For proteinisolation both BME and DTT are used, if BME was replaced by DTT the concentration of the latter would be reduced about 10 times. I don't know if this rule can be used here, but you may try depending on the complexity of your experiments.
In cell culture experiments, beta-mercaptoethanol is often replaced with alpha-thioglycerol. Alpha-thioglycerol is equally effective and more pleasant to work with. Recommended concentration: about 0.1 millimolar. See Exp. Hemat. 3: 32-43 (1975) for details.