The key difference between allozymes and isozymes is that allozymes are coded by different alleles at the same locus. But, in contrast, isozymes are coded by genes at different loci.
Enzymes are biocatalysts that speed up biochemical reactions. In fact, they are protein molecules coded by genes. There are different types of enzymes. Some enzymes are coded by different alleles of the same gene present at the same locus. They are known as allozymes. In contrast, some enzymes are coded by different genes located at different loci. These enzymes are known as isozymes. Isozymes and allozymes can be used to determine the relationship between two organisms.
CONTENTS
1. Overview and Key Difference
2. What are Allozymes
3. What are Isozymes
4. Similarities Between Allozymes and Isozymes
5. Side by Side Comparison – Allozymes vs Isozymes in Tabular Form
6. Summary
What are Allozymes?
Allozymes are variants of an enzyme coded by different alleles present at the same locus. Therefore, multiple alleles at one locus code for allozymes. They show a small difference in their amino acid sequences or structure. However, they carry out a very similar function. The small differences existing among allozymes is due to the mutations, or random changes occurred in DNA sequences. These tiny differences can be detected by capillary electrophoresis based on the molecular sizes and electrical charges.
Allozymes can be used as a marker of species relatedness. Hence, they can explain the evolutionary history of an organism and act useful as markers for mapping family trees between different species within the same genus. Therefore, allozymes are frequently used to map closely related species in different groups, including plants and animals. If the organisms are closely related, there would be fewer changes between allozymes.
What are Isozymes?
Isozymes are variants of an enzyme coded by different genes located at different loci. In simple words, isozymes are multiple forms of an enzyme coded by different genes. Structurally, isozymes slightly differ from their amino acid sequences. Hence, they consist of different shapes and sizes. But they catalyze the same biochemical reaction.
Figure 01: Isozymes
However, they are capable of working under various conditions, at different locations in our body or at different stages or in a variety of cellular conditions.
What are the Similarities Between Allozymes and Isozymes?
- Both allozymes and isozymes are proteins that act as biological catalysts of biochemical reactions.
- They have slightly different amino acid sequences.
- Both types are useful in determining evolutionary relationships between closely related organisms.
- Gel electrophoresis is one of the techniques that can be used to isolate allozymes and isozymes.
What is the Difference Between Allozymes and Isozymes?
A single gene produces multiple forms of an enzyme called allozymes. In contrast, different genes produce multiple forms of an enzyme called isozymes. Therefore, this is the key difference between allozymes and isozymes. Allozymes are coded by different alleles at the same locus while isozymes are coded by different genes at the different loci.
Summary – Allozymes vs Isozymes
Allozymes and isozymes are two forms of enzymes. Allozymes are multiple forms of an enzyme coded by the different alleles present in one locus. Isozymes are also multiple forms of an enzyme but coded by different genes present in different loci. Allozymes differ from each other by amino acid sequences. Similarly, isozymes differ from each other by the amino acid sequence. However, all allozymes carry out the same function. Similarly, all isozymes catalyze the same chemical reaction. So, this is the summary of the difference between allozymes and isozymes.
Reference:
1. “Allozyme: Definition & Electrophoresis.” Study.com, Study.com, Available here.
2. “Isozyme.” Wikipedia, Wikimedia Foundation, 30 Dec. 2019, Available here.
Image Courtesy:
1. “Isoenzyme2” By علاء – Own work (CC BY-SA 4.0) via Commons Wikimedia