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MDK · Western blot design guide
Design a Western Blot for MDK
Real validated MDK Western blot protocols, expected-band and isoform facts, troubleshooting for weak or shifted signal, and recommended anti-MDK WB antibodies. Everything you need to plan the experiment before you commit precious samples.
Last reviewed: May 2026 · Scientific review: Boster Bio technical team
MDK Western Blot Experimental Design Guide
Expected bands, validated protocols, controls and antibodies — the at-a-glance facts below, then the full design guide.
Must know before running
| Expected band | ~15.6 kDa | |
| Observed band | ~16 kDa | |
| Gel | 12–15% | |
| Positive control | Adipose tissue+4 more · see all | |
| Negative control | Adipose tissue+4 more · see all |
Important caveats
Reasons your observed band may differ from the expected size.
| PTM | Cleaved | |
| Caveat | Signal peptide cleavage | |
| Regulation | Estrogen up | |
| Isoform | 2 isoform(s) |
Section 1
Real Curated MDK Western Blot Protocols
Literature-validated Western blot parameters for MDK — gel percentage, transfer, blocking, antibody incubation and detection, extracted from published methods.
| Sample / lysate | human SH-SY5Y , Lane 2: human U20S . After electrophoresis, proteins were transferred to a nitrocellulose membrane at 150 mA for 50-90 minutes. Blocked the membrane with 5% non-fat milk/TBS for 1.5 hour at RT. The membrane was incubated with rabbit anti-MDK antigen affinity purified polyclonal antibody (Catalog # RP1051) at 0.5 μg/mL overnight at 4°C, then washed with TBS-0.1%Tween 3 times with 5 minutes each and probed with a goat anti-rabbit IgG-HRP secondary antibody at a dilution of 1:5000 for 1.5 hour at RT. The signal is developed using an Enhanced Chemiluminescent detection (ECL) kit (Catalog # EK1002) with Tanon 5200 system. A specific band was detected for MDK at approximately 16 kDa. The expected band size for MDK is at 16 kDa |
| Gel % | 12–15% |
| Load | 30 ug |
| Transfer | nitrocellulose membrane, 150 mA, 50–90 min |
| Membrane | nitrocellulose |
| Blocking | 5% non-fat milk / TBS, 1.5 h RT |
| Primary antibody | 0.5 µg/mL |
| Primary incubation | overnight at 4 °C |
| Secondary antibody | goat anti-rabbit IgG-HRP, 1:5000 |
| Wash | TBS-0.1% Tween, 3 × 5 min |
| Detection | ECL |
| Exposure / imaging | Tanon 5200 |
| Observed band | 16 kDa |
Section 2
What Is the Expected MDK Western Blot Band Size?
MDK (midkine) is a 15.6 kDa predicted monomer that runs near its observed ~16 kDa band, since it is non-glycosylated with intrachain disulfide bonds.
| Single band near 15-16 kDa | Non-glycosylated, mature monomeric midkine running close to its 15.6 kDa predicted mass |
| Little or no band in whole-cell lysate | Midkine is a secreted extracellular growth factor, so most of it is exported rather than retained intracellularly |
| Faint band near roughly double the monomer mass under non-reducing conditions | Midkine's annotated homodimer partially persisting before complete denaturation/reduction |
| Two closely spaced bands near the main band | The two annotated splice isoforms (1 and 2) migrating at slightly different apparent masses |
| Slight band shift between reduced and non-reduced lanes | The five disulfide bonds hold the chain in a compact fold that migrates differently until fully reduced |
| Band slightly smaller than the full 143-residue sequence would predict | Cleavage of the 20-residue N-terminal signal peptide to generate the secreted mature chain |
💡Expected MDK appearanceExpect a single sharp band at ~16 kDa in conditioned media/secretome samples, closely matching the 15.6 kDa predicted mass of non-glycosylated, signal peptide-cleaved mature midkine, with little to no signal in whole-cell lysate.
| Predicted mass (UniProt) | Sets the ~15.6 kDa baseline migration for the non-glycosylated monomer, matching the ~16 kDa band commonly observed |
| Signal peptide cleavage (residues 1-20) | Removes the N-terminal signal sequence so the secreted mature chain runs slightly smaller than the unprocessed 143-aa precursor |
| Five intrachain disulfide bonds | Compact disulfide-stabilized folding can shift migration between non-reduced and fully reduced samples relative to the linear predicted size |
| Homodimer formation | Can produce a fainter higher-mass band under non-reducing or incompletely denaturing conditions, though the dimer typically dissociates to monomer under standard reducing SDS-PAGE |
| Alternative splicing (isoforms 1 and 2) | The two annotated isoforms can appear as an extra band close to the main monomer band rather than a single uniform species |
| Situation | Likely cause | Next action |
|---|---|---|
| No band in lysate | Midkine is a secreted growth factor that is exported from the cell, so whole-cell lysate may contain little of the mature protein | Test conditioned media or serum-free culture supernatant alongside or instead of whole-cell lysate |
| Band higher than expected | Incomplete reduction lets the non-covalent homodimer or disulfide-stabilized conformers persist | Increase reducing agent (DTT/BME) concentration and boil the sample longer before loading |
| Multiple bands | The two annotated splice isoforms plus residual monomer/dimer equilibrium can produce more than one band | Run reducing and non-reducing gels side by side and compare positions to distinguish isoform bands from oligomeric species |
| Weak or no signal | Midkine is a small, low-abundance secreted growth factor that can run off small-format gels or transfer poorly | Use a higher-percentage gel (12-15%) with a low-MW transfer protocol and concentrate conditioned media before loading |
| Fragments below expected size | The compact fold held together by five disulfide bonds can be nicked or partially reduced during sample handling, releasing smaller fragments | Keep samples cold, add protease inhibitors, and avoid excessive heating or reducing conditions during preparation |
Experiment evidence
Western blot images showing MDK band
RP1051 · MDK
← swipe / scroll for more images →
Real WB data behind the band-size expectations in this section.
