Teh H. Lee

The Melanocyte-Stimulating Hormones

Publisher Summary From a research standpoint the subject of hormonal control of pigmentation is only forty-six years old. It began when two biologists, P. E. Smith and B. M. Allen independently and at the same time, found that removing the pituitary glands of tadpoles and frogs produced marked lightening in the color of their skin. During the forty years following these initial observations, intense interest, developed in this field, particularly among biologists. Attempts were made to learn how endocrine and neurogenic factors controlled darkening and lightening of melanocytes. During the last six years a great effort has been made by biochemists to isolate, characterize, synthesize, and evaluate biologically the factors responsible for the darkening and lightening effects. It is the work done in this latter period that will is reviewed in this chapter.

Electrical characterization of metal-molecule-silicon junctions

Abstract Direct assembly of molecules onto silicon surfaces is of particular interest for potential employment in hybrid organic-semiconductor devices. In this study, aryl diazonium salts are used to assemble covalently bound molecular groups onto a hydride-passivated, oxide-free n-type Si(111) surface. The reaction of 4-(trimethylsilylethynyl)benzenediazonium tetrafluoroborate generates a molecular layer of 4-(trimethylsilylethynyl)phenylene (TMS-EP) on the Si surface. The monolayer modifies the electrical properties of the interface and exhibits nonlinear current–voltage characteristics, as compared with the ohmic behavior observed from metal- n++-Si(111) junctions. Results of current–voltage measurements at variable temperatures (from 300 to 10 K) on samples made with the TMS-EP molecules do not show significant thermally-activated transport, indicating tunneling is the dominant transport mechanism for this device structure. The measured data is compared to a tunneling model.

Melanocyte-stimulating hormones from sheep pituitary glands.

Abstract The melanocyte-stimulating hormones, α- and β-MSH were isolated from sheep pituitary glands. Ovine α-MSH was found to have the same amino acid sequence as α-MSH from other animals. Three varieties of β-MSH from sheep were studied. One appeared to be identical with bovine β-MSH.

Electrical characterization of metal-molecule-silicon junctions.

Abstract: Direct assembly of molecules onto silicon surfaces is of particular interest for potential employment in hybrid organic‐semiconductor devices. In the study we report here, aryl diazonium salts were used to assemble covalently bound molecular groups on a hydride‐passivated, oxide‐free n‐type Si(111) surface. The reaction of 4‐(trimethylsilylethynyl)benzenediazonium tetrafluoroborate generates a molecular layer of 4‐(trimethylsilylethynyl)phenylene (TMS‐EP) on the n++‐Si(111) surface. The monolayer modifies the electrical properties of the interface and exhibits nonlinear current‐voltage characteristics, as compared with the ohmic behavior observed from metal‐n++‐Si(111) junctions. The result of current‐voltage measurements at variable temperatures (from 300 to 10 K) on samples made with the TMS‐EP molecule does not show significant thermally‐activated transport, indicating that tunneling is the dominant transport mechanism. The measured data is compared to a tunneling model.

THE MECHANISM OF ACTION OF THE MELANOCYTE STIMULATING HORMONES

The melanocyte stimulating hormones, \g=a\-and \g=b\-MSH,are found in the pituitary glands of mammals. These substances are linear polypeptides composed of 13 to 22 amino acids. In very small concentration they can darken the melanocytes of frogs and some other marine animals. The metabolic role of these hormones in man and other mammals is unknown. However, there is good evidence that MSH, when released by the pituitary gland in excessive amounts as in patients with adrenal cortical insufficiency, produces hyperpigmentation of the skin. Thus far only a single \g=a\-MSHbut 3 \g=b\-MSHshave been found. \g=a\-MSHfrom hogs, cattle and sheep is made up of 13 amino acids which are the same as the first 13 amino acids of corticotrophin (ACTH). However, the N terminal serine has an N-acetyl group and the C terminal valine is in the form of an amide. Recently \g=a\-MSHwas found in human and monkey pituitary glands. The structure of \g=a\-MSHfrom human and monkey sources will be described if current investigations are completed before the meetings. Experiments on the isolation and determination of the structure of/3-MSH from human and monkey pituitary glands also will be presented. The synthesis of a-MSH by K. Hofmann and collaborators has made avail¬ able many intermediate peptides ranging from 5 to 13 amino acids as by-pro¬ ducts. Most of the small peptides can darken frog skin. Darkening activity increases as the peptide structure becomes more similar to that of natural a-MSH. The activity of synthetic a-MSH with and without various blocking groups will be discussed. Synthetic and natural a-MSH, porcine ß-MSH and porcine ACTH will be given to a human subject at different times. The skin darkening effects of these four peptides after parenteral administration to human beings will be compared. Department of Medicine, Yale University School of Medicine, New Haven, Conn.