Maltose labeled

Initially, attempts to grow the organism on sodium acetate as the sole source of carbon were unsuccessful, but the difficulties were overcome and mannitol, arabinitol, erythritol, glycerol, maltose, and a,a-trehalose were produced. This was a useful development because conditions were established for the incorporation of [14C] acetate, thereby making labeled polyols and disaccharides available. 

Configurational dependence of lJc-, c-v> values has been observed with acetates of [l -13C]-labelled cellobiose, laminarabiose, maltose, and nigerose, the a- and /3-linked disaccharides respectively giving29 the values of 46.5 and 49.2 Hz. 

Figure 1. Schematic representation of two contiguous a-(1-4) linked glucopyranose residues (maltose), along with the labelling of the atoms and the torsion angles of interest.

On the radioautogram of the hydrolytic products initially produced from the tetrasaccharide, the maltotriose was labeled, but the glucose was not. As the concentration of the maltotriose increased in the incubation mixture, a hydrolysis of the trisaccharide occurred to yield labeled maltose and non-labeled glucose. On prolonged incubation the tetrasaccharide was completely converted to glucose by the glucoamylase. 

Mundt el al.n9 have adapted the above scheme for the maltose-glycine system (pH 5.5, 70 °C). Multiresponse modelling gave excellent fits for the time course of the concentrations of glucose, melanoidins (A470, number of maltose molecules incorporated from U-14C-labelled maltose), 3-DH (as quinoxaline derivative), maltose, and SIV (in maltose-glycine-SIV systems). 

The entire pseudotetrasaccharide acarbose (16) derives from this obscure C7 sugar and three molecules of glucose [60]. There is evidence from incorporation experiments with labeled maltose and with derived from the fermentation medium [U- C3]glycerol that the rings C and D are attached as an intact maltose unit, i. e., as a disaccharide. This is an example, in which a tetrasaccharide is assembled in a more convergent fashion than the generally postulated linear stepwise formation (Scheme 20a). 

Fig. 1. H- - C CT-HSQC spectrum of a sample of 1.5mM Val, Leu, lie (51) methyl-protonated maltose-binding protein (MBP), 2mM /3-cyclodextrin, 20 mM sodium phosphate (pH 7.2), 3mM NaN(, 200pM EDTA, 0. 1 mg/ml Pefabloc, 1 /ig//d pepstatin and 10% D20 recorded at 37°C, on a Varian Unity-1- 500-MHz spectrometer. Acquisition times of 28 and 64 ms were employed (/, t2) along with a relaxation delay of 1.5 s, fora total measuring time of 3 h. (a) Aliphatic region of the H- - C correlation map of MBP, illustrating the selectivity of labelling. Small amounts of residual protonation are observed at the Cy positions of a number of Pro/Arg residues, the Cp positions of Asp and Ser (aliased) residues, and the Cy2 methyl positions of lie. In all cases, intensities of these cross-peaks are less than 10% of the methyl peaks, (b) Methyl region of the H- - C HSQC. Reproduced with permission from Kluwer Academic Publishers Goto et al.H...

The conventional mass spectra obtained from saccharides transformed into their OTMS and -OCH3 derivatives were interpreted by using labeled derivatives. Systematic studies had never been performed on -OAc derivatives. However, in 1975, Das and Thayumanavan [230] studied various peracetylated disaccharides by their IKE spectra to resolve the ambiguity appearing in the El mass spectra of the isomeric peracetates of trehalose, sophorose, kojibiose, laminaribiose, maltose, melibiose and gentiobiose, all characterized by the same molecular weights (678). 

At equilibrium, the ratio of maltose to D-glucose is 0.52. By use of substrates labeled with carbon-14, it was diown that the reducing group of the maltose molecule is liberated as free D-glucose, and the nonreducing residue is transferred to the donor substrate. In the presence of D-glucose oxidase, equilibrium is not established, and polysaccharide which is stained blue by iodine is synthesized. Amylomaltase thus superficially resembles D-enzyme, although it must be emphasized that maltose is not a substrate for D-enzyme, which transfers two or more hexose residues at a time. 

Labeling starch with the 14C isotope of carbon at the anomeric position of the reducing terminal D-glucose unit was achieved by treatment with labeled cyanide followed by alkaline hydrolysis of the resulting cyanohydrin.17 Labeled maltose could be prepared from such labeled starch.18 In addition, starches modified by substitution might be labeled in the substituent being introduced, as shown by Kratz and Kaufmann,19 who prepared starch acetylsalicylate with 14C in the acetylsalicylate moiety. 

---