Dexter French

CHAPTER VII – ORGANIZATION OF STARCH GRANULES

Publisher Summary Starch granules range in size from sub-micron elongated granules of chloroplasts to the relatively huge oval granules of potato and canna. Semi-compound granules originate as two or more distinct granules, which then fuse together. Pseudo-compound granules, such as pea starch granules, start out as individual granules, which then develop several large cracks while remaining a single entity. These differences in size and shape make it possible to recognize most of the ordinary food and commercial starches. Starch granules contain small amounts of non-carbohydrate components—lipids, proteins, phosphate, and ash—that affect the behavior of starch in various applications. The tiny starch granules of chloroplasts are important as a temporary carbohydrate reserve and show diurnal synthesis and degradation. Native starch granules show growth rings when observed by optical microscopy, scanning electron microscopy of eroded granules, and transmission electron microscopy of thin sections, especially after chemical treatment. Starches that show prominent growth rings, such as potato starch, require high or saturating water levels for ring visibility.

The Reactions of Formaldehyde with Amino Acids and Proteins

Publisher Summary This chapter focuses on the reactions of formaldehyde with amino acids and proteins. Formaldehyde is a reagent familiar to all protein chemists through its employment in the formol titration of amino acids and peptides. Formaldehyde has been widely used as a tanning agent for collagen and other fibrous proteins. Like other such agents, it renders these proteins relatively inert to digestion with trypsin and greatly decreases their tendency to swell in water or in acid or alkaline solutions. All these properties of formaldehyde are of great interest, both theoretically and practically. Formaldehyde can combine with any one of a number of different kinds of functional groups found in proteins. When steric relations are favorable, it can react with two such groups, forming a methylene bridge between them. It is reactions of the latter type that are most likely to modify the mechanical properties of the protein. Thus, the interpretation of observed changes in the properties of the proteins is rendered extremely difficult by the multiplicity of possible reactions that must be considered. The remarkable variety of these reactions has not always been fully realized by those who have employed formaldehyde as a reagent. Some of the reactions are rapid, some are slow; some are readily reversible, some practically irreversible; some proceed readily even at room temperature, and others only at higher temperatures. Their nature is far more easily discerned when only one or two functional groups are involved, as in the amino acids and dipeptides, rather than in the more complex peptides and the proteins.

Multiple attack hypothesis of α-amylase action: Action of porcine pancreatic, human salivary, and Aspergillus oryzae α-amylases

Abstract Three conceptual action patterns of α-amylase hydrolysis of amylose have been considered: single chain, multichain, and multiple attack. To test these concepts, curves were obtained relating the drop in amylose-iodine color to the increase in reducing value for amylolysis by human salivary (HS), porcine pancreatic (PP), Aspergillus oryzae (AO) α-amylases, and 1 m H 2 SO 4 . The observed differences in the curves for the amylases could only be interpreted as due to differences in degree of multiple attack. To test these concepts further, amylase digests at various stages of hydrolysis were separated by ethanol precipitation into polysaccharide and oligosaccharide fractions. The degree of multiple attack was determined from the ratio of the reducing value of the oligosaccharide fraction to that of the polysaccharide fraction. Under optimal conditions of pH and temperature, PP had a degree of multiple attack of 6, three times that of HS or AO. At pH 4.5, the degree of multiple attack of PP did not change, although its activity was reduced 10-fold. At pH 10.5, however, the degree of multiple attack was reduced to 0.7, approaching a multichain pattern.

The Schardinger dextrins.

Publisher Summary The Schardinger dextrins are a group of homologous oligosaccharides, obtained from the breakdown of starch by the action of Bacillus macerans amylase. They bear the name “Schardinger” in recognition of the fact that, Schardinger first identified Bacillus macerans and first described their preparation and properties in reliable detail. The Bacillus macerans enzyme is distinctive in that it degrades starch with the production of almost no reducing power. Even though most enzyme preparations have a detectable hydrolytic activity (as measured by increase in copper reducing values) yet this is exceedingly small in comparison with other amylases at extents of conversion, which are similar as judged by decrease in viscosity or iodine-staining ability. At present, it is still debatable whether B. macerans amylase preparations are mixtures of two (or more) amylases, of which one has hydrolytic activity and another produces crystalline dextrins, or whether the hydrolytic activity is an intrinsic property of the same enzyme that produces crystalline dextrins. Although the enzyme has been enriched many-fold, it has so far eluded attempts to bring it into well-defined crystalline form. The usual laboratory method for obtaining B. macerans amylase is to culture the organism on an autoclaved potato or oatmeal medium in the presence of calcium carbonate at 37-45° for 2-4 weeks.

Action pattern and specificity of an amylase from Bacillus subtilis

Abstract The nature, amounts, and sequence of products formed from well-characterized substrates by the action of a crystalline α-type amylase from Bacillus subtilis were determined by qualitative and quantitative paper chromatography. The substrates studied were amylose, amylopectin, glycogen, β-amylase limit dextrins, pure individual maltodextrins, and the cyclic Schardinger dextrins. The amylase from B. subtilis showed a dual product specificity for the formation of maltotriose and maltohexaose. This dual specificity was quite pronounced when amylopectin was the substrate. The distributions of products from the interior segments of amylopectin and glycogen were completely different from the distribution of products obtained from amylose. The reactions of the maltodextrins were highly specific and dependent upon the molecular size of the dextrin. From these studies, a mechanism for the dual product specificity and action on branched substrates is proposed.

