Adenosine Deaminase (ADA; E.C. no. 3.5.4.4.) in Colorectal Adenocarcinoma in Man

Abstract

Soluble ADA is known to occur in different isozymes in man. Two major forms have been identified in the normal human tissues: the so called red cell ADA or ADA-S, a monomeric protein, with a M.W. of about 35KD (kilodaltons), and a tissue specific form, or ADA-L, of about 300KD, composed of a dimeric glycoprotein molecule (adenosine deaminase complexing protein=ADCP) and two molecules ADA-S. Additional ADA isozymes have been reported by several authors: a form of 435KD in the normal intestine, a so called particulate form in different tissues probably due to membrane bound ADA⁴ and a cancer specific 70KD in some colorectal tumors⁵. Nishihara et al.⁶ observed that free ADCP, usually present in normal lung tissue, was strongly decreased in the extracts of cancerous lung. Trotta and Balis presented evidence for the absence of ADCP in a clear cell carcinoma of the kidney, in spite of the fact that normal kidney is the major source of free ADCP. In the same report they described a striking decrease of ADA-L, thus of ADCP, in 14 out of 15 colorectal tumors. These data and the data presented by Herbschleb-Voogt et al. (this conference), where ADA-L was found to be almost absent or markedly decreased in 6 transformed- and tumor derived cell lines, formed the basis for the present investigation.