Transaminases are proteins that function as biological catalysts, facilitating chemical reactions within the body’s cells. These enzymes are part of metabolism and are specifically involved in the chemistry of amino acids, the molecules that form proteins. By mediating the transformation of these units, transaminases play a widespread role in maintaining normal physiological function.
The Biological Role of Transaminases
The primary function of transaminases is to carry out a process called transamination. This reaction involves moving an amino group from an amino acid to a keto-acid. This transfer creates a new amino acid and a new keto-acid, allowing the body to remodel these molecular building blocks as needed. This capability is important for producing non-essential amino acids, which are those the body can synthesize on its own.
This enzymatic process is part of how the body manages its nitrogen balance. The transamination reactions are reversible and depend on a coenzyme derived from vitamin B6 to proceed. Beyond amino acid synthesis, these reactions are also integrated into energy production pathways. For instance, they contribute to gluconeogenesis, a process where the liver creates glucose from non-carbohydrate sources during fasting or prolonged exercise.
Key Transaminases and Their Locations
Among the many types of transaminases, two are of particular interest in clinical contexts: Alanine Transaminase (ALT) and Aspartate Transaminase (AST). These enzymes are distinguished by their distribution throughout the body’s tissues. Understanding their locations is fundamental to interpreting their significance as health markers.
Alanine Transaminase is found in various tissues, but its concentration is highest within liver cells. This high concentration in the liver makes ALT a relatively specific indicator for the health of this organ. Its primary residence is the liver’s cytoplasm, the fluid-filled space within the cells.
Aspartate Transaminase, in contrast, has a broader distribution. Although significant amounts of AST are present in the liver, it is also found in other tissues with high metabolic activity. These locations include cardiac muscle, skeletal muscles, the kidneys, and the brain. Because of its presence in multiple organ systems, its levels can be less specific to one area compared to ALT.
Transaminases as Health Indicators
Because transaminases like ALT and AST reside and function inside cells, their levels in the bloodstream are low. The integrity of cell membranes keeps these enzymes contained where they perform their metabolic duties. These enzymes are measured in the blood as part of a routine screening like a Comprehensive Metabolic Panel (CMP) or a Liver Function Test (LFT).
The presence of elevated transaminase levels in a blood sample indicates cellular damage or inflammation. When cells are injured, their membranes can become compromised and leak their internal contents into the bloodstream. This leakage results in a measurable increase in the concentration of these enzymes. A blood test showing high transaminase levels signals that cellular distress is occurring somewhere in the body.
Interpreting Elevated Transaminase Levels
Elevated transaminase levels are a non-specific finding that prompts a deeper investigation into the underlying cause. The most frequent reason for this elevation is related to liver conditions. Non-alcoholic fatty liver disease (NAFLD), which is associated with obesity and metabolic syndrome, is a very common cause. Other liver-centric causes include:
- Alcoholic liver disease
- Viral hepatitis (such as hepatitis B or C)
- Autoimmune hepatitis where the body’s immune system attacks the liver
- Drug-induced liver injury from medications like high doses of acetaminophen
However, the liver is not the only source of these enzymes. Strenuous physical activity can lead to a temporary spike in transaminase levels, particularly AST, due to muscle cell breakdown. Direct muscle injuries, underlying muscle disorders (myopathies), celiac disease, and some thyroid disorders can also cause elevations.
Healthcare providers analyze the specific levels and the ratio of AST to ALT to gather clues about the potential cause. For instance, in alcoholic liver disease, the AST level is often significantly higher than the ALT level. The degree of elevation also provides information; mild elevations are common in fatty liver disease, while much higher levels might suggest acute viral hepatitis or a toxic injury.