Measurements of proton relaxation time T2 on cattle eyes lenses.

A simple two phase model does not explain the temperature dependence of T1 relaxation time in lenses as biological systems. Therefore, a distribution of correlation times of water particles has to be assumed by a certain distribution of the water protein binding energy. As a consequence, from the temperature dependence of T1 relaxation time, the activation energy of water molecules in the lens cannot be evaluated directly without the knowledge of the distribution width. This problem can be solved by T2 measurements in lenses. From the slope of T2 as a function of temperature, mean activation energy can be calculated independently on the distribution width. Measurements were performed on lenses originating from 5-7 years old cows, 2-year old bull-calfs and a 12-year old bull in the temperature range -30 to +105 degrees C. It could be demonstrated that about 80% of water behaves as liquid-like water with an activation energy 14 +/- 4 kJ/mol corresponding to the value of free water. The remaining water (about 20%) is bound to the protein with an activation energy of 20 +/- 5 kJ/mol. At 42 degrees C the protein denaturation process starts in the eye lens and will be completed by 70 degrees C, yielding a protein bound-water complex.