The N-terminal amino acid sequence of the beta-subunit of the legumin-like protein from seeds of Ginkgo biloba

The sequence of the first 52 amino acids at the N-terminus of the beta-subunit of a legumin-like protein from seeds of the gymnosperm Ginkgo biloba were determined by automated sequencing and DABITC/PITC microsequence analyses of peptides derived from the protein by enzymatic digestions and chemical cleavage with CNBr. The protein from Ginkgo exhibits sequence homologies (32-49% identities) with the 11S globulins and legume-like proteins from seeds of various angiosperm monocotyledons and dicotyledons.

A protease responsible for post-translational cleavage of a conserved Asn-Gly linkage in glycinin, the major seed storage protein of soybean

The assembly of 11S globulin seed storage proteins in plants is regulated in part by the activity of a protease that cleaves between asparagine and glycine residues. Post-translational cleavage of subunit precursors into acidic and basic polypeptides is associated with the ability of subunits in trimers to aggregate into hexamers in vitro. An activity is present in extracts from immature soybean seeds that specifically cleaves immature 11S seed storage proteins of soybean and Vicia faba into the polypeptides of the mature proteins. Sequence microanalysis has been used to demonstrate that proglycinin and prolegumin are cut at the legitimate site when proteins synthesized in vitro are used as substrates. A single amino acid change in the cleavage site renders the substrate uncleavable. The protease responsible for this activity also hydrolyzes a synthetic octapeptide whose sequence reproduces four amino acids on either side of the glycinin subunit G4 cleavage site. This assay permitted the purification and characterization of the protease. It is a glycosylated enzyme with an acidic pH optimum and a molecular mass of about 45 kDa in solution.

Soybean protein solubility in potassium hydroxide: an in vitro test of in vivo protein quality

Experiments were conducted to assess protein solubility in .2% KOH as an indicator of soybean protein quality for chicks and pigs and to assess effects of particle size on protein solubility. As the particle size (micron) of soybean meal (SBM) increased, protein solubility (%) decreased (b = -.0206). In two 9-d chick trials, dehulled SBM (48% CP) was subjected to various autoclaving times and then fed as the sole source of dietary protein to young chicks. Increasing autoclaving times from 0 to 40 min at 120 degrees C resulted in a quadratic decrease in protein solubility. A broken-line model was fitted wherein gain:feed of chicks was plotted as a function of protein solubility. The analysis showed no reduction in feed efficiency with solubilities greater than 59 +/- 1.5% (mean +/- SEM). When solubility was below 59%, however, gain:feed decreased 1.5% for each 1% decrease in protein solubility. The third trial (13 d) was conducted with 7.5-kg pigs fed autoclaved SBM (44% CP) as the primary source of protein. Feed efficiency was significantly decreased when protein solubility was less than 66%. This study showed that protein solubility in KOH was a good index of in vivo soybean protein quality, and that it is important to standardize SBM particle size when applying the KOH assay.

Changes in the nutritive value of soy protein concentrate during autoclaving

Soy protein concentrate (Promosoy R Plus) was mixed with water to form a thick paste and autoclaved at 121 degrees C for 10 min, 30 min, 2 h, or 4 h. Unautoclaved SPC served as a control. Nitrogen solubility measurements and SDS-PAGE analysis indicated that autoclaving resulted in the formation of soy protein aggregates, with a MW of approximately 1 million daltons, held together by non-covalent and disulfide bonds. The 10 min, 30 min, 2 h, and 4 h SPC samples contained 6, 20, 27 and 39% less cysteine, respectively, than the SPC control. No significant differences were found in the PERs, 2.6-2-7, of a casein control, unautoclaved SPC control and 10 min and 30 min autoclaved samples. PERs of the 2 h and 4 h autoclaved samples, 2.0 and 1.9 respectively, were significantly lower than the other four diets. No significant differences were found in the apparent digestibility of the 10 min, 30 min, and 2 h autoclaved samples; the 4 h autoclaved sample however was significantly less digestible. Decreased PERs of autoclaved SPC samples were likely due to (1) crysteine destruction, (2) decreased protein digestibility, and (3) decreased food intake.

Water vapor adsorption and desorption isotherms of biologically active proteins

Using a protein isolated from soy, a dynamic water adsorption method was developed and the data were compared with those obtained from a static gravimetric procedure. Both methods gave comparable results, showing that Type II isotherms with considerable hysteresis were obtained. However, the dynamic procedure was preferred since it provided data rapidly and used significantly less material. Using the dynamic method, water adsorption isotherms at 25 degrees C were also determined for four biologically active proteins: alpha-amylase, beta-glucuronidase, lipase, and urease. BET (Brunauer, Emmet, and Teller) parameters were calculated and the specific surface areas for the native, biologically active proteins were found to be similar, 238.4 +/- 20.2 m2/g. On the other hand, the specific surface area for the denatured soy protein isolate was 144.6 m2/g. Nevertheless, the heat of absorbance for all of the proteins examined was similar, suggesting that they have comparable degrees of hydrophilicity.

