Evolution ofNeurophysin Proteins: ThePartial Sequence ofBovineNeurophysin-I

The sequenceofthefirst 50amino-acid residues ofbovineneurophysin-I wasdetermined. A com- parison ofthissequencewiththatofthe97-residue bovine neurophysin-Il andthe92-residue porcineneurophysin-I molecules reveals ahighdegreeofhomologyamongthese proteins. Itissuggested thatthebindingsiteofneurophy- sinproteins forneurohypophyseal hormonesislocated inthemiddleportionofthesemolecules, wheretheirse- quencesarevirtually identical. Thesequencedata,aswell astheoccurrence ofatleast twoneurophysins inboththe pigandthecow,suggest thateachspecies inherited atleast twostructural genescontrolling thesynthesis ofthesepro- teins. Themoststriking finding inthestudywastheob- servationofinternalsequencehomologieswithinthe neurophysins. Thisresultimpliesthatthesemolecules arosebywayofa series ofpartial geneduplications ofa primitive genethatcodedforasmaller ancestral protein. VanDykeetal.(1)isolated frombovine posterior pituitary glands theneurohypophyseal hormones, vasopressin and oxytocin, asnoncovalent complexes withcertain protein molecules. Theprotein components werelatergiventhe generic nameneurophysins (2), andtheyareconsidered to function ascarrier substances towhichtheneurohypophyseal hormones areboundduring transport andstorage within the