Difference Between Actin and Myosin

Thekey difference在肌动蛋白和肌球蛋白之间actin exists as thin, short filaments while myosin exists as thick, long filaments inmyofibrils的muscle fibers.

肌动蛋白-myosin contractile system is the main contractile system of all muscular tissues, and it works based on the interactions between the two proteins – the actin and myosin. Furthermore, these two proteins exist as filaments in muscles, and their association is mainly responsible for the muscular movements.

内容

1.Overview and Key Difference
2.What is Actin
3.What is Myosin
4.Similarities Between Actin and Myosin
5.Side by Side Comparison – Actin vs Myosin in Tabular Form
6.概括

什么是肌动蛋白？

肌动蛋白is the most abundant protein in the muscle fibers, and it is responsible formuscle contraction. It can exist in two distinct forms within the cell. They are globular actin (G-actin) or filamentous actin (F-actin). G-actin is a ≈43kDa protein that can bind ATP and polymerize to form microfilaments known as F-actin filaments. F-actin filaments have appositive (+) ends and negative (-) ends. Both ends are highly dynamic, but have different on/off rates; growth of filaments occurs primarily at the positive end as it has a much higher “on” rate.

肌动蛋白丝是高度交联的，并被蛋白（例如α-肌动蛋白）捆绑在一起，以增加其结构完整性。细胞肌动蛋白网络将其高度动态的性质归功于肌动蛋白相互作用的蛋白质，从而促进其组装，稳定和拆卸。

What is Myosin?

Myosins are a family of motor proteins associated with actin. Actin-myosin complexes generate the cellular forces used in cell contractility and migration. The majority of myosins are (+) end motors, i.e., they move along actin filaments towards the (+) end. There are several different types of myosins, and each participates in specific cellular functions. Myosin “heavy chains” consist of one or more head, neck, and tail domains.

Functionally, myosins also strengthen the actin network by cross-linking actin fibers. Myosin uses ATP to produce energy; thus, it initiates the muscle contraction by forcing its head towards the actin fiber. One myosin molecule produces about 1.4 pN of force when it changes the confirmation.

What are the Similarities Between Actin and Myosin?

• 肌动蛋白和肌球蛋白是两种蛋白，作为细丝。
• They are present in muscle cells.
• 同样，肌肉收缩是肌动蛋白和肌球蛋白相互作用及其关联的结果。
• Besides, they are arranged longitudinally in myofibrils.

What is the Difference Between Actin and Myosin?

肌动蛋白filaments are thin, short filaments, and myosin filaments are thick, long filaments. So, we can take this as the key difference between actin and myosin. Besides, actin filaments occur in two forms: monomeric G-actin and polymeric F-actin. Whereas, myosin molecule has two components: a tail and a head. The tail is formed of heavy meromyosin (H-MM) while the head is formed of light meromyosin (L-MM). Thus, this is another difference between actin and myosin.

Moreover, a further difference between actin and myosin is that the actin forms both A and I bands whereas myosin forms only A bands (A-band forms the dark各向异性band of myofibril, and I-band forms the light isotropic band of myofibril). Additionally, ATP only binds to myosin ‘head’, and it does not bind to actin. Furthermore, unlike actin, myosin produces a force by binding ATP in order to initiate muscle contractions. Hence, this is also a difference between actin and myosin.

Below infographic on the difference between actin and myosin provides more differences between both comparatively.

概括– Actin vs Myosin

肌动蛋白和肌球蛋白是肌肉细胞中存在的两种类型的蛋白质。肌动蛋白在肌原纤维中产生薄细丝，而肌球蛋白则产生浓密的细丝。两种类型的蛋白质丝都是肌肉收缩和运动的原因。他们相互互动并帮助肌肉收缩。此外，肌肉纤维中存在相对较多的肌动蛋白丝。此外，与肌球蛋白丝不同，肌动蛋白丝与Z线条并滑入H区。但是，与肌动蛋白丝不同，肌球蛋白丝形成了十字架。因此，这总结了肌动蛋白和肌球蛋白之间的区别。

Reference:

1. Cooper，Geoffrey M.“肌动蛋白，肌球蛋白和细胞运动。”当前的神经病学和神经科学报告。美国国家医学图书馆，1970年1月1日，Available here.

Image Courtesy:

1. “F-actin filaments in cardiomyocytes” By Ps1415 – Own work(CC BY-SA 4.0)viaCommons Wikimedia
2. “Actin-myosin” By Jeff16 – Own work(CC BY-SA 4.0)viaCommons Wikimedia