Myoglobin

Myoglobin is one of the most important proteins in the human body. It is found in smooth and skeletal muscle tissue; where it binds oxygen and provides energy to power muscular contractions. It is an iron-oxygen binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is found in skeletal and cardiac muscles. It is a Hemeprotein that facilitates intracellular oxygen storage and transcellular diffusion of oxygen. Myoglobin's affinity for oxygen is higher than hemoglobin. And unlike hemoglobin which is found in the red blood cells, Myoglobin is found in muscle tissues. Myoglobin, together with the cytochromes, is responsible for the red-brown color of muscles.

In 1958, scientists Max Perutz and John Kendrew determined the 3D structure of Myoglobin by X-ray crystallography and interestingly, Myoglobin is the first protein to have its three-dimensional structure determined. In 1962, both these eminent scientists shared the Nobel prize for constructing a three-dimensional model of crystalline sperm-whale Myoglobin utilizing the technique of X-ray diffraction.

Myoglobin structure and functions

• Myoglobin transports or stores oxygen in muscles. Unlike other proteins, myoglobin is able to bind with oxygen because it contains Heme,a metal-containing prosthetic group that allows it to bind to oxygen.
  
  
• Myoglobin consists of a single polypeptide chain
  
  
• Myoglobin occurs as a monomeric heme protein
  
  
• Myoglobin contains only one heme binding sub-unit surrounded by a globular protein, containing eight alpha-helical and six non helical segments, made up of 153 amino acids.
  
  
• During the period of oxygen deprivation, oxymyoglobin releases its bound oxygen for metabolic purposes.
  

Myoglobin test results

For Men: 10 - 95 ng/ml (onset: 1-3 hrs, peak: 6-10 hrs, return to normal: 12-24 hrs)

For Women: 10 - 65 ng/ml (onset: 1-3 hrs, peak: 6-10 hrs, return to normal: 12-24 hrs)

Myoglobin Test

Myoglobin serum test may be used detect muscle damage. Myoglobin is rapidly released after muscle damage, and thus can be a useful bio marker in the early phases of muscle injury. When heart or skeletal muscle is injured, Myoglobin is released into the blood. When the damage is severe, Myoglobin levels in the blood shoot up within few hours of damage.

Excess Myoglobin in the blood is filtered by kidneys and released into the urine. And thus, severe muscle damage followed by high amounts of Myoglobin in the serum and eventually in the urine may lead to renal failure. Myoglobin levels are tested to identify the presence and timing of muscle damage. However, it cannot determine the location of muscle injury/damage. The Myoglobin blood test is also commonly used to identify a recent heart attack or acute myocardial infarction. Other sensitive markers like troponin are more commonly used today to detect heart conditions.

CK blood test

A Creatinine Kinase test is a blood test that measures the levels of Creatinine phosphokinase (CPK). It is an enzyme found predominantly in the heart tissue, brain and skeletal muscle. The CK blood test is commonly used to diagnose the existence of heart muscle damage. The CK blood test result shows an increase above normal in a person's blood test about six hours after the start of a heart attack.

It reaches its peak in about 18 hours and returns to normal in 24 to 36 hours. When the total CPK level is substantially elevated, then it is indicative of injury or stress to heart, brain or skeletal areas. The small amount of CPK that is normally in the blood comes from the muscles. The CPK blood test also helps in cost-effective management of people with suspected coronary atherosclerosis. It also evaluates the extent of muscle damage caused by drugs, trauma or immobility.

Abnormal CK-MB (one of three CK isoenzymes) or troponin levels are associated with Myocyte Necrosis and the diagnosis of Myocardial infarction. The Cardiac Markers of Cardiac Myocyte Necrosis (damage to the Cardiac muscle cells), myoglobin, CK, CK-MB and troponin I and T are primarily used to identify acute Myocardial Infarction.

It is used in early detection of dermatomyositis and polymyositis. It is also used to distinguish malignant hyperthermia from a post operative infection. It helps to discover carriers of muscular dystrophy.

The normal range for Creatinine Kinase (CK or CPK) blood test:
Male: 38 - 174 units/L
Female: 96 - 140 units/L

Increased levels of CK also can be found in viral myositis and hypothyroidism. Higher than normal CPK levels is indicative of the following conditions:

• Heart attack
  
• Myocarditis
  
• Convulsions
  
• Delirium Tremens
  
• Electric shock
  
• Muscular dystrophy
  
• Pulmonary infarction
  

CK MB

Serum CKMB levels are tested to check for myocardial injury. It is another important cardiac marker. The primary source of CKMB is myocardium although it is also found in skeletal muscle. Typically CKMB tests have now been replaced by Troponin test. But in cases of abnormal Troponin assay results or suspected re-infarction in the hospital, the CKMB serum test is still used.

High levels of CK MB are noticed in cases of polymyositis and rhabdomyolysis. Patients suffering pulmonary embolism, hypothyroidism, and muscular dystrophy or carbon monoxide poisoning can also show higher levels of serum CKMB. The reference range is about 56.2 pg/mL.