A Surprising Message from Murines
Rat relaxin had been known for about 18 years and had been thoroughly characterized mainly through by Sherwood et al.1–4 The relaxin used in those studies had been isolated by the method of Walsh et al in which homogenized ovaries were extracted with a mixture of trifluoroacetic acid (15%), formic acid (5%), sodium chloride (1%) and hydrochloric acid (1M).5,6 The conditions seemed rather rough but an active hormone was obtained which was used for all subsequent studies until very recently. Rat relaxin (Fig.13.1), always considered to be a relaxin of low potency, made a natural connection to our structure function studies, in particular the beneficial effect of replacement of histidine B10 in insulaxin for a glutamic acid. In the rat this position was occupied by glycine and based on a central dogma in protein chemistry, this was an unfavorable situation. Glycine is considered a helix-breaking residue and its presence in the major B chain helix right at the receptor interaction site seemed a clear indication that glycine B14 was compromising the bioactivity of rat relaxin. The opportunity was irresistible to test one’s ability to predict how certain features in a molecule would influence its bioactivity and subsequently to improve on a natural product. First rat relaxin was needed to establish a baseline and consequently a few milligrams were synthesized by the new method.7
KeywordsPassive Immunization Protein Chemistry Human Relaxin Relaxin Receptor Crude Membrane Preparation
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