Variation in the degree of branching of the glycogens and an approximate relationship between average exterior chain length and iodine staining

The chemical structure of amylose and amylopectin fractions of starch from tobacco leaves during development and diurnally-nocturnally

Starches, isolated from rapidly expanding tobacco leaves four times during the day and night and once from fully expanded leaves, were fractionated with concanavalin A. From an examination of the amounts and properties of amylose, the diurnal decrease in iodine absorption of the starches on illumination appeared to be due to an increase in its branched character, and possibly the presence of unbranched polymer of low dp, combined with a decrease in the proportion of amylose fraction. The increase in apparent amylose content with age was due to an increase in the proportion of amylose. The amylose fractions at different times had only small differences in average mol size in solution and relative mol wt (M(r) near 4 x 10(5)) which were lower than those of storage organs. The average mol size in solution and relative mol wt of the amylopectins decreased during illumination, increased in darkness, and were lower (M(r) 2-2.7 x 10(6)) at all times than those from storage organs. Debranching followed by size-exclusion chromatography [on Fractogel TSK 50(S)] gave similar proportions of long, medium, and short chains for all amylopectin samples, and these proportions differed from those for debranched amylopectin from n-maize seed starch. On debranching and chromatography of the amylopectin beta-limit dextrins (which gives an estimate of the proportions of core chains) differences persisted. Structural characteristics of amylopectin from tobacco leaf starch were similar to those of normal genotypes from storage organs. The proportion of glucosyl units in core chains, the external-to-core chain ratio, and indices of compactness were calculated for a number of (1-->4)(1-->6) alpha-glucans. A plot of the index of compactness for glycogens and amylopectins showed that the decrease in compactness and the increase in total average chain length that occurs from glycogen to normal and then to amylose extender amylopectins involves a proportionate increase in average internal, external, and core chain lengths and not a selective increase in one type of chain.

A micromethod for the enzymatic estimation of the degree of glycogen ramification

A comparison of methods for the evaluation of glycogen content in liver tissue of rats has been carried out by determining the recoveries in the differential ethanol precipitation of glycogen from alkaline tissue digests as well as the actual quantitative equivalence between glycogen content and actual glucose measured. Hydrolytic/enzymatic methods gave lower results than non-specific chemical methods such as anthrone. These lower values, combined with the losses in the purification process resulted in much lower glycogen estimations than the actual estimated tissue content. A method has been devised for the measurement of glycogen ramification in small liver tissue samples, using neutral periodate oxidation of the molecule, followed by determination of the formic acid evolved from the branch ends with formic acid dehydrogenase. The method gave results very similar to the classical methods in which the acid formed is measured titrimetrically. Rat liver tissue contained a mean 323 +/- 69 mmol of glucose equivalents of glycogen per gram of tissue; this glycogen had a mean chain length of 11.4 +/- 0.8 units.

Chemical aspects of glycogen contrast-staining by potassium osmate

To obtain contrast-staining of glycogen in electron microscopy, various contrast-enhancing additives can be used in combination with potassium osmate. Examples are potassium ferrocyanide and certain nitrogen heterocyclic compounds, such as triazoles. In the reaction sequence leading to contrast-stained glycogen, a primary reaction is the formation of glycogen osmate. This reaction was studied with isolated glycogen. On the basis of the stoichiometric findings, a molecular structure of the reaction product is proposed; apparently, osmate is bound by glycogen because of the presence of suitably located hydroxyl groups. The resulting compound is not itself sufficiently electron dense, but it binds 1,2,4-triazole as an additional ligand. Secondary reactions can result in additional osmium binding, and finally to osmium (IV) deposits, leading to contrast.

A potentiometric method for the determination of the iodine-binding capacity of glycogen

The experimental conditions in the potentiometric method for the determination of the iodine-binding capacity (Ib) of starch and amylose [R. L. Bates, D. French, and R. E. Rundle (1943) J. Amer. Chem. Soc. 65, 142-148] were not suitable for glycogen because of the much lower affinity for iodine of the latter. This difficulty was overcome by titration of small volume with both the iodine and glycogen at high concentration. Using the concentration cell circuit Pt electrode-blank-bridge-glycogen-Pt electrode, small increments of standard iodine solution were added to the blank solution and each was titrated to null by adding iodine to the glucogen solution [G. A. Gilbert and J. V. R. Marriott (1948) Trans. Faraday Soc. 44, 84-93]. Glycogen was determined by an anthrone-sulfuric acid method [F. W. Fales (1951) J. Biol. Chem. 193, 113-124]. Glycogens with Ib's ranging from 1.8 to 5.3% were observed.