INITIAL CHARACTERIZATION OF EQUINE INHIBIN

Inhibin has been characterized from a number of mammals; however, it h as not been extensively studied in horses. Western blot analysis was u sed to examine the size heterogeneity of equine inhibin alpha- and bet a-subunits. The distribution of equine inhibin activity from the initi al sizing column (S-200, 25 x 94 cm) indicated that the majority of eq uine inhibin activity was present as larger-molecular-size forms. When the large forms were analyzed by Western blot in nonreducing conditio ns, alpha-subunit bands were detected at 40 000 M(r), 56 000 M(r), 80 000 M(r), and 90 000 M(r); beta a reactive bands were identified at 56 000 M(r) (strong) and 90 000 M(r) (faint). Western blot analysis of t he lower-molecular-weight inhibins on one-dimensional (1D) SDS-PAGE ge ls revealed one inhibin band at 32 000 M(r). In reduced 1D-PAGE gels, a doublet alpha-subunit band was found at 18 000 M(r), and one beta a band was found at 14 000 M(r). The 18 000 M(r) equine alpha-subunit wa s present in three distinct spots in the isoelectric focusing (IEF) di mension of two-dimensional (2D)-PAGE, and closely overlapped those of porcine inhibin or-subunit. In conclusion, inhibin is present in good yield in equine follicular fluid. A higher proportion of the total act ivity is present in higher-molecular-weight forms than with porcine in hibin. Inhibin was detected at 90 000 M(r), 54 000 M(r), and 32 000 M( r). Alpha-subunit-only bands at 40 000 M(r) and 80 000 M(r) were detec ted. The lower-molecular-weight form of equine inhibin is similar to p orcine inhibin in size and pattern on 2D-PAGE.