The long-term objective is to isolate and characterize the structural variants of growth hormone and prolactin that are found in the pituitary gland and placenta. Our hypothesis is that each of these protein hormones exist as a complex of different forms which is responsible for their multiple activities. Our first priority is the structure analysis of two forms of human growth hormone that have more alkaline isoelectric points than the major form of the hormone (hGH). We have special interest in one of the forms because it has greater lactogenic activity than hGH. The variants are extemely difficult to separate from hGH, electrophoretic techniques being the only way we have been able to resolve them. Preparative isoelectric focusing offers a possible technique for their isolation on a relatively large scale.
Our second aim i s to determine if bovine pituitary glands contain a variant that corresponds to the 20,000-dalton form of hGH (hGH2OK). This substance appears to be a product of altered m-RNA splicing. A substance with this molecular weight has been detected by electrophoretic analysis of bovine pituitary extracts, but we must now isolate and characterize the component. Isolation of a bovine GH20K would indicate a more general importance for the variant. We will continue to supply investigators with hGH20K.
The third aim i s to isolate and characterize a 25K-dalton component that we have detected in preparations of bovine prolactin (23K). The substance appears to be a variant of prolactin, so it will be important to learn its physiologic actions.
The fourth aim i s to study the multiple forms of human placental lactogen to determine how they differ structurally and biologically. Isolation procedures include chromatography on Sephadex and DEAE-cellulose, preparative gel electrophoresis and isoelectric focusing. Amino acid sequencing will be done on tryptic peptides isolated by HPLC. Several genes for growth hormone have been identified but it is not known whether the genes are normally expressed. These studies will help answer this and in addition, characterization of the variants will provide information on significance of the multiple forms of growth hormone, prolactin and the placental lactogen.
