The structure and genetic control of a new class of disulphide-linked proteins in wheat endosperm

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of unreduced total protein extracts from the endosperm of hexaploid wheat revealed three high molecular weight protein bands (triplet bands) in a zone of heavy background streaking. Electrophoretic examination of 135 hexaploid cultivars showed at least five different patterns of these triplet bands. Nine durum wheat cultivars showed a single band only. Analysis of nullisomic-tetrasomic and ditelocentric lines of 'Chinese Spring' wheat revealed that the slowest moving band (Tri-1) of the triplet was controlled by gene(s) on chromosome arm 1DS and the fastest moving band (Tri-3) by 1AS. The band with intermediate mobility (Tri-2) was found to be a hybrid aggregate of the subunits controlled by 1DS and 1AS. Using a non-reducing/reducing form of 2-dimensional (2-D) electrophoresis, these triplet bands were shown to be heterotetramers of four subunits designated D (M.W. 58,000), δ (22,000), A (52,000) and α (23,000) where Tri-1=DδDδ, Tri-2 = DδAα and Tri-3 = AαAα. With very low concentrations of 2-mercaptoethanol (ME), the tetramers dissociated into dimeric subunit pairs (Dδ, Aα), the monomers being observed with higher concentrations of ME. The structure of these subunit pairs resembles that of the subunit pairs in the globulin storage proteins of oats and some legumes. The 2-D method employed in this study was useful also for separating low molecular weight (LMW) subunits of glutenin from the monomeric gliadins which have similar electrophoretic mobility in 1-D separation. It was shown that at least four of these LMW glutenin subunits are controlled by genes on 1DS and 1AS and at least one subunit is controlled by gene(s) on 1BS. This electrophoretic separation method has proven useful in understanding the aggregation behaviour of the seed proteins of wheat.

Proteins Associated with Adaptation of Cultured Tobacco Cells to NaCl

Cultured tobacco cells (Nicotiana tabacum L. cv Wisconsin 38) adapted to grow in medium containing high levels of NaCl or polyethylene glycol (PEG) produce several new or enhanced polypeptide bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The intensities of some of the polypeptide bands (molecular weights of 58, 37, 35.5, 34, 26, 21, 19.5, and 18 kilodaltons) increase with increasing levels of NaCl adaptation, while the intensities of other polypeptide bands (54, 52, 17.5, and 16.5 kilodaltons) are reduced. Enhanced levels of 43- and 26-kilodalton polypeptides are present in both NaCl and PEG-induced water stress adapted cells but are not detectable in unadapted cells. In addition, PEG adapted cells have enhanced levels of 29-, 17.5-, 16.5-, and 11-kilodalton polypeptides and reduced levels of 58-, 54-, 52-, 37-, 35.5-, 34-, 21-, 19.5-, and 18-kilodalton polypeptide bands.Synthesis of 26-kilodalton polypeptide(s) occurs at two different periods during culture growth of NaCl adapted cells. Unadapted cells also incorporate (35)S into a 26-kilodalton polypeptide during the later stage of culture growth beginning at midlog phase. The 26-kilodalton polypeptides from adapted and unadapted cells have similar partial proteolysis peptide maps and are immunologically cross-reactive. During adaptation to NaCl, unadapted cells synthesize and accumulate a major 26-kilodalton polypeptide, and the beginning of synthesis corresponds to the period of osmotic adjustment and culture growth. From our results, we suggest an involvement of the 26-kilodalton polypeptide in the adaptation of cultured tobacco cells to NaCl and water stress.

Purification and characterization of rat kidney L-alanine: 4,5-dioxovalerate transaminase and inhibition by hemin

Rat kidney L-alanine:4,5-dioxovalerate transaminase (EC 2.6.1.43), which may be involved in the formation of aminolevulinic acid in mammalian cells, was purified 82-fold to apparent homogeneity with a 19% yield. Molecular weight of the enzyme, as estimated by gel filtration, was found to be 225 000. In polyacrylamide gel electrophoresis under denaturing conditions, the enzyme moved as a single band corresponding to an Mr of 37 000, suggesting that the enzyme is composed of six identical subunits. The Km values of L-alanine and 4,5-dioxovalerate are 2.9 and 0.25 mM, respectively. The enzyme had an optimum activity at pH 6.6 and was most active at 65 degrees C. Among some amino acids tested, L-alanine proved to be the most efficient amino donor, and the enzyme was also stereospecific for the L-isomer. The effect of intermediate metabolites of heme biosynthesis, for example, delta-aminolevulinic acid, protoporphyrin, hemin and bilirubin has been studied on purified L-alanine:4,5-dioxovalerate transaminase. Amongst these metabolites, hemin and protoporphyrin were found to be effective inhibitors.