Glucose with peptides

Insulin Secretion. Basal or stimulated (by glucagon or glucose) C-peptide concentrations can provide an estimate of a patienfs insulin secretory capacity and rate. For example, diabetic patients with C-peptide concentrations greater than 1.8 tg/L (1.8ng/mL) after stimulation with glucagon behave clinically like patients with type 2 diabetes, and those with low peak C-peptide values (less than... 

As with peptide hydrolysis, several enzyme systems exist that catalyze carboxylic and phosphoric ester hydrolysis without the need for a metal ion. They generally involve a serine residue as the nucleophile in turn, serine may be activated by hydrogen-bond formation—or even proton abstraction—by other acid-base groups in the active site. The reaction proceeds to form an acyl- or phosphory 1-enzyme intermediate, which is then hydrolyzed with readdition of a proton to the serine oxygen. Mechanisms of this type have been proposed for chymotrypsin. In glucose-6-phosphatase the nucleophile has been proposed to be a histidine residue. ... 

Furthermore, the gate area of pH-sensitive ISFET s (ion-sensitive field-effect transistor) has been covered with pH changing enzymes, such as urease and )8-lactamase [12]. Furthermore, ATPase, glucose oxidase, and trypsin were used for ATP, glucose, and peptide ENFET s (enzyme-field-effect transistor). 

During Strecker degradation of [l-i CJ-D-glucose with primary a-amino acids, pyrroles and pyridinols are formed as major products (6). 4-Aminobutyric acid and peptide bound lysine are transformed into [i3CHO]-2-formyl-5-hydroxymethylpyrroles (9). Amino acids like Val, He, Leu, Phe and Met are transformed into 2-[i3cjjO]-pyrrole lactones (70). Equimolar amounts of cysteine (methionine) and [l(or 6)- C]-D-glucose were heated for 1,5 h at 160°C in aqueous solution at pH 5. The volatiles were extracted with pentane/ether and analyzed as described (7). In Table I selected (unlabeled) Strecker degradation products from cysteine and methionine are summarized. Pyruvat (1), 2- and 3-mercaptopropionic acids (2, 3) from cysteine as well as 2-oxo-5-thiahexanoic acid (4) and 5-thiahexanoic acid (5) from methionine. 

Table 2. TBA value and chemiluminescent intensity (CL) of liver homogenate of rats fed with peptide-glucose reaction product and soybean paste...

Amadori reaction. - The 1-amino-1-deoxy-D-fructose derivative 5 was synthesized by condensation of D-glucose with hippuryl-lysine in methanol it was intended for use as a standard in the analysis of protein-fhictosamines by reaction with nitro blue tetrazolinium (NBT) undo alkaline conditions, but it and related peptide-fructosamines gave much lower relative responses than the protein-fructosamines in this assay. ... 

To illustrate this, imagine that we are comparing the absorption of glucose with a small peptide. If we measure mass transfer at the same infusion rate (i.e., at equal intestinal flow), we will usually find different unstirred layer thicknesses. There are several reasons why this could occur. First, while glucose is controlled by uptake in the intestinal lumen, peptide uptake may be controlled by transport across the intestinal wall. Even if mass transfer of both solutes is controlled by rates in the lumen, the mass transfer coefficient rarely depends linearly on the diffusion coefficient D. A more typical dependence is on the square root of D. If this is so, then the unstirred layer thickness I depends on D, which makes little sense physically. 

Nicotinic acid is found in plants associated with both peptides and polysaccharides. For example in wheat bran, two forms are described a peptide with a molecular weight of approximately 12,000 and a carbohydrate complex that is called niacytin. Polysaccharides isolated from wheat bran have been found to contain 1.05% nicotinic acid in bound form. Hydrolysis yielded a fragment identified as P-3-O-nicotinoyl-D-glucose (25). 

---