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Bacteria of the genus Serratia, including a strain of Serratia liquifaciens isolated from contaminated porcine follicular fluid, produced an inhibitor of 125I-human follicle-stimulating hormone (hFSH) binding to calf testis membranes in vitro. In order to evaluate its potential usefulness and significance, we undertook studies to identify the site of action of this inhibitor. Large quantities (grams) of inhibitor-containing material (SL-1) were obtained by enrichment culture techniques and its chemical composition was determined. Follicle-stimulating hormone-binding inhibitory activity (FSH-BI) in SL-1 was associated with a protein-containing substance of approximately 30,000 Mr and also with larger Mr (greater than 300,000) forms. Preincubation studies demonstrated that binding inhibition by SL-1 was due to effects on the membranes rather than effects on the radioligand (125I-hFSH). Kinetics studies indicated that FSH inhibition by SL-1 was a relatively slow process that reached steady-state conditions between 23 and 25 h at 20 degrees C, in contrast to FSH, which reached steady-state conditions by 12 h at 20 degrees C. Estimates of FSH-BI activity, e.g., mass required to produce a 50% inhibition of 125I-hFSH binding, varied drastically when these kinetics differences were not taken into account. Our observations emphasize the need to establish steady-state conditions for each ligand before assessing mechanisms of action using Michaelis-Menton assumptions (e.g., competitive binding assays, Scatchard analyses).(ABSTRACT TRUNCATED AT 250 WORDS)

biology of reproduction

Follicle Stimulating Hormone Binding Inhibitor Produced by the Bacteria Serratia Interacts with Receptor for Follicle Stimulating Hormone in Calf Testis Membranes1