Damage to proteins, enzymes, and amino acids by peroxidizing lipids.

Amino acid separation with 6 different solvents on chromatoplates prepared from Kieselgel G (‘Merck’) is described. As demonstrated in Figur 8 and discussed in the text, this technique is equal or superior to paper chromatography.

Dünnschicht-Chromatographie von Aminosäuren

Presence of alliinase in isolated vacuoles and of alkyl cysteine sulphoxides in the cytoplasm of bulbs of onion (Allium cepa)

β-Glucans in barley endosperm cell walls exist as polymers of very high molecular weight (about 4 × 107 daltons) containing firmly linked peptide sequences. This peptidic material is an essential part of the structure of the β-glucan complex as it exists in the cell wall. Rupture of peptide bonds by hydrazinolysis or with the proteolytic enzyme thermolysin gives β-glucans similar in size to those from short-grown green malts (about 106 daltons). This suggests that proteolysis is the first step in β-glucan degradation.

Large β-glucans are not all precipitated in 30% (w/v) ammonium sulphate; only 34% of the β-glucan in a hot aqueous extract of cell walls is precipitated. The amount is increased to 63% if the cell walls have been previously dehydrated.

Prolonged incubation of cell wall β-glucan at 40°C, mechanical stress, chromatography lasting 8–10 h at or above 65°C, or chromatography in M sodium chloride causes some disassociation of high molecular weight β-glucan to a size of about 107 daltons. Heating a solution for 1 h at 100°C does not disassociate the β-glucan.

Pentosans isolated from cell walls are not covalently linked to the β-glucans and can be separated from them by molecular sieve chromatography. They have a higher xylose/arabinose ratio than previously reported for barley pentosans. The pentosan molecules extracted by water are smaller (106 daltons) than those extracted by alkali (5 × 106 daltons).

Little difference was observed in the chemical or physical properties of cell wall materials of barley cultivars of different malting qualities.

THE MODE OF BINDING OF β-GLUCANS AND PENTOSANS IN BARLEY ENDOSPERM CELL WALLS

Free amino acids and peptides are markedly hydrophilic compounds, only slightly soluble in non-aqueous solvents. This must be borne in mind when sampling and preparing materials for TLC as well as when choosing the solvent. Some data on solubilities of a few amino acids in various solvents which illustrate this are:

Amino Acids and Derivatives

Polychromatic Technique for Identification of Amino Acids on Paper Chromatograms

The use of xylene rather than chloroform to extract the nickel(II)-4- isopropyl- l,2-cyclohexanedionedioxime chelate results in increased sensitivity in the spectrophotometrie determination of nickel. The extraction coefficient in xylene is more than five times as great as that in chloroform, and the low solubility of xylene in aqueous solution permits the use of much larger phase ratios (aqueous to organic). The system eonforms to Beer's law for concentrations of nickel from 1 to 12 of nickel per ml. of xylene. The precision of the method is 2%. Iron, cobalt, and copper interfere seriously; however, their interference can be minimized so that weight ratios of metal to nickel of 20, 2, and 8, respectively, can be tolerated. Concentrations of nickel from 0.005 to l00 ppm were determined in water, alkali metals, and several analytical reagents. Recoveries in excess of 95% were obtained when known amounts of nickel were extracted from aqueous solutions of relatively high ionic strength at aqueous-to-organic volume ratios as high as 300 to 1. (auth)

R. E. Feathers

Papers

Polychromatic Technique for Identification of Amino Acids on Paper Chromatograms

Spectrophotometric determination of traces of nickel with 4-isopropyl-1,2- cyclohexanedionedioxime