Kallikreins homology

With few exceptions, an increase in the activity or mass of an enzyme or isoenzyme is not specific or sensitive enough to be used for identifying the type of cancer or the specific organ involvement. An exception is PSA. PSA has mild protease activity and amino acid sequence homology with serine protease of the kallikrein family.It is expressed by normal, benign, hyperplastic, and cancerous prostate glands and minimally by other tissue. Until the application of PSA as a marker for prostate cancer, tumor enzymes had lost most of their popularity for use as cancer markers. Enzymes were used historically as tumor markers before the discovery of oncofetal antigens and the advent of monoclonal antibodies. The abnormalities of enzymes as a marker for cancer are either the expression of the fetal form of the enzyme (isozyme) or the ectopic production of enzymes. 

Kallikreins, a family of serine proteases from which human tissue kallikreins, hKs, represent the largest contiguous cluster of protease genes in the human genome. The hKs (EC 3.4.21.35) are homologous serine... 

The five inhibitors were also tested against mouse plasma kallikrein (79% sequence identity) or the homologous human serine proteases factor XIa (63% sequaice identity) and thrombin (36% sequence identity). None inhibited these enzymes at the highest concentration tested (10 pM). 

Fujikawa, K., Chung, D.W., Hendrickson, L.E., and Davie, E.W., 1986, Amino acid sequence of human factor XI, a blood coagulation factor with four tandem repeats that are highly homologous with plasma kallikrein. Biochemistry 25 2417-2424. 

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