Q.: Why are most BIOLOG products sold in µmol and not in mg quantities? How much buffer is needed to achieve a 1 mM stock solution from a 5 µmol tube?

A.: We pack our products in micromol units in order to assist customers with the preparation of stock solutions. In contrast to often troublesome calculations regarding molecular weight, salt form, water content and purity percentages, simply add certain volumes of solvent (mostly water or buffer) and you already end up with stock solutions of defined concentrations. It's that easy!
If you need some assistance for calculating necessary volumes, click here please.

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Q.: I have successfully used several different cyclic nucleotide analogues in my biological system. However, I wonder if the different potencies observed could be partially due to different membrane permeability of the analogues?

A.: There are indeed huge differences in analogue lipophilicity within at least two magnitudes of order and your biological results will depend strongly on whether or not analogues are permeant for your system. BIOLOG has determined the lipophilicity of all its cyclic nucleotide analogues in order to allow a ranking with respect to membrane permeability. Please contact us for a ranking of the analogues you used.

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Q.: I recently heard that both dibutyryl cGMP and 8-bromo cGMP which are used rather frequently are not really recommendable as cGMP agonists. Which are the pitfalls and which substitutes do you suggest? (any references?)

A.: In dibutyryl cGMP mainly those functional groups (N² and 2') of the molecule are modified by butyryl groups which are essential for cGMP recognition at the kinase (cGK). While the 2'-butyryl group is split off by esterases, the second one remains. The resulting N²-monobutyryl-cGMP, however, is a very poor activator of cGK and even a better stimulator of cAMP-dependent protein kinase! In addition, the butyric acid released can disturb by own biological effects. 8-Bromo cGMP is indeed a good activator of cGK (in vitro). Due to its substitution with bromine it has better membrane permeability compared to cGMP, which is rather polar. However, this improvement is only relative: The membrane permeability of 8-Br-cGMP is only comparable to cyclic AMP which is still rather polar and impermeant. So rather high doses are usually necessary with intact cells in order to obtain reasonable effects. In addition, both compounds are not stable against PDE metabolism as often claimed. In fact, both compounds are hydrolyzed more slowly compared to cGMP. In our opinion, 8-(4-chlorophenylthio)-cGMP (8-pCPT-cGMP) is a good choice as a substitute. It has similar membrane permeability compared to dibutyryl cGMP, is metabolically stable and a powerful activator of all three cGK isozymes and of cGMP-gated ion channels, respectively. Reference: Geiger et al., PNAS, 89, 1031 - 1035 (1992).