Isolichenan

Key takeaways

Isolichenan belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Isolichenan to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Isolichenan from memory before moving on to harder problems.

Reference excerpt

Isolichenan, also known as isolichenin, is a cold-water-soluble α-glucan occurring in certain species of lichens. This lichen product was first isolated as a component of an extract of Iceland moss in 1813, along with lichenin. After further analysis and characterization of the individual components of the extract, isolichenan was named in 1881. It is the first α-glucan to be described from lichens. The presence of isolichenan in the cell walls is a defining characteristic in several genera of the lichen family Parmeliaceae. Although most prevalent in that family, it has also been isolated from members of the families Ramalinaceae, Stereocaulaceae, Roccellaceae, and Cladoniaceae. Experimental studies have shown that isolichenan is produced only when the two lichen components – fungus and alga – are growing together, not when grown separately. The biological function of isolichenan in the lichen thallus is unknown.

Early studies

Isolichenan was first isolated from Cetraria islandica in 1813 by Swedish chemist Jöns Jacob Berzelius, who also at the same time isolated the cellulose-like hot-water-soluble glucan lichenan. Because in these experiments the isolichenan component of the lichen extract had a positive reaction with iodine staining (i.e. production of a blue colour), Berzelius thought it to be similar in nature to starch, and he called it "lichen starch". It was thought to function as a reserve food source for the organism. Later studies showed it to be a mixture of polysaccharides. In 1838, Gerardus Johannes Mulder isolated the blue-staining component of the C. islandica extract, believing it to be starch. Friedrich Konrad Beilstein gave the name "isolichenan" to this substance in 1881. Isolichenan was the first α-glucan described from lichens. In 1947, Kurt Heinrich Meyer and P. Gürtler, discussing the preparation of lichenan, reported that the mother liquor contained a water-soluble glucan that could be purified by repeated freezing and thawing. In this process, which completely removed lichenan, they obtained isolichenan in a 0.55% yield.

Structure Isolichenan is a polymer of glucose units joined by a mixture of α-(1→3) and α-(1→4) linkages. Using the technique of partial acid hydrolysis, Stanley Peat and colleagues determined that the linkages are of the α-configuration. The ratio of these linkages has been reported differently by various authors in the scientific literature: 11:9, 3:2, 2:1, 3:1, and 4:1. Fleming and Manners found the ratio to be 56.5:43.5 and 57:43 in two separate experiments using the Smith degradation procedure. This technique uses the successive steps of periodate oxidation, borohydride reduction, and mild acid hydrolysis; in this way, acetal linkages become hydrolysed, but glucosidic linkages are not. The distribution of linkages in isolichenan was found to be somewhat irregular, with both types occurring in groups of two or more in at least some areas. Another study suggests that isolichenan has mostly groups of one or two α-(1→3) bonds surrounded by α-(1→4) bonds. Compared with, for example, amylose (a linear α-(1→4)-linked glucan and the major component of starch), isolichenan has a relatively weak iodine-staining reaction. This weak staining intensity is thought to be a result of its preponderance of (1→3) linkages, a property that reduces the formation of the polyiodide-complex that gives the positive reaction its blue colour. The chain length of isolichenan was estimated at 42–44 glucose units. The reported molecular weight of isolichenan also varies, from 26 kD to 2000 kD. The relatively short chain length of isolichenan may explain why it is soluble in cold water after it has been extracted from the lichen thallus. Purified isolichenan has a high positive specific rotation in water. It has been reported as high as +272, although different sources give differing values. The term "isolichenan-type" has been used as a general term for α-D-glucans having (1→3)-(1→4) linkages in their main chain. Similar to isolichenan, the α-D-glucan known as Ci-3 consists of 1→3 and 1→4 linked α-D-glucose residues in ratio of 2:1, but with a much higher degree of polymerization and a molecular weight of about 2000 kD. It is also found in Cetraria islandica. As the discrepancies in reported values demonstrate, lichens produce isolichenan-type polysaccharides with considerable variation in linkage ratios as well as molecular weight, even within the same species. The carbon-13 nuclear magnetic resonance spectrum of isolichenan was reported by Yokota and colleagues in 1979 and also by Gorin and Iacomini in 1984.

Occurrence Since its discovery in Cetraria islandica, isolichenan has been isolated from many other lichen species. It is predominant in the Parmeliaceae, a large and diverse family of the class Lecanoromycetes. Parmeliaceae genera and species containing isolichenan include: Alectoria (A. sulcata, A. sarmentosa); Cetraria (Cetraria cucullata, C. islandica, C. nivaris, C. richardsonii; Evernia (E. prunastri); Letharia (L. vulpina); Neuropogon (N. aurantiaco-ater); Parmelia (P. caperata, P. cetrarioides, P. conspersa, P. hypotrypella, P. laevior, P. nikkoensis, P. saxatilis, P. tinctorum); Parmotrema (P. cetrarum, P. araucaria, P. sulcata); and Usnea (U. barbata, U. baylei, U. faciata, U. longissima, U. meridionalis, U. rubescens). A few members of the family Ramalinaceae have been shown to contain isolichenan, including Ramalina celastri, R. ecklonii, R. scopulorum, and R. usnea. In the family Stereocaulaceae, isolichenan has been isolated from S. excutum, S. japonicum, and S. sorediiferum. It is also known to occur in single species in the Roccellaceae (Roccella montagnei) and the Cladoniaceae (Pilophorus acicularis).

Uses

Although isolichenan is not nearly as constant at the genus level as lichenan, the presence of isolichenan in the cell walls is a defining character in several genera of the lichen family Parmeliaceae, including Asahinea, Cetrelia, Flavoparmelia, and Psiloparmelia. In contrast, the absence of isolichenan is a character of genus Xanthoparmelia. Isolichenan is used as an active ingredient in cough lozenges as a component of Cetraria islandica extract.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Isolichenan

Start with the simplest possible case. Write down what Isolichenan claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Isolichenan before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Isolichenan ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Isolichenan

In research: Isolichenan appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Isolichenan in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Isolichenan is common in secondary-school and first-year university syllabi. It links to neighbouring topics Lichen products, Polysaccharides, so understanding it makes those chapters shorter.
In everyday life: Look for Isolichenan outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Isolichenan in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Isolichenan means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Isolichenan out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Isolichenan in simple terms?

Isolichenan, also known as isolichenin, is a cold-water-soluble α-glucan occurring in certain species of lichens. This lichen product was first isolated as a component of an extract of Iceland moss in 1813, along with lichenin.

Why does Isolichenan matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Isolichenan?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Isolichenan.