The thermodynamics of calcium binding to thermolysin

Calcium binding isotherms were determined for thermolysin in the range pH 5.6-10.5, and from 5 to 45 degrees C. An extensive statistical analysis of the binding data suggests that at least two of the four binding sites bind Ca2+ with complete positive cooperativity and independently of the other two. Nonlinear regression analysis of the binding data was used to calculate cooperative (K1) and independent (K2) binding constants for the four calcium sites. Thermodynamic parameters obtained from a van't Hoff analysis indicate that calcium binding to both cooperative and independent sites is an entropy-driven process. At pH 7.0, delta H1 = 90.4 kJ/mol; delta H2 = 97.5 kJ/mol; delta S1 = 456 J K-1 mol-1; delta S2 = 262 J K-1 mol-1. These results are compared to those obtained for other calcium-binding proteins. An analysis of the pH dependence of the calcium binding constants indicates that the binding of four protons at the cooperative site and one to two protons at the independent sites, modulates the calcium affinity. This confirms an earlier structural assignment of the double-site as the locus of the two cooperatively binding Ca2+. Calcium binding to thermolysin is enhanced in the presence of an active site directed inhibitor, suggesting that there may be positive cooperativity between substrate and calcium binding.     

131I]metaiodobenzylguanidine and high-dose chemotherapy with bone marrow rescue in advanced neuroblastoma.

High-dose chemotherapy (HDT) and autologous bone marrow rescue (ABMR) is routinely used as consolidation treatment in advanced neuroblastoma. This study is presently examining the efficacy and toxicity of combined [131I]metaiodobenzylguanidine (131I-MIBG) therapy with HDT and ABMR. Five children (4 male, 1 female), median age of 8 years (range 4-11 years) were treated, 3 at relapse and 2 after initial chemotherapy. A single infusion of 131I-MIBG (median activity 11.1 GBq, range 7.4-11.2 GBq) was followed by HDT and ABMR 14-32 days later. High-dose chemotherapy consisted of carboplatin and melphalan in 4 patients, and vincristine, etoposide, carboplatin and melphalan in 1. One patient developed a septicaemia and died, and another failed to engraft; both had extensive bone marrow infiltration at the time of 131I-MIBG therapy. The combined therapy was well tolerated by the three other patients. Two children have relapsed and died (including one who failed to engraft), and 2 are alive 17 and 41 months after ABMR. In the absence of extensive bone marrow metastases, combined therapy offers potential as a means of consolidating treatment in advanced neuroblastoma.