HETEROGENEITY OF GLUTAMINE SYNTHETASE POLYPEPTIDES IN Phaseolus vulgaris L

Abstract

Glutamine synthetases from roots, nodules, and leaves of Phaseolus vulgaris L. have been purified to homogeneity and their polypeptide composition determined.The leaf enzyme is composed of six polypeptides. The cytosolic fraction contains two 43,000 dalton polypeptides and the chloroplastic enzyme is formed by four 45,000 dalton polypeptides. Root glutamine synthetase consists only of the same two polypeptides of 43,000 dalton that are present in the leaf enzyme. The nodule enzyme is formed by two polypeptides of 43,000 dalton, one is common to the leaf and root enzyme but the other is specific for Nrfixing nodule tissue. The two glutamine synthetase forms of the nodule contain a different proportion of the 43,000 dalton polypeptides.

Subunit Composition of Glutamine Synthetase Isozymes from Root Nodules of Bean (Phaseolus vulgaris L.)

“…Lara et al (13) reported that both GS,, and GSn2 have f and y subunit polypeptides, although the amount of y in GS.2 is relatively small in comparison to (3. This discrepancy between their and our results may be because we have purified GSn2 to homogeneity. Lara The native GS consists of eight subunit polypeptides, and in the root nodules they are of two different types (3,13). We proposed earlier that a total of nine isozymes can be generated assuming the assembly of, and y subunit polypeptides into the holoenzyme is a random process (23).…”

“…A small source is in the infected cells, and a large source is in the uninfected cells, which for the purpose of this discussion are all nodule cells except the infected ones. The (3 polypeptide is found in the leaves, roots, and nodules (7,13). Its gene appears to be constitutively expressed (7).…”

“…The physical and kinetic properties of GS., and GSn2 are similar (3). The holoenzyme of both isoforms have identical mol wt (380,000 D), and are both comprised of eight subunit polypeptides of 41,000 D. Lara et al (13) reported that GS., and GSn2 are comprised of two different types of subunit polypeptides (,3 and y). The polypeptides have identical mol wt but different isoelectric points.…”

“…In an organ such as the bean nodule, there are two different types of GS subunit polypeptides (13). Since the GS holoenzyme consists of eight polypeptides (3), it is not known whether the eight subunit polypeptides of the holoenzyme must be identical (i.e.…”

Atividade das enzimas redutase do nitrato e glutamina sintetase em cafeeiro arábica.

“…Tanto a isoforma da GS presente nas raízes como nas folhas são compostas de polipeptídeos denominados α e β (Lara et al, 1984). Nos nódulos, as subunidades que formam a enzima são do tipo β e α, as quais diferem entre si no ponto isoelétrico, mas não em relação ao tamanho.…”