S-adenosyl-L-homocysteine: simplified enzymatical preparation with high yield.

S-adenosyl-L-homocysteine hydrolase catalyses the synthesis of S-adenosyl-homocysteine (AdoHcy) from adenosine (Ado) and L-homocysteine (L-Hcy) in the absence of other enzymes, such adenosine deaminase, using Ado or L-Hcy as a substrate. Studies concerning the effect of substrates and enzyme concentrations with enzyme from beef liver, an inexpensive enzyme source, allowed the determination of the smallest amount of enzyme leading to total conversion to AdoHcy for the highest Ado and L-Hcy concentrations. Washing out the blood, homogenization of beef liver slices at pH 4.9 and precipitation with between 40% and 50% saturated (NH4)2SO4 eliminated contamination of tissue by blood adenosine deaminase. This enzyme preparation transforms Ado only into AdoHcy in the presence of L-Hcy. In a 1 1 final volume, an amount of enzyme preparation corresponding to at least 18.5 mg of fresh liver causes the total transformation of 60 mM Ado in the presence of 90mM L-Hcy after 40 hours incubation at 37 degrees C and pH 6.8. After purification by two crystallizations, the AdoHcy yield, based upon the Ado incubated, is about 80% of theory (1.0 g of AdoHcy per g of fresh beef liver).