Comparative Study on Monoclonal Immunoglobulin M and Rheumatoid Immunoglobulin M by Differential Scanning Microcalorimetry

I. I. Protasevich,¹ B. Ranjbar,¹ E. Yu. Varlamova,² I. A. Cherkasov,³ and V. A. Lapuk^3,4

¹Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow, 117984 Russia; fax: (095) 135-1405.

²Hematology Research Center, Russian Academy of Medical Sciences, Novozykovskii Proezd 4a, Moscow, 125167 Russia; fax: (095) 212-4252.

³Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii pr. 47, Moscow, 117913 Russia; fax: (095) 135-5328.

⁴To whom correspondence should be addressed.

Submitted March 19, 1997.

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Thermal denaturation of monoclonal immunoglobulin M (IgM) and rheumatoid immunoglobulin M (IgM-RF) and their Fab- and (Fc)₅-fragments was studied by differential scanning microcalorimetry. The melting of IgM-RF started at a higher temperature than that of IgM and the maximum temperature of its main asymmetric peak of heat absorption was higher by 4°C. At equal values of enthalpy, the thermal denaturation of IgM-RF and IgM consisted of four and five individual transitions, respectively, between pairs of states. The comparison of thermal denaturation parameters of Fab- and (Fc)₅-fragments of IgM-RF and IgM showed a thermodynamic similarity of (Fc)₅-fragments of both proteins, while their Fab-fragments differed in the interaction between V_L-C_L and V_H-C_H domains.

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KEY WORDS: rheumatoid immunoglobulin M, immunoglobulin M, Fab- and (Fc)₅-fragments, thermal denaturation, scanning microcalorimetry.

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