Sample controls for MDK Western blot
🧪For positive controls for MDK in Western blot, you can use conditioned medium or cell lysate from an MDK-overexpressing/secreting cell line, since none of the profiled HPA tissues (adipose tissue, adrenal gland, appendix, bone marrow) register detectable expression to serve as a natural positive tissue.
Positive control: Conditioned medium (MDK-secreting cell line)
Negative control: Adipose tissue
Loading controls: Run GAPDH and β-actin blots alongside a total-protein stain (e.g., stain-free gel, Ponceau S, or REVERT) as loading controls.
⚠️Feasibility: MDK is secreted, so whole-cell lysates give weak signal and conditioned medium/concentrated supernatant is needed for a reliable positive control, while the available HPA tissues only report 'Not detected' with no confirmed high-expressing reference to validate specificity against.
HPA tissue expression evidence for MDK
Comprehensive Human Protein Atlas IHC scoring per tissue. Rows are taken directly from the HPA tissue chart — click any row's HPA link to view the source.
Positive expression · recommended positive controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Adipose tissue | adipocytes | Not detected | Protein (IHC) | HPA → |
| Adrenal gland | glandular cells | Not detected | Protein (IHC) | HPA → |
| Appendix | glandular cells | Not detected | Protein (IHC) | HPA → |
| Bone marrow | hematopoietic cells | Not detected | Protein (IHC) | HPA → |
| Breast | adipocytes | Not detected | Protein (IHC) | HPA → |
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Adipose tissue | adipocytes | Not detected | Protein (IHC) | HPA → |
| Adrenal gland | glandular cells | Not detected | Protein (IHC) | HPA → |
| Appendix | glandular cells | Not detected | Protein (IHC) | HPA → |
| Bone marrow | hematopoietic cells | Not detected | Protein (IHC) | HPA → |
| Breast | adipocytes | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced MDK Western Blot Tips
Deeper troubleshooting and optimisation questions for MDK, answered from its protein features.
Why does MDK run close to its predicted 15.6 kDa mass?
MDK has no glycosylation or modified residues, and its residues 1-20 signal peptide is cleaved before secretion, leaving a small mature core stabilized by 5 disulfide bonds. With no added PTM mass, the observed ~16 kDa band matches the predicted mass closely, unlike many glycoproteins that shift upward on gels.
Could MDK isoforms cause an extra WB band?
UniProt lists two MDK isoforms arising from alternative splicing. A minor size difference between isoform 1 and isoform 2 could appear as a faint secondary band near the main ~16 kDa signal. If a doublet appears, confirm identity with an isoform-specific antibody or sequence mapping rather than assuming degradation.
Is MDK expression induced under certain conditions?
MDK is a developmental growth factor linked to cell differentiation, with expression rising during embryonic development and in tissue injury or hypoxic stress responses, consistent with its growth factor and differentiation-associated keywords. Use a known inducing condition, such as differentiation induction or hypoxic culture, as a positive control for antibody performance.
How should blocking be optimized for MDK detection?
MDK is a heparin-binding secreted protein, so its basic heparin-binding surface can bind nonspecifically to membranes and blocking proteins. Use BSA-based rather than milk-based blocking to reduce this electrostatic background and improve signal-to-noise around the ~16 kDa band.
What transfer method to use for MDK Western blot?
MDK is a small (~15.6 kDa) secreted protein, so use a 0.2 micron PVDF or nitrocellulose membrane, reduced methanol content, and a short semi-dry or wet transfer time to prevent blow-through. Its compact, disulfide-stabilized structure transfers efficiently under standard low-molecular-weight protein conditions.
Do reducing conditions affect MDK quantitation?
MDK forms homodimers and contains 5 disulfide bonds, so incompletely reduced samples can retain dimer or multimer species migrating near 30-32 kDa instead of the ~16 kDa monomer. For accurate quantitation, always run samples under fully reducing conditions with DTT or beta-mercaptoethanol before loading.
What explains higher-molecular-weight MDK bands?
Incomplete reduction of MDK's 5 disulfide bonds or homodimer formation can leave species migrating above the ~16 kDa monomer, often near 30-32 kDa. Since MDK carries no glycosylation to explain a shift, treat persistent higher bands as dimer or incomplete-reduction artifacts rather than novel proteoforms.
Boster reagents
Best MDK Western Blot Antibodies
BosterBio's MDK antibodies are among the best-performing WB antibodies on the market — well cited, thoroughly validated, and orthogonally cross-validated against negative tissues and complementary methods.
Real WB data
Anti-Midkine/MDK Antibody Picoband®
Cat # RP1051
Our recommended anti-MDK antibody delivers top-tier Western blot performance, backed by extensive citation history and rigorous validation, including orthogonal confirmation against negative tissue controls and complementary detection methods for dependable, reproducible results.
Which to pick: Only one anti-MDK antibody is catalogued here: RP1051. It includes a genuine Western blot validation image on SDS-PAGE, making it the clear, and currently only, choice for MDK detection in your blot.
Source: BosterBio MDK gene-info card — filtered to Western-blot-capable antibodies; each card shows that product's actual WB validation figure.
References
- UniProt Consortium. UniProt entry P21741.
- Human Protein Atlas. MDK tissue expression.