Protein! s molecular weight

Conversion of the relative ratios of amino acids into an estimate of actual composition requires some additional information concerning the protein s molecular weight for example, an analysis giving relative ratios of Ala (1.0), Gly (0.5), and Lys (2.0) could correspond to composition Ala2-Gly-Lys4 or any multiple thereof. The required information is usually available, and in any case, an estimation of composition based on a minimum molecular weight of the protein is always possible. 

Plotting the optical density as a function of the Calcofluor concentration yields a linear plot with a slope equal to the product (Is) (Figure 2.5). For a cuvette path length l equal to 1 cm, the slope is equal to s, expressed in mg-1 1 cm-1. Multiplying the value of e by the protein s molecular weight yields an e expressed in mM-1 cm-1. The value of s calculated from the slope is equal to 4.65443 g-11 cm-1 or 4387.76 M-1 cm-1. 

Polyacrylamide gel electrophoresis (PAGE) and high performance liquid chromatography (HPLC), which separate, detect, and quantify proteins present in a given system in a manner that also measures the protein s molecular weight, isoelectric point (p7) and other properties, are useful techniques in proteomic research. 

Fig. 2. Ultracentrifugal pattern for the water-extractable proteins of defatted soybean meal in pH 7.6, 0.5 ionic strength buffer. Numbers above peaks are approximate sedimentation coefficients in Svedberg units, S. Molecular weight ranges for the fractions are 2S, 8,000—50,000 7S, 100,000—180,000 IIS, 300,000—350,000 and 15S, 600,000—700,000 (9). The 15S fraction is a dimer of the IIS protein (10).

Homogenates of MetruUum senile, possibly the world s most common large sea anemone, yield extracts that are powerfully hemolytic for washed mammalian erythrocytes (22). The active substance, metridiolysin, is a protein of molecular weight approximately 80,000. In contrast to the sphingomyelin-inhibitable toxins, metridiolysin is an acidic protein having a pi of about 5. It is thermolabile and is inactivat by proteolytic enzymes. The optimal pH for hemolysis is between 5 and 6, and at pH 8 the lysin is inactive. It can be dissociated into two subunits of unequal size. Besides being cytolytic in vitro, metridiolysin is lethal when injected intravenously into mice. As shown in Table IV erythrocytes from the horse or dog are about a hundred times as sensitive to lysis as those from the mouse, and erythrocytes from other animals tested are intermediate in sensitivity. 

Smith, C.J.S., Slater, A. Grierson, D. (1986). Rapid appearance of an mRNA correlated with ethylene synthesis encoding a protein of molecular weight 35,000. Planta 168, 94-100. 

Despite its clever utility, SELDI suffers from several limitations. The SELDI MS instrumentation usually is capable of accurately detecting proteins with molecular weights less than 45,000, the detected proteins cannot be identified using this technique alone, and reproducibility in complicated experiments is suspect (86). Improvements in next-generation instruments using ProteinChip tandem MS techniques that enable direct protein identification (87), improved surface chemistries (88), and improved experimental design (89,90) should all greatly enhance SELDI s effectiveness as a powerful proteomic tool (91,92). 

There is, however, a further group of NADPH-dependent carbonyl reductases that transfer the 4-pro-S hydrogen [143]. These include human brain aldehyde reductase I [144], liver xenobiotic ketone reductase [145] and prostaglandin 9-ketoreductase [146], all monomeric proteins with molecular weights in the range of 30000-400000. 

This structural unit occurs in the one-iron proteins, rubredoxins (Rd), obtained from bacteria, in which the active site is [Fe(S-Cys)4], where S-Cys is a cysteinyl residue of the protein chain [structure (38) of Figure 6]. These proteins have molecular weights typically about 6000. The variety, of physical investigations (magnetic susceptibility,210 ESR,211 Mossbauer,212 optical absorption,207,213 MCD214) have demonstrated that the two redox states, Rdox and Rered, coupled by one-electron... 

The use of Schott s porous glass membremes (pore sizes from 10 to 90 nm) in the separation of proteins with molecular weights from 14,400 to 450,000 is illustrated by Langer and Schnabel [85] who show a decrease in retention with increasing pore size for different proteins. Due to the chemical nature of the membrane material, it lends itself to surface modifications, including the coupling of enzymes or the attachment of micro-organisms. 

---