Microheterogeneity of equine follicle-stimulating hormone

The present report demonstrates the microheterogeneity of equine follicle-stimulating hormone (eFSH), and its subunits, and characterizes eFSH isoforms with respect to receptor-binding and immunological properties. The isoelectric microheterogeneity of eFSH was demonstrated by the isolation of two highly purified hormone preparations (eFSH-A and eFSH-B) from different cation-exchange chromatography fractions (Sephadex SP-C50). Equine FSH-A eluted before eFSH-B, indicating a greater apparent negative charge. This apparent charge difference was substantiated by subsequent analysis by chromatofocusing. These two hormone preparations were then analyzed by FSH radioreceptor assay (RRA) and eFSH radioimmunoassay (RIA). The FSH receptor-binding/immunological activity (RRA/I) ratio of eFSH-A was significantly greater than that of eFSH-B (p less than 0.05). No significant differences between the two FSH preparations were detected by RIA. To study eFSH microheterogeneity in more detail, a standard eFSH preparation was analyzed by the technique of chromatofocusing. A variety of immunoreactive forms were observed in the range of pH 7 to 14, with a large amount of material eluting at less than pH 4.0. Chromatofocusing fractions corresponding to pI values of 6.6, 6.4, 5.8, 5.5, 5.2, 4.8, 4.6, 4.3, 4.1, and less than 4.0 were analyzed by RRA and RIA. The respective RRA/I ratio values were 0.35, 0.61, 0.82, 1.16, 1.23, 1.70, 1.73, 1.46, 1.09, and 1.55. Values that differ by more than 0.2 are significantly different (p less than 0.05, Student-Newman-Keuls multiple comparison). This is in agreement with the data obtained with eFSH-A and -B, which showed the more negatively charged preparation possessed the higher RRA/I activity ratio.(ABSTRACT TRUNCATED AT 250 WORDS)