# Why do Bence-Jones proteins behave differently in urine heat test?

The preliminary test for proteinuria (proteins in urine) is precipitation/turbidity on heat due to denaturation. This turbidity should not disappear when 10% acetic acid is added - to differentiate from phosphates. Bence-Jones proteinuria is found in multiple myeloma and they are light chains of IgG and are definitely proteins! They have this unusual behaviour, i quote,

Bence-Jones proteins are light chains of γ-globulin. These are excreted in multiple myeloma and other parapro- teinaemias. In heat and acetic acid test performed under temperature control, these proteins are precipitated at lower temperature ($\mathrm{56\ ^\circ C}$) and disappear on further heating above $\mathrm{90\ ^\circ C}$ but reappear on cooling to lower temperature again.

How is this behaviour explained?

• What's the source of quote? – Mithoron Jul 26 '16 at 17:38