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Abstract
A new titration calorimeter is described and results are presented for the binding
of cytidine 2'-monophosphate (2'CMP) to the active site of ribonuclease A. The instrument
characteristics include very high sensitivity, rapid calorimetric response, and fast
thermal equilibration. Convenient software is available for instrument operation,
data collection, data reduction, and deconvolution to obtain least-squares estimates
of binding parameters n, delta H degree, delta S degree, and the binding constant
K. Sample through-put for the instrument is high, and under favorable conditions binding
constants as large as 10(8) M-1 can be measured. The bovine ribonuclease A (RNase)/2'CMP
system was studied over a 50-fold range of RNase concentration and at two different
temperatures. The binding constants were in the 10(5) to 10(6) M-1 range, depending
on conditions, and heats of binding ca. -15,000 cal/mol. Repeat determinations suggested
errors of only a few percent in n, delta H degree, and K values over the most favorable
concentration range.