The stability of immunological and biological activity of human thyrotropin in buffer: its temperature-dependent dissociation into subunits during freezing

Abstract

The stability of thyroid-stimulating hormone (TSH) in buffer under various storage conditions was studied with regard to its immunoreactivity measured by an immunoradiometric assay and its bioactivity by a sensitive FRTL-5 cell bioassay. The immunoreactivity was well retained at 4 °C or 24 °C throughout the study period of 90 days. At –20 °C, however, it decreased proportionately with the storage time. The mean reduction was 42.1% at 90 days compared with that when stored at –80 °C. The bioactivity showed a similar course of change with its reduction of 44.3% at –20 °C in 90 days. The loss of both activities was attributed to the dissociation of human (h)TSH molecule into its subunits. The concentration of the a subunit of hTSH in those samples stored at –20 °C gradually increased from the initial undetectable level to that almost equivalent on a molar basis to the loss of immunoreactivity. The enrichment of albumin in the buffer to a level of more than 1.0% was effective in preventing the occurrence of such a phenomenon. These data indicate that hTSH, when frozen at –20°C in buffer is gradually dissociated into its subunits, despite its outstanding stability for 90 days at both 4 °C and 24 °C. However, no apparent inconsistency between immunological and biological activities, was observed at any temperature between -20 °C and 24 °C.

Key Words:

• Key-words
• bioactivity
• temperature stability
• thyrotropin