Nomenklatur und einige Eigenschaften der Molkenproteine. 2. Mitt. a-Lactalbumin, Immunoglobuline, Proteose-Peptone, Minorproteine und Enzyme' T. SIENKIEWICZ Die Struktur und Funktion von r-Lactalbumin und von anderen Molkenproteinen werden diskutiert und einige Aspekte der thermischen Proteindenaturierung beschrieben. a-Lactaibamia AIIgemeines und Primarstruktur(ca. 1.3 g/l) ist das a-Lactalbumin (a-La) das nveitwichtigste Molkenprotein der Kuhmilch. Unter den Molkenproteinen der Humanmilch ist das a-La dem Gehalt nach (4,6 g/l) das bedeutendste Protein. Zur Reindarstellung von a-La konnen Fallungsverfahren [S. 841 oder physikalische Trennmethoden [45, 1091 eingesetzt werden. Fur einige Verwendungszwecke reicht es aus, ,,robes" I-La-Praparat durch Ammoniumsulfatdllung zu gewinnen und von Blutserumalbumin durch die Gelfiltration an Sephadex G-75 oder G-100 abzutrennen. Besonders reines Praparat (ohne Minorkomponenten) ist durch anschlieknde Ionenaustauschchromatographie an DEAE-Cellulose (bzw. DEAE-Sephadex) zu gewinnen 1591. Die Bezeichnung a-La wurde im Jahre 1930 von S J~R E N und SVEDBERG eingefuhrt fur das erste (a) in der Ultrazentrifuge sedimentierendes Protein aus der durch Auskristallisieren aus lMolke gewomnen Albuminfraktion. Das a-La ist durch die Sgttigung der Molke mit Magnesiumsulfat nicht Gllbar. Die vollstandige Aminosiiuresequenz von a-La wurde von BREW u. a. [25] aufgeklgrt. Das in der Kuhmilch auftretende monomere Protein mit einer relativen Molekiilmasse von 14 176 besteht aus 123 Aminosiiuren und besitzt vier Cystin-und keine Cysteinreste. Weitere charakteristische Merkmale sind: Gesamtstickstoffgehalt von 15.86 %, der hochste Tryptophangehalt von allen bekannten natiirlichen Proteinen (6,9 g/100 g Protein) und ein hohes Verhaltnis von polaren zu nichtpolaren Aminosauren. Der Gehalt von essentiellen Aminosauren ist hoch. der prozentuelle Absorbtionskoeffizient A: : ': bei 280 nm Wellenlange des UV-Lichtes 20.1 bzw. 20,6 [70, IOO]. Gegenwartig ist r-La bei 13 Tierarten gefunden, isoliert und charakterisiert worden [MI. Von Rinder-a-La 1261, Human-a-La [44] und Meerschweinchen-@-La [23j sind die vollstandigen Aminosiiuresequenzen bekannt. Teilsequenzen wurden von vier weiteren a-La ermittelt 1641. z-La kommt in allen Milcharten, die Lactose enthalten, vor. Am Beispiel von 6 Tierarten zeigten LEY u. a. [75], daD zwischen a h -und Lactosegehalt eine positive Korrelation besteht. Dies ist nicht iiberraschend, seitdem bekannt ist, daO das a-La das ,,B"-Protein eines Enzyms ist, niimlich der Lactose-Synthetase [40], Mit einem Gehalt bis zu 25 I. Mitt. Nahrung, 25, 329 (1981).

No abstract

Early reports on linseed proteins are mostly concerned with solubilization of total proteins from oil-free meal by different solvents and their isolation [6, 81, paper electrophoretic characterization and amino acid composition [7]. Classification of proteins in defatted linseed meal, based on their solubilities in various solvents, has shown the salt-soluble protein to be a major fraction in linseed [3, 91. Employing different physicochemical techniques, it has been demonstrated that total proteins of linseed consist of at least 3 components of which the major one, apparently, is a high molecular weight globulin [Z, 41. MADHUSUDHAN et al. [5] isolated the major fraction of linseed proteins and reported its physicochemical characteristics. Here, we report the isolation of linseed globulin by a different procedure and its characterization by sodium dodecyl sulphate -polyacrylamide gel electrophoresis (SDS-PAGE) and sedimentation analysis. Material and methodsSeeds, purchased locally, were milled and defatted by repeated extractions, alternately, with diethyl ether and acetone at 4 C . Total proteins were extracted from the oil-free meal, following desolventization at room temperature and passing through a 0.25 mm screen, with phosphate buffer containing I .O M NaCl using meal :solvent ratio of 1 : 20. The clear extract, obtained by repeated centrifugations (3000 x g for I5 min) at 20 C, was diluted with 5.5 times its volume ofdistilled water and kept at 4 'C for several hours. The cryoprecipitated globulin was separated by centrifuging at 4 C and dissolved in a small volume of the extractant. The process of precipitation and centrifugation was repeated twice. Finally, the isolated protein was dissolved in the extractant buffer to which sodium azide was added at a concentration of 0.02"/,. This sample was called "crude globulin".The crude globulin fraction was eluted through a Sephadex (3-200 column using phosphate buffer as described elsewhere (21. The ultraviolet absorption spectrum of the eluate at 280 nm showed a peak with a prominent shoulder. The eluate fraction corresponding to the peak were pooled. concentrated by ultrafiltration using a PM-10 membrane with a cut-off limit of 10000 daltons and rechromatographed to obtain a somewhat symmetric peak. The eluate volume under this peak was diluted in the ratio 3 : 5 with distilled water and concentrated 10-fold by ultrafiltration using the same membrane. This was referred to as "purified globulin".Electrophoresis was carried out on 8.79< polyacrylamide disc gels ( 5 x 0.5 cm. length x diameter) using 0.5 "6 SDS -0.05 M Tris-glycine (pH 8.3) buffer system [2]. The relative intensity of the stained bands on polyacrylamide gel was determined by scanning the cylindrical gels with a Hitachi dual wavelength chromatoscanner. Peak areas were determined by integration from the densitometric scans of the PAGE gels and the relative proportions of the major subunits were calculated.The sedimentation coefficient (s;,,,) of purified globulin was determined according to BEHL...

In einer Übersicht werden gemeinsame Merkmale der Molkenproteine dargestellt. Die Struktur und die Funktion von β‐Lactoglobulin sowie einige Aspekte der thermischen Proteindenaturierung werden beschrieben.

Unlike most other oilseed proteins, proteins from flaxseed have not been extensively studied. Nitrogen solubility of defatted flaxseed meal has been variously investigated [ I . 3 -51. Amino-acid compositions of oil-free meal and isolated proteins from flaxseed have also been reported (2. 3, 61. MADHUSUDHAN et al. [I J recently characterized total proteins of flaxseed by gel filtration. ion-exchange chromatography, elcctrophoresis and ultracentrifugation, and reported the presence of at least 3 components. To obtain further inforination on flaxseed proteins, we performed the fdllowing experiments.A defatted tlour (DF. particle size <250 pm) obtained from cold-pressed flaxseed meal. a protein isolate ( P I ) prepared by alkaline extraction (NaOH, pH 9.5) and isoelectric precipitation (HCI. pH 4.2) of proteins, and two water-and salt-soluble protein fractions (WSPF and SSPF) obtained by successive extractions of D F with C0,-free distilled water and 0.5 M NaCl, respectively, followed by dialysis against distilled water at 4 'C for 48 h, were studied for their gel electrophoretic pn&rns and amino-acid profiles. The protein preparations were freeze-dried before the studies.