Relationship between the limited proteolysis of glycinin and its conformation

The relationship between the limited proteolysis and conformation of native glycinin was studied by the following methods: analyses of the proteolytic digestion of chemically modified glycinin, circular dichroism (CD) measurements, a secondary structure prediction from the amino acid sequence and a hydropathy index analysis. The locations of tryptic fragments of glycinin were confirmed from the N-terminal amino acid sequences of the fragments. T fragments and P fragments were located at the N-terminal and central area of the acidic polypeptide chains, respectively. One of the cleavage sites was the Arg residue of around the 100th from the N-terminal side. The regions digested by limited trypsinolysis were presumed to be flexible, hydrophilic and near the surface of the molecule by prediction methods from the amino acid sequence. The other regions were predicted to be compact and beta-sheet in nature, almost 40-50% of the amino acid residues being predicted as beta-sheet from the amino acid sequence and from CD data.

Purification and characterization of ornithine transcarbamylase from pea (Pisum sativum L.)

Pea (Pisum sativum) ornithine transcarbamylase (OTC) was purified to homogeneity from leaf homogenates in a single-step procedure, using delta-N-(phosphonacetyl)-L-ornithine-Sepharose 6B affinity chromatography. The 1581-fold purified OTC enzyme exhibited a specific activity of 139 micromoles citrulline per minute per milligram of protein at 37 degrees C, pH 8.5. Pea OTC represents approximately 0.05% of the total soluble protein in the leaf. The molecular weight of the native enzyme was approximately 108,200, as estimated by Sephacryl S-200 gel filtration chromatography. The purified protein ran as a single molecular weight band of 36,500 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These results suggest that the pea OTC is a trimer of identical subunits. The overall amino acid composition of pea OTC is similar to that found in other eukaryotic and prokaryotic OTCs, but the number of arginine residues is approximately twofold higher. The increased number of arginine residues probably accounts for the observed isoelectric point of 7.6 for the pea enzyme, which is considerably more basic than isoelectric point values that have been reported for other OTCs.

Changes of the oligomeric structure of legumin from pea (Pisum sativum L.) after succinylation

The influence of various levels of succinylation on the structure of the legumin from pea seed has been studied by the techniques of sedimentation velocity, viscometry, fluorescence and circular dichroism spectroscopy, as well as dynamic light scattering. The protein dissociates gradually into the 3S subunit forming a 7S intermediate. At a level of 75-80% succinylation, sudden unfolding of the protein occurs characterized by drastic changes in viscometric and spectroscopic properties. The fluorescence spectra point to the formation of a novel organized structure at a moderate degree of modification before the molecular unfolding takes place. The succinylated subunit was shown to have a sedimentation coefficient of 3.2S, a diffusion coefficient of 5.03 x 10(-7) cm2 . s-1 a Stokes' radius of 4.24 nm, a partial specific volume of 0.703 ml/g, an intrinsic viscosity of 0.13 dl/g, a molar mass of 52.2 kDa and a frictional ratio of 1.74.

Improvement of nutritional value and functional properties of soybean glycinin by protein engineering

Glycinin is one of the predominant storage proteins of soybean. To improve its functional properties (heat-induced gelation and emulsification) and/or nutritional value, the A1aB1b proglycinin subunit was modified on the basis of genetically variable domains suggested from the comparison of amino acid sequences of glycinin-type globulins from various legumes and nonlegumes and the relationships between the structure and the functional properties of glycinin. Thus, nucleotide sequences corresponding to each of the variable domains were deleted from the cDNA encoding the A1aB1b proglycinin, and a synthetic DNA encoding four continuous methionines was inserted into the cDNA region corresponding to each of the variable domains. Expression plasmids carrying the modified cDNAs were constructed and expressed in Escherichia coli strain JM105. Some of the modified proteins were accumulated as soluble proteins in the cells at a high level and self-assembled. They exhibited functional properties superior to those of the native glycinin from soybean, which establishes the possibility of creating theoretically designed novel glycinins with high food qualities.

Association and folding in legumin oligomers of lupin seed

We studied the association and conformational behavior under native or denaturing conditions in the 12S in equilibrium with 7S oligomers of lupin legumin and in the modified 7S (m7S) oligomer, which has lost the capacity to make a 12S molecule. Circular dichroism (CD), gel filtration FPLC, and PAGE were used. The native m7S oligomer has more alpha helix and nearly the same amount of beta structure as the 12S in equilibrium with 7S preparation. Conditions that shift the equilibrium in the 12S in equilibrium with 7S system toward the 7S oligomer also make the secondary structure more similar to that of m7S molecules: higher negative ellipticity appears to be a peculiarity of 7S assemblies, whether they contain modified or unmodified monomers. Part of the helical components show low stability and disappear in 1 M urea. The CD and the separation behavior on increasing the urea concentration, and in 6 M guanidine HCl, denote similar multistep unfolding in both preparations. The 12S oligomer disassembles progressively: however, also under highly denaturing conditions, modified and unmodified preparations are mainly present in an associated form. Small amounts of monomer and aggregates were detected at high denaturant concentrations.

