Assay kits that measure enzyme activity and metabolite levels in tissue, cells, serum and plant samples, and cell function products for viability, proliferation, apoptosis and cell cycle experiments.
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| Group | Examples | Typical readout |
|---|---|---|
| Enzyme activity | Succinate dehydrogenase, pyruvate dehydrogenase, hexokinase, pyruvate kinase, alpha-galactosidase, alanine aminotransferase (ALT, SGPT) | Absorbance change per minute |
| Metabolites | Free fatty acids, proline, glutamic acid | Endpoint absorbance against a standard |
| Antioxidant capacity | DPPH, ABTS and hydroxyl radical scavenging | Loss of colour at 517 or 734 nm |
| Viability and proliferation | MTT and WST-8 (CCK-8 type) assays | Formazan absorbance |
| Apoptosis and staining | Acridine orange and propidium iodide based kits | Fluorescence microscopy or flow cytometry |
| Cell cycle | Propidium iodide DNA content kits | Flow cytometry |
Most enzyme reactions are invisible, so kits couple them to something a plate reader can see. There are three common ways:
The enzyme activity assay guide lists the reaction and readout for common kits, and the SDH assay guide works through one assay from sample to units.
| Assay | Measures | Readout | Keep in mind |
|---|---|---|---|
| MTT | NAD(P)H-dependent metabolic activity | Purple formazan at 570 nm after solubilising | Endpoint; the cells cannot be reused |
| WST-8 (CCK-8 type) | Metabolic activity | Water-soluble formazan at 450 nm | No solubilising step; gentler on cells |
| Acridine orange staining | Membrane integrity and nuclear morphology | Green live cells; red-orange dead cells with PI or EB | Microscopy or flow cytometry |
| Propidium iodide cell cycle | DNA content per cell | G0/G1, S and G2/M peaks | Fixed cells, RNase treatment needed |
Metabolic assays report metabolism, not cell number. The MTT vs CCK-8 guide explains when that difference matters and how to choose.
Enzymes lose activity once they leave the cell. Work on ice, homogenise in a non-denaturing buffer and assay the same day where you can. Strong detergents, metal chelators such as EDTA (for metal-dependent enzymes) and reducing agents can all change the result, so use the buffer the manual specifies.
Normalise activity to total protein measured with a compatible protein assay. The lysis buffer guide explains which buffers keep proteins native.
To link activity to protein levels, pair these kits with ELISA kits or antibodies for the same target.
Usually the amount of enzyme that converts one micromole of substrate per minute under the assay conditions. Kits often report activity per milligram of protein, per gram of tissue or per millilitre of sample, so check the definition in the manual before comparing numbers.
Activity declines after collection, so assay fresh samples where you can. If you must store them, snap-freeze in liquid nitrogen, keep at -80 °C and avoid repeated thawing. Test a stored and a fresh sample side by side once to see how much activity you lose.
Only for kits read at 340 nm, which follow NADH or NADPH directly. They need a reader that measures at 340 nm and UV-transparent plates or cuvettes. Many kits use dyes read in visible light instead.
CCK-8 type (WST-8) assays need no solubilising step, are less toxic to cells and allow further culture after reading. MTT is cheaper and well established. Both measure metabolic activity rather than cell number.
Many enzyme and metabolite kits include protocols for plant tissue, and soil enzyme kits are designed for soil. Send us your sample type and we confirm the kit's manual covers it.
Biochemical and cell assays
Succinate dehydrogenase is the only enzyme in both the Krebs cycle and the electron transport chain, which makes its activity a direct read on mitochondrial function. Here is how the assay works and how to get numbers you can trust.
5 minute read
Biochemical and cell assays
Most enzyme activity kits turn a reaction you cannot see into a colour change you can measure. Once you know the two or three ways they do it, choosing a kit and reading the result gets much easier.
4 minute read
Biochemical and cell assays
Viability assays measure metabolism, membranes or ATP, never cell number directly. Knowing which one you are measuring explains most odd results and tells you which assay to pick.
5 minute read
Biochemical and cell assays
Many strange MTT results come from the compound reducing the dye, or from formazan crystals lost during aspiration. One cell-free blank and a seeding curve catch most of them.
3 minute read
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