Activity of alkylated prolactin and human growth hormone in receptor and cell assays.
The disulfide bonds of two lactogenic hormones, ovine prolactin (oPRL) and human growth hormone (hGH), were reduced with dithiothreitol under denaturing conditions and alkylated with iodoacetic acid. The modified hormones were assayed for their ability to bind the plasma membrane-bound receptor for lactogenic hormone found in the rabbit mammary gland. S-Carboxymethylated ovine prolactin (SCM-oPRL) with all six cysteine residues modified had a nearly 300-fold decrease in binding as compared to native oPRL in a competitive binding assay using [125I]ovine prolactin. The S-carboxymethylated human growth hormone (SCM-hGH) had all four of its cysteine residues modified. It showed only a slightly reduced ability to bind the rabbit mammary gland prolactin receptor in a competitive binding assay with [125I]ovine prolactin. The two modified hormones were assayed for their ability to stimulate proliferation of the lactogen-dependent Nb 2 lymphoma cell line. SCM-oPRL required concentrations greater than 1 X 10(5) that of native oPRL to stimulate 50% of the maximum cell growth. SCM-hGH retained a significant amount of its ability to stimulate the Nb 2 lymphoma cells.
Necessary
P C
PC
Andersen
T T
TT
Ebner
K E
KE
D000478:Alkylation; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002460:Cell Line; D002942:Circular Dichroism; D004229:Dithiothreitol / Q000494:pharmacology; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D006801:Humans; D007461:Iodoacetates; D019807:Iodoacetic Acid; D008223:Lymphoma / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000378:metabolism; D011388:Prolactin / Q000494:pharmacology*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011981:Receptors, Prolactin
D000596:Amino Acids; D007461:Iodoacetates; D011956:Receptors, Cell Surface; D011981:Receptors, Prolactin; D011388:Prolactin; D013006:Growth Hormone; D004229:Dithiothreitol; D019807:Iodoacetic Acid