ABSTRACT
During the last 10 years there has been increasing awareness of molecular heterogeneity of a number of hormones, including luteinizing hormone (LH). During the 1950s and I 960s many investigators were primarily concerned with isolation and purification of hormones using, for the most part, rather crude fractionation systems. Human pituitary glands obtained at autopsy were preserved frozen or acetone-dried and subsequently extracted. Purification often comprised ammonium sulfate or ethanol fractionation followed by various ion exchange chromatography steps. 1-8 Many investigators were not aware of the need to include protease inhibitors from the very beginning of the procedure. Consequently, when characterization of the highly purified preparations by electrophoresis or isoelectric focusing revealed a multitude of protein bands, this was later interpreted as being purification artifacts.9-lo
However, during the 1970s, immunoassay systems with ever-increasing specificity and sensitivity became available. Hence it was possible to assess the immunoreactive profile after isoelectric focusing of gently extracted single pituitary glands or even plasma samples. The observations in such cases of a variety of molecular forms gradually led to the conclusion that there exists a "natural" heterogeneity, at least for LH and the other pituitary glycoprotein hormones, follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH).
