Molecular weight determination by sedimentation equilibrium

The heat stability of glutaminase-asparaginase modified with glu-taraldehyde-activated glycopeptides was slightly greater than that of the native enzyme, as was its susceptibility to trypsin.108 This modification decreased the pi by several pH units, and altered the association behavior the glycosylated enzyme had a much wider distribution of molecular weights as determined by sedimentation equilibrium. 

Calculated from the amino acid composition. The molecular weights were calculated from sedimentation and difiiision measurements, unless otherwise stated. Determined by sedimentation equilibrium studies. Determined by light-scattering. Value from osmotic-pressure measurements, 15,400. minimum value determined by gel permeation. Value from osmotic-pressure measurements, 59,500. Extrapolated from published data. 

Figure 3 a) Molecular weight determination by equilibrium ultracentrifugation b) Comparison of molecular weights determined by the Archibald method and by sedimentation equilibrium. 

Molecular weight has been determined in several ways, the most commonly employed being determination by sedimentation equilibrium. In general, the molecular weight of human erythrocuprein is reported to be 33,600 (60) and the corresponding value for bovine erythrocuprein 32,600 (70). These values can be considered identical since they are within the experimental error. A summary of different determinations is given in Table 1. 

Transacetylase monomer has a molecular weight of 29,700 as determined by sedimentation equilibrium in 6 Af guanidinium chloride and usually exists as a dimer [86]. The enzyme has a carboxyl terminus of valine, but studies to determine the amino terminal amino acid have shown heterogeneity and no true assignment can be made [87]. Transacetylase has been crystallized from induced cells where it has been found to account for up to 0.3 % of the cellular protein [88]. 

Human RBP has a molecular weight of 21,200 (Peterson, 1971a) to 21,300 (Raz et al., 1970), as determined by sedimentation equilibrium analysis in the analytical ultracentrifuge. The molecular weight calculated from the reported... 

This chapter contains one of the more diverse assortments of topics of any chapter in the volume. In it we discuss the viscosity of polymer solutions, especially the intrinsic viscosity the diffusion and sedimentation behavior of polymers, including the equilibrium between the two and the analysis of polymers by gel permeation chromatography (GPC). At first glance these seem to be rather unrelated topics, but features they all share are a dependence on the spatial extension of the molecules in solution and applicability to molecular weight determination. 

The molecular weight of a protein can be determined by SDS-polyacrylamide gel electrophoresis or by sedimentation equilibrium. Which method would you use to determine the molecular weight of a protein containing four subunits, each consisting of two polypeptide chains cross-linked by two disulfide bridges Explain your answer. 

Na-K ATPase is composed of two different subunits, one of about 100000 (a-subunit) and one of about 50000 (yS-subunit), as shown by sodium dodecyl-sulfate (SDS) gel electrophoresis [75,76]. Since both subunits are glycoproteins and therefore bind different amounts of SDS as compared to normal proteins, their SDS gel electrophoretic mobility, and hence their apparent molecular weights can deviate considerably. Recently the molecular weights of the separated subunits of Na-K ATPase from rabbit kidney outer medulla have been determined more accurately by sedimentation equilibrium analysis in the absence of detergents [77]. The value for the a-subunit thus determined is 131000 (120600 for its protein part) and 61 800 for the /8-subunit (42 800 for its protein part). 

The molecular weight of transketolase from baker s yeast has already been determined by Datta and Racker [9] who found a molecular weight of 140000 in the analytical ultracentrifuge. We could confirm this value of 140000 by sedimentation equilibrium runs [8]. 

G(S), and crosslinking, G(X), from measurements of average molecular weights is extended by utilizing. It is useful to determine and simultaneously by sedimentation equilibrium in the ultracentrifuge. 

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