Temperature and Frequency Dependence of Solvent Proton Relaxation Rates in Solutions of Manganese(II) Carbonic Anhydrase

Amos Lanir*, Sonia Gradstajn, Gil Navon

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Longitudinal and transverse proton relaxation rates of water in solutions of manganese(II) bovine carbonic anhydrase have been measured by pulsed nuclear magnetic resonance spectrometry as a function of temperature (2-35°), frequency (5-100 MHz) and pH. The pH dependence of the longitudinal relaxation rate was fitted to a sigmoidal curve with a pK value at 7.8, while the esterase activity of the manganese(II) enzyme in the hydrolysis of pnitrophenyl acetate revealed an inflection point at pK = 8.2. The hydration number of manganese(ll) carbonic anhydrase could be derived using either the frequency dependence of T1p or the T1p/T2P ratio at only one (high) frequency. Both treatments are in agreement with a model in which one water molecule is bound to the metal at high pH. At low pH the relaxation data imply that no H2O exists in the first coordination sphere of the manganese ion. The various parameters which are responsible for the proton relaxation mechanisms have been evaluated and are compared to other manganese(II) enzyme systems. The pH dependence of the binding constant of manganese to apocarbonic anhydrase is also reported.

Original languageEnglish
Pages (from-to)242-248
Number of pages7
JournalBiochemistry
Volume14
Issue number2
DOIs
StatePublished - 1 Jan 1975

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