Calcium and TNFα additively affect the chondroitinase ABC I activity

Experimental models have repeatedly shown the therapeutic potential of cABC I in spinal cord injury (SCI) by degrading chondroitin sulfate proteoglycans that hinder neurite outgrowth. Following SCI, some molecules are released from injured cells. This study is designed to determine the effects of some of these molecules at the SCI loci on activity, stability and structure of wild type and Q140A variant of cABC I. The effect of Ca²⁺, ATP, adenosine, Asp, Glu, Gln, TNFα, and a combination of them in physiologic and pathologic concentrations was assessed. The results showed that Ca²⁺ and TNFα have increasing and additive effects on the enzymes activity. Meanwhile, the other molecules had neither considerable effect on the activity nor on thermal stability of the enzymes, significantly. Structural analyses of wild type and mutant cABC I in the presence and absence of Ca²⁺ were also carried out using fluorescence and far-UV circular dichroism techniques. Although, the secondary and tertiary structure of enzymes showed no significant alterations in the presence of Ca²⁺, but fluorescence quenching data indicated that calcium increases flexibility of the wild type enzyme, slightly. Therefore, it can be concluded that this ion affect enzyme activity without remarkable conformational changes.