[The enzymatic character of myeloma cell]

Thymidine kinase (TK) is a cellular enzyme required for the incorporation of thymidine into DNA. It catalyses the conversion of deoxythymidine to deoxythymidine monophosphate (dTMP). The synthesis of dTMP from deoxythymidine is called the salvage pathway. There are two types of thymidine kinase, distinguished by there biochemical and physico-chemical characteristics. Cytosolar TK is found in dividing cells in stages G1-S. Mitochondrial TK is found in mitochondria. Serum thymidine kinase (S-TK) levels can be determined by the use of a radioenzyme assay method. These are increased in proliferating cells (S phase). It is a useful tool for the clinical evaluation, staging, and follow-up of patients with multiple myeloma.