Regulation of the Enzyme Activity of Carp Nephrosin Involves Ca2+ and Heparin

• Main Authors: Kuo, Hon-Yi, 郭弘億
• Other Authors: Chang Geen-Dong
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/14123705081936925351

碩士 === 國立臺灣大學 === 生化科學研究所 === 86 === Nephrosin is a newly discovered member of the astacin family, a group of secreted or membrane metalloproteinases found in the 1990s. It is the fir st astacin enzyme found in lymphohematopoietic tissues (kidney, head kidney , and spleen in fish). Carp nephrosin in its secreted form contains 198 amino acid residues whose predicted relativemolecular weight is 23k. Four puta tive heparin binding motifs can be identified by which secreted nephrosin ma y be localized to the heparan sulphate proteoglycan present in extracellular m atrix. In this thesis, we examined the metal ion requ irement for the activation of purified nephrosin (apoenzyme). It is concluded that in addition to the catalytic Zn2+ binding site (Zn site), nephrosi n contains a Ca2+ binding site since Ca2+ (0.2-0.8mM) can further enhan ce the activity of nephrosin when it is activated by 100mM Zn2+. Pontential agonists for the Zn site of nephrosin include Zn2+, Mn2+, Co2+, Cu2+, Ni2+ an d Cd2+, and potential agonists for the Ca site include Mn2+, Co2+, Cu2+, Ca2+, Sr2+ and Mg2+. It was also observed that hep arin reduced nephrosin activity when nephrosin was activated by Zn2+ (100mM ) but lost its inhibitory activity when nephrosin was co-activated by Zn2+ (100mM) and Ca2+ (500mM). It is postulated that nephrosin is stored in its mature form but its activity is prohibited by binding to heparin or hepa rin-like glycosaminoglycan. Once nephrosin is secreted into the extracellula r fluid, exposure to higher concentrations of extracellular Ca2+ may remo ve the inhibitory action of heparin and thus convert the inactive form into f ully active form.