Pitfalls in the differentiation of N-glycosylation variants of prostate-specific antigen using concanavalin A

We determined the optimal conditions for the separation of N-glycosylation variants of prostate-specific antigen using concanavalin A. Concanavalin A is a lectin that binds to the terminal sugar residues of glycoproteins. We demonstrated that differences in the percentage of prostate-specific antigen bound to concanavalin A-Sepharose in patients with benign prostatic hyperplasia compared with patients with prostatic carcinoma, as described in the literature, arise when insufficient concanavalin A binding sites are added for complete binding of the glycosylation variants of prostate-specific antigen. We observed similar percentages of prostate-specific antigen bound to concanavalin A-Sepharose for benign prostatic hyperplasia (86.3% +/- 7.5, mean +/- SD) and carcinoma patients (81.8% +/- 12.0, mean +/- SD), when sufficient concanavalin A-Sepharose was added to allow optimal binding, and when samples with high prostate-specific antigen concentrations were not pre-diluted before incubation with concanavalin A-Sepharose. We conclude that differentiation of patients with benign prostatic hyperplasia or carcinoma of the prostate on the basis of differences in percentages of prostate-specific antigen bound to concanavalin A-Sepharose, i.e. separation of N-glycosylation variants, is not possible.