Genetic Variation of the Equine Serum Protease Inhibitor System Pi (Pr) Characterized By an Enzyme Binding Staining Technique After Starch Gel Electrophoresis

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Abstract
A modification of Uriel & Berges (1968) staining technique has been developed for starch gels. This method, which makes use of the Pi proteins ability to bind trypsin and chymotrypsin, allows for the recognition of the Pi zones which migrate into slower positions than originally described by Braend (1970). The Pi zones appear as white bands against a lilac background. Serum samples from 18 sire families selected according to the Pi type of the sires have been studied. Ten families were Norwegian Trotter, 8 were Warm-blood Trotter (Standardbred). In each family 12 dam-offspring pairs were examined. In trypsin-treated gels the white zones usually correspond to those previously recognized by protein-staining. In addition, the products of the PiG, Pi1, PiL and PiW alleles each had 1 distinct slow band, but in different positions. The products of the PiN and PiU alleles lacked slow zones. The Pis and PiT alleles differed with respect to the positions of their slow bands. A new allele PiT1 was identified. This has a slow band in a different position from that of the PiL allele. An allele indistinguishable from PiZ was recognized in Norwegian Trotter in which also a new alle Je temporarily called PiY could be demonstrated. In chymotrypsin-treated gels the zone patterns of some of the allele products differed from those seen after trypsin-treatment.