes. The antibiotic D-cycloserine inhibits the activity of serine hydroxymethyltransferase isolated from mung bean seedlings (Rao and Rao 1982). Mújica-Jiménez et al (1998) reported that fosfomycin acts as a potent, reversible non-essential activator of phosphoenolpyruvate carboxylase from C 4 maize leaves by binding to the same allosteric site as glucose-6-phosphate.…”

Relations entre la photosynthèse et l'assimilation de l'azote

“…Dans les mitochondries, la condensation de 2 molécules de glycine, catalysée par la sérine hydroxyméthyltransférase, aboutit à la sérine (folbert, 1979;Rao et Rao, 1982) ; dans cette réaction une molécule de C0 2 et une de NH 3 sont libérées; le C0 2 est émis à l'extérieur en atmosphère sans gaz carbonique ou recyclé dans le métabolisme photosynthétique en air normal (Gaudillère, 1981) ; l'ammonium est immédiatement repris par le jeu de la glutamine synthétase-glutamate synthase étudié dans le paragraphe précé-dent. Lips (1979) traite de la photorespiration dans le métabolisme des nitrates.…”