Question

Which of the following is an example of isozyme? (a) \(\alpha\)-Amylase (b) Glucokinase (c) Lactate dehydrogenase (d) All of these

Short answer

(d) All of these. Each of the enzymes listed has different isozyme forms that perform the same function in different tissues or conditions.

Step-by-step solution

Definition of Isozyme

Understand what an isozyme is. An isozyme (also known as isoenzyme) is one of several different forms of an enzyme that catalyze the same reaction but differ in amino acid sequence, regulatory properties, and other characteristics. They often differ in the tissue distribution and the physiochemical properties but perform the same function.

Identify Isozymes Among the Options

Examine each option to determine whether it fits the definition of an isozyme.\( \alpha \)-Amylase has different isozymes for digesting starch in different tissues. Glucokinase is a specific isozyme of hexokinase that is expressed in the liver and pancreatic beta cells. Lactate dehydrogenase has multiple isozyme forms that are found in different body tissues and have different kinetics.

Conclusion

After evaluating all options against the definition of isozymes, we find that each given option is an example of an isozyme as each has different forms that catalyze the same biochemical reactions in various tissues or under different conditions.

Key concepts

Enzyme Specificity

Enzyme specificity is a fundamental concept in biochemistry that refers to the ability of an enzyme to choose exact substrates and catalyze specific biochemical reactions. Think of an enzyme as a specialized key designed to open a particular lock, where the lock represents the substrate and the key opening the lock is the enzyme catalyzing a reaction. What makes an enzyme 'specific' is its unique three-dimensional structure, which determines which substrate it can bind to. Consequently, although enzymes may be very similar in nature, small variations in their structure can allow them to distinguish between substrates with similar structures.

Similarly, isozymes exemplify enzyme specificity because they can catalyze the same reaction but do so in different tissues or under diverse physiological conditions, often because they have slightly different structures or regulatory mechanisms. This specificity underlies the efficient and precise regulation of metabolism in response to the body's ever-changing needs.

Enzyme Catalysis

Enzyme catalysis is a central theme in understanding biochemical processes. Enzymes are remarkable biomolecules that enhance the rate of reactions without being consumed in the process. The secret to an enzyme's catalytic prowess lies in its ability to lower the activation energy barrier - the hurdle that reactants must overcome to convert into products.

Enzymes operate by providing an alternative pathway for the reaction, typically through the formation of an enzyme-substrate complex. This temporary complex is stabilized by various interactions within the active site of the enzyme, effectively making it easier for the reaction to proceed. Not only do enzymes speed up reactions, but their catalytic activity is also highly controlled and influenced by environmental factors such as pH, temperature, and the presence of inhibitors or activators.

Biochemical Reactions

Biochemical reactions are the crux of life, facilitating the complex interplay of molecules within living organisms. These reactions are typically mediated by enzymes, allowing life-sustaining processes to proceed at rates fast enough to support life's exigent demands.

The metabolism within an organism is a vast network of biochemical reactions that convert substrates into products, involving energy transformations and the generation of biomolecules necessary for growth, repair, and replication. Isozymes play a pivotal role in this network as they can regulate these reactions in a tissue-specific manner, ensuring that a particular reaction occurs where and when it is needed in the body. For example, an isozyme might be more active in the heart muscle, where rapid energy conversion is necessary, and less active in another tissue where the demand for such activity is lower.

Lactate Dehydrogenase

Lactate dehydrogenase (LDH) is a prime example of an enzyme that exists in the form of isozymes. LDH is key in the process of anaerobic respiration, particularly during vigorous exercise when oxygen supply to muscles is limited. It catalyzes the conversion of pyruvate to lactate along with the regeneration of NAD+, which is crucial for sustained energy production in the absence of oxygen.

LDH isozymes vary in their distribution throughout the body and in their kinetic properties. Some isoforms of LDH are found predominantly in the heart and are more efficient at catalyzing reactions at lower substrate concentrations, while others are present in muscle tissues with different kinetic characteristics suited to that environment. Thus, the study of LDH and its isozymes not only illustrates the concept of enzyme specificity and catalysis but also exemplifies the dynamic nature of biochemical reactions, reflecting the meticulous orchestration of metabolic processes in response to physiological demands.