F.H.C. Stewart

Poly-L-alanylglycine

The sequential polymer poly- L -alanylglycine has been synthesized and shown to form a β-structure similar to that found in Bombyx mori silk fibroin. The chain arrangement is such that all the glycyl residues project on one side of the sheet and the alanyl residues on the other. The sheets are packed in pairs with the glycyl surfaces in contact. Structure factor calculations suggest that the inter-sheet distance across the glycyl-glycyl contact is significantly greater than in the model for silk fibroin proposed by Marsh, Corey & Pauling (1955) .

Sequential polypeptides containing L-valyl and γ-methyl-L-glutamyl residues

A series of polypeptides containing ordered sequences of L -valyl (V) and γ-methyl- L -glutamyl (G) residues have been synthesized. The polymers (G x VG) n with x = 0, 1, 2, 3 can all be obtained in a helical conformation in solution. The stability of the helix decreases with decrease in x ; this may be explained in terms of the environment of the V residue on the surface of the α -helix. (G 3 VG) n and the additional polymers (G 3 V 2 G) n and (G 3 ) n gave α -type X-ray diffraction patterns overlaid by β -patterns; the remaining polymers gave β -patterns. α -Helical material could be detected, using infrared spectrometry, in all polymers except (VG) n and (V) n .

Constant and variable regions in glycoprotein hormone beta subunit sequences: Implications for receptor binding specificity

Abstract A quantitative statistical analysis has confirmed the high degree of homology between human luteinizing hormone, follicle stimulating hormone, thyroid stimulating hormone and human chorionic gonadotropin beta subunit sequences, and has demonstrated much higher and extensive homology between follicle stimulating hormone and the others than was previously thought. Three “variable” zones have been detected in these sequences and these are likely to contain many of the residues responsible for the determination of receptor interaction specificity. For luteinizing hormone, comparison of sequences from different species has reduced the range of these residues to positions 1 to 6, 11, 14, 39 to 53, 75, 94, 97, 101, 104 and 108.

Sequential polypeptides containing S-benzyl-l-cysteinyl and γ-ethyl-l-glutamyl residues

A series of polypeptides containing ordered sequences of S-benzyl- L -cysteinyl (C) and γ -ethyl- L -glutamyl (G) residues has been synthesized. Optical rotatory dispersion measurements show that all the polymers adopt some degree of helical conformation in solution. Using polarized infra-red spectrometry α-helical material could be detected in films of all the polymers, as in solution, but always in lower amount than in the parent (G 2 ) n homopolymer † . The polymers (G 3 CG) n , (GCG) n and (GCG 2 ) n gave α -type X-ray diffraction patterns; the remainder gave β -type patterns. In general the stability of the α -helix is lowered by the introduction of C residues. It is suggested that this is due to an unfavourable side chain—main chain interaction.

Pregnancy and Parturition in Marsupials

Publisher Summary The main conclusion to emerge from any review of marsupial reproduction is the pervasive and paramount importance of the corpus luteum to pregnancy, to parturition, and to mammogenesis. While it is young and growing, the corpus luteum inhibits follicular development by some means not involving progesterone and, at the same time, progesterone from the corpus luteum stimulates the endometrial growth and secretion upon which the embryo depends. In macropodids, a transient pulse of progesterone, arising from a briefly altered rate of secretion by the corpus luteum, occurs in the first week of pregnancy and may be necessary to stimulate blastocyst expansion and differentiation. The mature corpus luteum provides progesterone and relaxin which, together or separately, are necessary for the preparation of the pseudovaginal birth canal for parturition. The mature corpus luteum also stimulates lobuloalveolar growth in the mammary gland and the development of prolactinspecific receptors in mammary tissue. In some species, the decline in progesterone from the corpus luteum is closely associated with the onset of parturition, postpartum estrus, and the preovulatory LH surge.