Electron microscopic observations of waxy maize starch.

Waxy maize starch (WMS) has been examined by electron microscopy to learn details of the structure of the molecules and their organization in starch granules. After dispersion in dimethyl sulfoxide WMS shows highly elongated irregular particles (molecules and aggregates) approximately 100 A in diameter and several hundred angstroms long. Granules that have been mashed in water retain vestiges of granule organization, including “growth rings” and, after negative staining, show “rippled” fibrous structures, the ripples being about 70 A apart along the fiber dimension. Thin (∼ 500-) sections of native granules show no interpretable detail, but after extensive acid treatment, the growth rings become very obvious and are composed of lamellae, about 50 A thick, oriented in an irregular pattern, more or less tangential to the growth rings. Recrystallized Naegeli amylodextrin from WMS also shows platelets about 55 A thick and several hundred angstroms in the other dimensions. We interpret the 70- ripples in the granule fragments as being alternations between amorphous and crystalline regions, the crystalline regions being due to the side-by-side association of parallel clusters of starch chains. During acid treatment, the more amorphous or gel phase of the granule gradually is eroded, the intercluster zones are hydrolyzed, and the more regular chains form crystalline lamellae. The thickness of one lamella is just the average length of a single 12- to 15-glucose unit molecular chain; that is, about 50 . We envision the molecular chains as being packed in double helices as is appropriate for the A-type Xray diffraction pattern, both before and after the acid treatment.

Multiple attack and polarity of action of porcine pancreatic α-amylase ☆

Abstract The action pattern of porcine pancreatic α-amylase on maltooctaose (G8) has been examined at pH 6.9 (optimum) and pH 10.5 (unfavorable). At pH 6.9, 27% of the G8 molecules react by multiple attack, while at pH 10.5 multiple attack is negligible. By using G8 labeled with 14C in the reducing or nonreducing end, and comparing the radioactive product distributions at pH 6.9 and pH 10.5, it was established that the direction of multiple attack is toward the nonreducing end of the substrate. The results indicate that, after initial enzymic attack, the right-hand fragment of the substrate dissociates from the enzyme surface. However, the left-hand fragment remains at the enzyme active site long enough to permit it to become repositioned and undergo further attack.

Studies on the Schardinger dextrins: XII. The molecular size and structure of the δ-, ϵ-, ζ-, and η-dextrins☆

An enzyme from Bacillus macerans which converts starch into the well-characterized cyclic α-, β-, and γ-Schardinger dextrins (cyclohexaamylose, cycloheptaamylose, cyclooctaamylose) produces at the same time small amounts of higher molecular weight dextrins. These higher dextrins, not isolable by selective complex formation, were separated by high temperature cellulose column chromatography and designated δ-, ϵ-, ζ, η-, and θ-dextrins. Evidence from dialysis, ultracentrifugal analysis, optical rotation, chromatographic mobility, enzymic hydrolysis, and fragmentation analysis indicates that the δ-dextrin is a higher homolog of the α-, β-, and γ-dextrins (cyclononaamylose). The higher fractions (ϵ, ζ, η, and θ) are mixtures of purely α −1 → 4-linked cyclic molecules with “branched” cyclic molecules and branched open-chain dextrins.

The Raffinose Family of Oligosaccharides

Publisher Summary This chapter discusses raffinose and those saccharides which are related to raffinose by virtue of having one or more α-D-galactopyranosyl groups in their structures. These D-galactosyl groups are found in nature joined to sugars, such as D-glucose, to sucrose, to certain polysaccharides, and to a few non-sugars, such as glycerol and inositol. The structural interrelations of the principal members of the raffinose family of oligosaccharides are presented in a tabulated form. The chapter discusses the preparative, and particularly the structural aspects of these compounds. These oligosaccharides occur in many varied plant sources. In several of these plants, they dominate the entire water-soluble extract, especially in members of the mint (Labiatae) and related families. Those oligosaccharides which occur primarily in seeds, roots, and underground stems are probably reserve carbohydrates. Generally, more than one of the group, together with sucrose, occurs in the same plant. These oligosaccharides may also be associated with related polysaccharides, such as the galactomannans and the sucrogalactans.

The mechanism of Q-enzyme action and its influence on the structure of amylopectin

Abstract Q-Enzyme is responsible for the synthesis of the 1,6-branch linkages in amylopectin. Its action on a model amylodextrin containing a single branch linkage has been studied. It is concluded that the enzymic process whereby the branch linkages of amylopectin are synthesized is a random action of the branching enzyme on a complex—possibly a double helix—formed between two 1,4-α-glucan chains. This action pattern predicts a novel arrangement of the units chains in amylopectin.