Substrate stabilization: genetically controlled reciprocal relationship of two human enzymes

5-Phosphoribosyl-l-pyrophosphate, a substrate shared by adenine phosphoribosyltransferase and hypoxanthine-guanine phosphoribosyltransferase, accumulates in human erythrocytes lacking hypoxanthine-guanine phosphoribosyltransferase. 5-Phosphoribosyl-l-pyrophosphate added to purified adenine phosphoribosyltransferase stabilizes it against heat inactivation. The increased activity of adenine phosphoribosyltransferase seen in erythrocytes deficient in hypoxanthine-guanine phosphoribosyltransferase may result from substrate stabilization of this enzyme in vivo.     

Behavior and phylogeny: constriction in ancient and modern snakes

Comparative analyses of behavior have an underappreciated potential for revealing the role of ethoecological factors in the origins of higher taxa. Twenty-seven species (13 genera) in the advanced family Colubridae exhibited 19 patterns of coil application; one or two patterns were usually consistent within a genus. Forty-eight species (26 genera) in the primitive families Acrochordidae, Aniliidae, Boidae, and Xenopeltidae usually used a single pattern, despite differences in age, size, shape, habitat, and diet. This implies the shared retention of an action pattern used by their common ancestor no later than the early Paleocene. Constriction must have been used as a prey-killing tactic very early in the history of snakes and might have been a behavioral "key innovation" in the evolution of their unusual jaw mechanism.     

Active T-cell receptor genes have intron deoxyribonuclease hypersensitive sites

The T-cell receptor beta-chain gene has a nuclease hypersensitive site in several kinds of T cells, which does not appear in B cells expressing immunoglobulins. Conversely, the kappa immunoglobulin gene shows a known hypersensitive site at its enhancer element in B cells, as expected, but this site is absent in T cells. As is the case with immunoglobulin genes, the T-cell receptor site lies within the gene, in the intron separating joining and constant region segments. These nuclease hypersensitive DNA configurations in the introns of active T-cell receptor and immunoglobulin genes may arise from control elements that share ancestry but have diverged to the extent that each normally acts only in lymphoid cells which use the proximal gene product.     

Microbodies in germinating fern spores: evidence for glyoxysomal activity

Enzymes of the glyoxylate cycle, isocitrate lyase and malate synthase, are active during the germination of spores of the fern Dryopteris filix-mas. Increases in activity of both enzymes are correlated with the breakdown of lipid reserves. The occurrence of these enzymes suggests that the microbodies previously described in these spores are glyoxysomes.