chemistry

Low-molecular-weight chromium-binding substance

Low-molecular-weight chromium-binding substance is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Low-molecular-weight chromium-binding substance rather than just read about it. In short: Low-molecular-weight chromium-binding substance (LMWCr; also known as chromodulin) is an oligopeptide that seems to transport chromium in the body. It consists of four amino acid residues; aspartate, cysteine, glutamate, and glycine, bonded with four (Cr3+) centers.

Key takeaways

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Reference excerpt

Low-molecular-weight chromium-binding substance (LMWCr; also known as chromodulin) is an oligopeptide that seems to transport chromium in the body. It consists of four amino acid residues; aspartate, cysteine, glutamate, and glycine, bonded with four (Cr3+) centers. It interacts with the insulin receptor, by prolonging kinase activity through stimulating the tyrosine kinase pathway, thus leading to improved glucose absorption. and has been confused with glucose tolerance factor. As of 2015, the exact mechanisms underlying this process were still unknown. Evidence for the existence of this protein comes from the fact that the removal of 51Cr in the blood exceeds the rate of 51Cr formation in the urine. This indicates that the transport of Cr3+ must involve an intermediate (i.e. chromodulin) and that Cr3+ is moved from the blood to tissues in response to increased levels of insulin. Subsequent protein isolations in rats, dogs, mice and cows have shown the presence of a similar substance, suggesting that it is found extensively in mammals. This oligopeptide is small, having a molecular weight of around 1 500 g/mol and the predominant amino acids present are aspartic acid, glutamic acid, glycine, and cysteine. Despite recent efforts to characterize the exact structure of chromodulin, it is still relatively unknown.

Nature of binding From spectroscopic data, it has been shown that Cr3+ binds tightly to chromodulin (Kf = 1021 M−4), and that the binding is highly cooperative (Hill Coefficient = 3.47). It has been shown that holochromodulin binds 4 equivalents of Cr3+. Evidence for this comes from in vitro studies which showed that apochromodulin exerts its maximal activity on insulin receptors when titrated with 4 equivalents of Cr3+. Chromodulin is highly specific for Cr3+ as no other metals are able to stimulate tyrosine kinase activity. It is believed to stimulate the phosphorylation of the 3 tyrosine residues of the β subunits of the insulin receptor. From electronic studies, the crystal field stabilization energy was determined to be 1.74 × 103 while the Racah parameter B was 847 cm−1. This indicates that chromium binds to chromodulin in the trivalent form. In addition, magnetic susceptibility studies have shown that chromium does not coordinate to any N-terminal amine groups but rather to carboxylates (although the exact amino acids involved are still unknown). These magnetic susceptibility studies are consistent with the presence of a mononuclear Cr3+ center and an unsymmetric trinuclear Cr3+ assembly with bridging oxo ligands. In chromodulin isolated from bovine liver, x-ray absorption spectroscopy studies have shown that the chromium (III) atoms are surrounded by 6 oxygen atoms with an average Cr—O distance of 1.98 Å, while the distance between 2 chromium (III) atoms is 2.79 Å. These results are indicative of a multinuclear assembly. No sulfur ligands coordinate to chromium and instead, it has been proposed that a disulfide linkage between 2 cysteine residues occurs owing to a characteristic peak at 260 nm.

References

Worked examples

Example 1 — a first encounter with Low-molecular-weight chromium-binding substance

Start with the simplest possible case. Write down what Low-molecular-weight chromium-binding substance claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 Low-molecular-weight chromium-binding substance 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 Low-molecular-weight chromium-binding substance 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 Low-molecular-weight chromium-binding substance

In research: Low-molecular-weight chromium-binding substance appears in chemistry 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 Low-molecular-weight chromium-binding substance 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: Low-molecular-weight chromium-binding substance is common in secondary-school and first-year university syllabi. It links to neighbouring topics Peptides, so understanding it makes those chapters shorter.
In everyday life: Look for Low-molecular-weight chromium-binding substance 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.

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How to study Low-molecular-weight chromium-binding substance in 20 minutes

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Frequently asked questions

What is Low-molecular-weight chromium-binding substance in simple terms?

Why does Low-molecular-weight chromium-binding substance matter?

Because it connects several chemistry 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 Low-molecular-weight chromium-binding substance?

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 Low-molecular-weight chromium-binding substance.