Proteins A and B form a covalent complex. Gel filtration shows a 200 kDa peak. SDS-PAGE with and without beta-mercaptoethanol shows single bands of 50 and 25 kDa, respectively. A has molecular weight 25 kDa. Find B molecular weight in kDa.
The official answer is 25 kDa. The intended interpretation is that reduction resolves the covalent subunits into equal 25 kDa chains, whereas nonreducing SDS-PAGE retains a 50 kDa disulfide-linked pair; a 200 kDa native assembly can contain four such pairs. Since A is 25 kDa, B is also 25 kDa. The printed “with and without … 50 and 25, respectively” reverses this ordinary reducing/nonreducing order. The source wording is preserved, but that inconsistency must be recognized rather than claiming reducing reagent normally increases subunit mass.
More Analytical tools: Electrophoresis, microarrays, enzymatic assays, immunoassays, immunoblotting, flow cytometry, whole genome and ChIP sequencing questions
GATE 2019 BT Q18– Which technique compares expression of many genes in two biological samples in a single…
GATE 2019 BT Q43– Hexapeptide P has pI 6.9. Variant Q replaces glutamate at position 3 with valine. They…
GATE 2025 BT Q55– Which of the following methods is/are used for identifying histone modifications?
GATE 2026 BT Q14– Cancer cells display a high level of heterogeneity in the expression of TP53 protein.…
GATE 2023 BT Q22– In ELISA, which of the following enzymes are conjugated to antibodies for detection of the…