Creatine Kinase, BB Form (CKBB/CPK-BB/CK-1)

EC 2.7.3.2

Creatine kinase is also sometimes referred to as creatine phosphokinase, creatine phosphotransferase, CPK, or just CK. All isoenzymes of CK catalyze the phosphorylation of creatine to form phosphocreatine. Very high levels of CK are found in skeletal muscle, primarily the MM form. In the brain the BB form predominates. Phosphocreatine is used in brain tissue to regenerate ATP¹, with CK serving to catalyze the reverse reaction: The formation of ATP from phosphocreatine and ADP when ATP is needed by the tissue.

CK is a dimeric enzyme. There are two common gene products, one coding for the subunit (so named because of its predominance in muscle) and the other for the B subunit (so named because of its predominance in brain tissue). The three common forms of active CK include two homodimers and one heterodimer. The first homodimer (CK-1) consists of two B subunits and is referred to as CKBB. The other has two M subunits and is referred to as CKMM (CK-3). The heterodimer has one of each subunit and is referred to as CKMB (CK-2)². There is a third gene product which results in the mitochondrial form of CK.

CKBB is an important constituent of brain tissue, and thus the measurement of CKBB in serum and other bodily fluids can be a very useful tool in the diagnosis and prognosis of brain pathologies. This includes physical injury^3,4,5, various types of cancer^6,7 and neurodegenerative diseases such as Alzheimer’s disease⁸, CJD ⁹ (the human form of cow disease) and a host of others¹⁰. Interestingly, other forms of cancer have also resulted in clinically significant levels of elevated CKBB in serum. Examples include small cell lung cancer¹¹ and ovarian cancer¹².

There are no useful spectrophotometric changes that occur during the CK reaction, but a very common way of measuring CK activity is to couple the production of ATP in the reverse reaction with glucose and hexokinase which results in glucose-6-phosphate, which is then coupled with its dehydrogenase reaction (catalyzed by G6PDH) which uses NADP, the reduction of which can be monitored by an increase of absorbance at 340 nm.

The CK isoenzymes have different isoelectric points and thus can be readily distinguished and quantified by electrophoresis using chromogenic substrate stains.

REFERENCES

1. 1. Narayanaswami, A. Creatine Phosphokinase in Mammalian Brain. Biochemical Journal, 52, 295-301, 1952.
2. 2. Eppenberger, H.M., et. al. The Ontogeny of Creatine Kinase Isoenzymes. Developmental Biology, 10, 1-16, 1964.
3. 3. Somer, H., et. al. Brain Creatine Kinase in Blood After Acute Brain Injury. J Neurol Neurosurg Psychiatry, 38, 572-576, 1975
4. 4. Bayer, P.M., et. al., Creatine Kinase Isoenzymes in Cerebrospinal Fluid in a Case of Brain Damage. Clinical Chemistry, 22, 1405-1407, 1976.
5. 5. Skogseid, M., et. al. Increased Serum Creatine Kinase BB and Neuron Specific Enolase Following Head Injury Indicates Brain Damage. Acta Neurochirurgica, 115, 106-111, 1992.
6. 6. Zweig, M.H., et. al. Serum Creatine Kinase Isoenzyme BB as an indicator of Active Metastatic Disease. Clinical Chemistry, 25, 1190, 1979.
7. 7. Ishiguro, Y., et. al. The Diagnostic and Prognostic Value of Pretreatment Serum Creatine Kinase BB Levels in Patients with Neroblastoma. Cancer, 65, 2014-2019, 1990.
8. 8. Aksenov, M.Y., et. al. The Expression of Creatine Kinase Isoenzymes in Neocortex of Patients with Neurodegenerative Disorders: Alzheimer's and Pick's Disease. Experimental Neurology, 146, 458-465, 1997.
9. 9. Jimi., T., et. al. High Levels of Nervous Sytem-Specific Proteins in Cerebrospinal Fluid in Patients with Early Stage Creutzfeldt-Jakob Disease. Clinica Chimica Acta, 211, 37-46, 1992.
10. 10. Pfeiffer, F.E., et. al. Creatine Kinase BB Isoenzyme in CSF in Neurologic Diseases. Archives of Neurology, 40, 169-172, 1983.
11. 11. Taneja, T.K. and Sharma, S.K. Markers of Small Cell Lung Cancer. World J Surg Oncol, 2:10, 2004.
12. 12. Huddleston, H.G., et. al. Clinical Applications of Microarray Technology: Creatine Kinase B is an Up-regulated Gene in Epithelial Ovarian Cancer and Shows Promise as a Serum Marker. Gynecologic Oncology, 96, 77-83, 2005.