CL (Compatible Lowry) Protein Assay

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SKU: 786-1077-XX Category:
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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%
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
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%
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
  • Protein quantitation in the presence of detergents and reducing agents
  • Quick 15 minute incubation
  • Increased color stability (color will not change more than 5% in 1 hour or 10% in 2 hours)
  • Linear response 0.2 – 1.5 mg/ml
  • One simple protocol without cumbersome sample preparation or buffer exchange steps
  • Convenient kit provides all necessary reagents for 250 standard (5ml) assays or 1000 microtube (1.5-2 ml) assays
  • Estimate protein during protein purification, electrophoresis, cell biology, molecular biology, and other research applications.
  • Suitable for protein samples containing common laboratory agents, such as reducing agents, chelating agents (EDTA), detergents, amines (Tris), sugars and many other agents.
  • Suitable for samples containing chaotropic agents such as urea, thiourea, guanidine hydrochloride, guanidine thiocyanate, ammonium sulfate, drugs, antibiotics, cobalt, and numerous other agents and extraction buffers.
  • Suitable for determination of protein concentration in cellular fractions, tissue & cell lysates and chromatography purification fractions.

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