Earlier we showed that using Os(VI) temed complex, glycans can be modified directly in glycoproteins and detected voltammetrically at mu M concentrations at carbon electrodes. Here we used Os(VI) 2,2'-bipyridine for modification of ribonucleases and Hg electrodes for voltammetric detection. We show that glycosylated RNase B produced electrocatalytic signal (after separation from the reaction mixture) at pM concentrations while non-glycosylated RNase A yielded negligible signal under the same conditions. Using Os(VI) temed and carbon electrodes voltammetric detection was less sensitive but allowed detection of RNase B in an excess of non-glycosylated protein, directly in the reaction mixture. We also showed that the constant current chronopotentiometric stripping (CPS) peak H (which is due to the ability of some amino acid residues in proteins to catalyze hydrogen evolution at Hg electrodes) could be used for protein structure-sensitive analysis at mercury electrodes. Using this peak, here we show that glycosylation of RNase stabilizes its molecule at the electrode. On the other hand, Os(VI) temed modification results in destabilization of this surface-attached protein. Peak H was also used for detection of RNase B separated from a large excess of non-glycosylated proteins on a lectin (concanavalin A) monolithic flow-through column. (C) 2017 Elsevier Ltd. All rights reserved.