[The use of monoclonal antibodies against insulin for isolation of proteins inhibiting the cell growth]

Extracts of pig kidneys or germinated soya beans after preliminary steps were affinity chromatographied on Sepharose containing cyanogen bromide immobilized monoclonal antibodies to pig insulin. The material bound to the affinity column was separated by HPLC resulting in one homogeneous protein from each source. Both proteins have been shown to inhibit DNA synthesis in cultured embryonic human fibroblasts and VERO fibroblasts. The effect of pig kidney protein was potentiated by insulin. Soya and pig proteins were characterized by the following parameters: molecular weights of 8.5 and 10.3 kD, apparent constants of dissociation with rat liver plasma membranes of 4.7 x 10(-8) M and 9.8 X 10(-8) M, respectively. The soya proteins competed for the binding sites on plasma membranes with insulin whereas the pig protein did not. The N-terminal amino acid sequences of 20 residues were determined for both proteins. Comparison of these sequences with known protein sequences was performed. A 30-40% primary structure homology of the studied fragment of soya bean protein with the fragments of some oncogenic viruses proteins and transforming proteins was revealed.

Characterization and distribution of a maize cDNA encoding a peptide similar to the catalytic region of second messenger dependent protein kinases

Maize (Zea mays) roots respond to a variety of environmental stimuli which are perceived by a specialized group of cells, the root cap. We are studying the transduction of extracellular signals by roots, particularly the role of protein kinases. Protein phosphorylation by kinases is an important step in many eukaryotic signal transduction pathways. As a first phase of this research we have isolated a cDNA encoding a maize protein similar to fungal and animal protein kinases known to be involved in the transduction of extracellular signals. The deduced sequence of this cDNA encodes a polypeptide containing amino acids corresponding to 33 out of 34 invariant or nearly invariant sequence features characteristic of protein kinase catalytic domains. The maize cDNA gene product is more closely related to the branch of serine/threonine protein kinase catalytic domains composed of the cyclic-nucleotide- and calcium-phospholipid-dependent subfamilies than to other protein kinases. Sequence identity is 35% or more between the deduced maize polypeptide and all members of this branch. The high structural similarity strongly suggests that catalytic activity of the encoded maize protein kinase may be regulated by second messengers, like that of all members of this branch whose regulation has been characterized. Northern hybridization with the maize cDNA clone shows a single 2400 base transcript at roughly similar levels in maize coleoptiles, root meristems, and the zone of root elongation, but the transcript is less abundant in mature leaves. In situ hybridization confirms the presence of the transcript in all regions of primary maize root tissue.

Heat-induced reversible gelation of arachin: kinetics, thermodynamics and protein species involved in the process

Arachin forms a heat-reversible gel under certain experimental conditions. The minimal gelling concentration for this system is 7.25%. Above minimal gelling concentration calculation of thermodynamic parameters for gelation of arachin revealed a constant delta Hbonding (-1220 cal.mol-1) where delta Sbonding values varied with an increase in protein concentration (ranging from -4.01 e.u. at 7.5% to -3.48 e.u. at 10.0%). The main steps involved in the gelation phenomenon include thermal denaturation of arachin, partial aggregation of heat-denatured protein molecules, setting of protein solution and maturation of the gel formed. Gel maturation process follows first order kinetics and is characterized by a large positive delta G+(+) (22,030 cal.mol-1). Determination of delta H+(+) and delta S+(+) for this process revealed that mostly delta S+(+) (-62.9 e.u.) contributes to the large positive delta G+(+), thus decreasing the overall rate of gel maturation process. This large negative delta S+(+) value probably arises from a loss of entropy of protein molecules because of their increased involvement in gel network formation. The polymer gel network seems to be primarily contributed by a part of both arachin dodecameric and hexameric species.

Mass balances for a biological life support system simulation model

Design decisions to aid the development of future space-based biological life support systems (BLSS) can be made with simulation models. Here we develop the biochemical stoichiometry for 1) protein, carbohydrate, fat, fiber, and lignin production in the edible and inedible parts of plants; 2) food consumption and production of organic solids in urine, feces, and wash water by the humans; and 3) operation of the waste processor. Flux values for all components are derived for a steady-state system with wheat as the sole food source. The large-scale dynamics of a materially-closed (BLSS) computer model is described in a companion paper. An extension of this methodology can explore multi-food systems and more complex biochemical dynamics while maintaining whole-system closure as a focus.