Analysis of some partly and fully esterified oligogalactopyranuronic acids by p.m.r. spectrometry at 220 MHz

The p.m.r. spectra of mono-, di-, tri-, tetra-, and penta-galactopyranuronic acids (1–5), the corresponding fully esterified methyl esters (6–10), the partly esterified di- (11) and tri-galactopyranuronic acids (12, 13), and the unsaturated di-, tri-, and tetra-galactopyranuronic acids (14–16) were measured on solutions in D₂O at 220 MHz at a pH of 1 and 6. Observation of doublets (J 4 Hz) in the range δ 4.90–5.05 p.p.m. indicates the site of esterification in the non-reducing or reducing sugar residue. Esterification of the sugar residue at the non-reducing end can be deduced from both the presence of a methyl resonance peak at δ 3.80 and the indifference of the signal at δ 4.35 (H-4) to the change in pH. The δ values and coupling constants confirm that all the d-galacturonic acid residues have the CI conformation and are α-(1→4)-linked. In the unsaturated oligogalactopyranuronic acids, the double bond is located between C-4 and C-5 of the sugar unit at the non-reducing end. The 4-deoxyhex-4-enopyranosyluronic acid residue occurs in the ²H₁(d) conformation. Compound 11 was identified as O-(α-d-galactopyranosyluronic acid)-(1→4)-(methyl α,β-d-galactopyranuronate). Compounds 12 and 13 each consisted of a mixture of the three possible isomers; preference for the site of esterification decreases in the order reducing sugar unit, non-reducing sugar unit, sugar unit at the non-reducing end.     

Enzymatic hydrolysis of beer brewers' spent grain and the influence of pretreatments

The enzymatic saccharification of plant material has been shown to be of interest in various fields, such as the production of fruit juices(1,2) and the utilization of biomass.(3) A combination of cellulase, pectinase, and hemicellulases is usually used because of the chemical composition of the matrix of plant cell walls.For apples, beet pulp, and potato fiber, almost a complete hydrolysis of polysaccharides is obtained by combining cellulose and pectinase. For nonparenchymatic tissue, the situation is somewhat different: pectin is a minor component and the hemicellulose content is much higher. Enzyme action is restricted by the lignin barrier and by the high crystallianity of cellulose in this material. For such materials, mechanical, thermal, or chemical pretreatments are necessary to achieve hydrolysis.(4,5)This communication describes various enzymatic treatements and chemical and physical pretreatemtn, using brewers' spent grain as substrate. Spent grain is the residue of malt and grain which remains in the mash-kettle after the liquefied and saccharified starch has been removed by filtration.     

Nucleotide sequence analysis of the lemur beta-globin gene family: evidence for major rate fluctuations in globin polypeptide evolution

Lemur beta-related globin genes have been isolated and sequenced. Orthology of prosimian and human epsilon-, gamma-, and beta-related globin genes was established by dot-matrix analysis. All of these lemur globin genes potentially encode functional beta-related globin polypeptides, though precisely when the gamma-globin gene is expressed remains unknown. The organization of the 18-kb brown lemur beta-globin gene cluster (5' epsilon-gamma-[psi eta-delta]-beta 3') is consistent with its evolution by contraction via unequal crossing-over from the putative ancestral mammalian beta-globin gene cluster (5' epsilon-gamma- eta-delta-beta 3'). The dwarf lemur nonadult globin genes are arranged as in the brown lemur. Similar levels of synonymous (silent) nucleotide substitutions and noncoding DNA sequence differences have accumulated between species in all of these genes, suggesting a uniform rate of noncoding DNA divergence throughout primate beta-globin gene clusters. These differences are comparable with those observed in the nonfunctional psi eta pseudogene and have therefore accumulated at the presumably maximal neutral rate. In contrast, nonsynonymous (replacement) nucleotide substitutions show a significant heterogeneity in distribution for both the same gene in different lineages and different genes in the same lineage. These major fluctuations in replacement but not silent substitution rates cannot be attributed to changes in mutation rate, suggesting that changes in the rate of globin polypeptide evolution in primates is not governed solely by variable mutation rates.      

Distribution of methoxyl groups in apple pectic substances

The distribution of methoxyl groups in apple pectic substances was investigated by means of fractionation on ion-exchange and gel-filtration columns and by means of degradation of pectin fractions by pectin lyase and pectate lyase. Pectin fragments thus obtained were fractionated by gel-permeation chromatography and high-pressure liquid chromatography. It was concluded that a heterogeneous intermolecular distribution of the methoxyl groups exists with peaks at degrees of esterification of about 50%, 70% and 95%. The intramolecular distribution of the methoxyl groups cannot be distinguished from a random distribution. Since plant pectin esterases cause a blockwise de-esterification, it is unlikely that the biosynthesis of apple pectic substances passes through a stage of 100% esterification after which partial de-esterification by pectin esterase occurs.     

Comparison of the structural features of apple and citrus pectic substances

Pectic substances were extracted from Alcohol Insoluble Solids from lemon peel (albedo) and fractionated by ion exchange chromatography and gelfiltration. The pectin molecules contained rhamnose, arabinose, galactose, glucose and galacturonic acid residues; xylose residues were almost absent. Degradation with purified pectolytic enzymes and subsequent gelfiltration of the resulting pectin fragments showed that the neutral sugar side chains were present in ‘hairy regions’ (blocks of neutral sugar side chains). The distribution of the methoxyl groups was studied by HPLC analysis of enzyme-degraded pectins. Some influence of native pectinesterase on the distribution of the methoxyl groups was found. The results are compared with those of similarly extracted and purified apple pectic substances.