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G-Biosciences’ CL (Compatible Lowry) Protein Assay is based on the widely cited protein assay by Lowry et. al. (1951). The CL Protein Assay improves upon the traditional Lowry method to be compatible with common laboratory agents known to interfere with Lowry protein assays such as reducing agents (dithiothreitol (DTT), ß-mercaptoethanol and TCEP), detergents, chelating agents, amines, sugars, strong chaotropic buffers, salts, drugs, antibiotics, cobalt and other common laboratory agents (see tables 1 and 2). The CL Protein Assay uses G-Biosciences’ proprietary Universal Protein Precipitating Agent (UPPA™). The UPPA agent cleans the protein samples from interfering agents prior to performing colorimetric reaction. The assay is supplied with either traditional bovine serum albumin (BSA) protein standard, pre-diluted BSA protein standards, non animal protein standard or bovine ɣ globulin protein standard.
A ML (Modified Lowry) Protein Assay is available for detergent containing samples without reducing agents. The ML Protein Assay is compatible with a wide variety of detergents used in protein research in addition to other common reagents such as EDTA and Tris (see tables 1 and 2).
Table-1: A selection of compounds and their maximum concentrations compatible with the ML and CL Protein Assay.
Reagent | ML Protein Assay | CL Protein Assay |
---|---|---|
Amino Acids | Compatible | - |
Ammonium Sulfate | 0.5M | 40% |
β-Mercaptoethanol | X | 5%, 15%* |
Brij® 35 | 1% | 1% |
Calcium Chloride | 0.05M | - |
CHAPS | 1% | 4% |
CHAPSO | 1% | 1% |
CTAB | - | 1M |
Deoxycholate | 1% | - |
Digitonin | 0.3% | - |
DTT | 0.001M | 0.1M, 0.35M* |
EDTA | 0.025M | 0.1M |
Glycerol | - | 30% |
Guanidine.HCl | 0.4M | 6M |
Guanidine Thiocynate | - | 6M |
HEPES | - | 0.1M |
Hydrochloric Acid | 0.5M | - |
Imidazole | - | 0.5M |
Iodoacetamide | - | 15mM |
Laemmli Buffer (w/5% β-Mercaptoethanol) | - | Compatible |
NP-40 | 2% | - |
Octaethyleneglycol dodecyl ether | 0.2% | - |
Octyl Glucoside | 1% | - |
Phosphate Buffer | - | 0.2M |
Sarcosyl | - | 1% |
SDS | 10% | - |
Sodium Azide | 0.05% | 0.1M |
Sodium Chloride | - | 0.5M |
Sodium Hydroxide | 0.5M | 2.5M |
Sucrose | - | 30% |
TCEP | - | 15mM |
Thesit® | 1% | 2% |
Thiourea | - | 2M |
Tributylphosphine (TBP) | 0.002M | - |
Tris (pH 8) | 0.1M | 0.5M |
Triton® X-100 | 1% | 3% |
Triton® X-114 | 1% | 3% |
Tween® 20 | 1% | 2% |
Urea | 4M | 8M |
Zwittergent® 3-12 | - | 1.5M |
-, not tested; X, not compatible; *, two washes (optional).
Table 2: ML & CL Protein Assay are compatible with strong chaotropic extraction buffers
Buffer Composition |
4M Urea, 1% SDS, 10mM EDTA, 0.8% β-Mercaptoethanol |
6M Urea, 2M Thiourea, 4% CHAPS |
6M Urea, 2M Thiourea, 4% NP-40 |
1% Sarcosyl, 0.8 β-Mercaptoethanol, 4M Guanidine Thiocyanate, 10mM EDTA |
6M Urea, 2M Thiourea, 2% CHAPS, 2% ND SB 201 |
6M Urea, 2M Thiourea, 2% CHAPS, 2% SB 2 10 |