The effect of substrate and potassium on the inhibitory kinetics of mnci2 on the enzyme k+-p-nitrophenyl phosphatase in rat brain

✍ Scribed by S. K. Bansal; Tahir Husain; R. C. Murthy; S. V. Chandra

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: English
• Weight: 385 KB
• Volume: 5
• Category: Article
• ISSN: 0260-437X
• DOI: 10.1002/jat.2550050107

✦ Synopsis

The effect of MnZ+, a divalent metal, on the enzyme K+-p-nitrophenyl phosphatase (K+-PNPPase) was studied in rat brain. The metal was found to be a moderate inhibitor of the enzyme, with an Is0 of approximately 4 8 0 ~~. The inhibition was pH dependent, but not temperature dependent. On measurement of the inhibition with varying concentrations of PNPP (1-5 mM), the I50 value remained constant. However, when the inhibition was measured with K+ (5-20 mM), the Is0 value increased from 130 pM to 490 PM, suggesting that K+ antagonized the effect of Mn2+. In kinetic studies, MnZ+ inhibited the enzyme in a non-competitive manner with respect to PNPP. The K, remained constant (2.9), but the Vmax was decreased from 5.0 to 1.6. However, with respect to K+, the inhibition was competitive, as the concentration for half maximal activation (Ko.5) increased from 1.3 to 8.9 mmoll-' with 1 mM of MnCI,, suggesting that the apparent affinity of K+ for the enzyme was decreased. The apparent Vmax was not affected. The degree of cooperativity (n) measured as the slope of the Hill plot remained unaltered (1.9 f 0.2) over the entire concentration range of MnCl, tested.