Neurospora crassa molecular weight

PolyPs are present in the cell envelopes of the lower eukaryotes, where their contents may vary depending on the cultivation conditions. PolyP was found at first in the cell envelope of Neurospora crassa (Krascheninnikov et al., 1967 Kulaev et al., 1970) and domycesmagnusii (Kulaev etal, 1967 Kulaev and Afanasieva, 1970). This high-molecular-weight PolyP was located outside of the cell, adjacent to the outer side of the cytoplasmic membrane. 

Nitrite reduction in assimilatory nitrate-reducing Neurospora crassa, Torulopsis nitratophila, Azotobacter vinelandii, and Azotobacter chro-ococcum appears to be catalyzed by enzyme systems which require flavin and metals. The enzyme from N. crassa has been partially purified, and its molecular weight has been estimated to be 300,000 (344, 346, 351, 367). The enzyme reduces both nitrite and hydroxylamine to ammonia and utilizes NADH or NADPH as electron donor. It is reported to be a FAD-dependent enzyme and to contain iron, copper, and active thiol (346, 367). Three moles of NADH are oxidized per mole of nitrite reduced to ammonia. It has been suggested that the reduction of nitrite occurs in three steps, each involving two electrons. Thus, hyponitrite and hydroxylamine have been proposed as successive intermediates in the re-... 

A band with a molecular weight of 25 000 of the bacterial oxidoreductase has been identified with the high-potential Fe-S protein, by means of cross reaction with a monospecific antibody against the analogous electron carrier from Neurospora crassa mitochondria. The existence of this type of Fe-S center in photosynthetic bacteria was first discovered by ESR spectroscopy [125] and its involvement in photosynthetic electron transport was demonstrated. The midpoint potential in Rps. sphaeroides is 0.285 V, and is pH dependent above pH 8, with a decrease of 60 mV per pH unit [125]. 

The biosynthesis of the adenine nucleotide carrier has been studied most extensively in Neurospora crassa. The carrier isolated from Neurospora mitochondria is very similar to the carrier isolated from mammalian mitochondria [78]. Its molecular weight, subunit structure, amino acid composition, hydrophobicity and inhibitor specificity are remarkably similar to the mammalian heart and liver carriers. Specific antibodies to the Neurospora carrier have been raised in rabbits [79]. 

Subdivision below the monomer level occurs in the presence of sodium dodecyl sulfate and thiols (mercaptoethanol). The oxidase is thus identified as a multisubunit protein. Both yeast 57, 73) and Neurospora crassa (74) oxidases were shown to be composed of seven subunits. Bovine heart oxidase, on the other hand, has been reported to have between two 75, 76) and six 57, 76) subunits. The subunits from yeast have molecular weights in the range of I, 40,000 II, 33,000 III, 22,000 IV, 14,000 V, 12,700 VI, 12,700 and VII, 4,600 57, 77). The situation for bovine heart is less clear but the six subunits are reported to have molecular weights around I, 40,000 II, 25,000 III, 19,000 IV, 14,000 V, 10,000 and VI, 8,000 76). When fewer than six subunits are found, their molecular weights invariably correspond to some of the six reported 75-78). The subunit sizes differ for yeast and bovine heart 57). That the protein compositions differ is also reflected in the failure of antibodies against subunits II and VI of yeast oxidase to cross-react with bovine heart oxidase 79). 

Further data were obtained by Weiss et al. (1971) with Neurospora crassa. Chromatography of mitochondrial protein labeled in vivo in the presence of cycloheximide (CH), yielded fractions containing difilerent amounts of radioactivity. The fraction of highest specific radioactivity was pure and enzymically active cytochrome oxidase. Separation of the polypeptide chains of this enzyme by SDS gel electrophoresis revealed five protein bands of which, in the presence of CH, only one polypeptide was highly labeled. Similar results were obtained with cytochrome oxidase from Locusta migratoria (Weiss et al, 1972). Here seven polypeptide chains were obtained. One, with a molecular weight of about 19,000, was labeled in the presence of CH and may be a product of mitochondrial protein synthesis. 

Although the biogenesis of cytochrome b has not been closely examined in yeast, studies on Neurospora crassa have shown that in this organism, both the mitochondrial and cytoplasmic protein-synthesizing systems contribute to the cytochrome b complex. Cytochrome b probably contains two polypeptide types of molecular weight 30,000. Inhibition studies have shown that only one of these is translated on mitochondrial ribosomes (see Chapter 5). 

The structural and catalytic characteristics of tryptophan synthetase are under active investigation. The enzyme has a molecular weight of 135,000 and is composed of four subunits held together by noncovalent bonds. Floss and coworkers (361) determined the steric course of the tryptophan synthetase catalyzed reaction between serine and indole, using the enzyme isolated from Neurospora crassa. The reaction was... 

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