Enzyme formation in higher plant tissue

Summary Ageing slices of artichoke tuber or carrot root produced a substance, characterised as a protein, which when added to freshly cut slices inhibited invertase development. For maximum effect, it was necessary to expose the tissue to inhibitor immediately on excision, and this resulted in a slower rate of enzyme production and a lower final level. We suggest that there is an interaction between gibberellin, whose production is initiated by wounding, and the inhibitor. Bacterial infection was not the cause of the results obtained.     

Renal vasculature and excretory system of the agamid lizard,Ctenophorus ornatus

The structure and ultrastructure of the vasculature and nephric tubules of the kidney of the Ornate Dragon Lizard, Ctenophorus (=Amphibolurus) ornatus, was investigated by light microscopy and scanning electron microscopy of resin casts. Compared with other agamid lizards, the arterial supply of only two arteries per kidney is small. The number of glomeruli per kidney in C. ornatus, at between 400 and 600, is low by reptilian standards and very low for lizards. The glomeruli are not only comparatively few in number but are also simple in the nature of their capillary configuration. These features are suggestive of a greatly reduced surface area for arterial filtration. In contrast to the small arterial supply, the afferent venous supply, the renal portal system (RPS), is substantial and forms an extensive capillary network throughout the kidneys. No venous shunts were found in the kidneys, suggesting that the venous network is functioning as a true portal system. Valves were not identified within the RPS, implying that neural control of general vascular tone could alter velocity and perhaps the direction of blood flow by changing pressure profiles. The nephroi are comparatively short and display features consistent with the production of urate precipitates as the primary nitrogenous waste product. A close association between the distal tubule (DT) and the glomerular hilus may demonstrate a simple form of a juxtaglomerular apparatus. The finding of aglomerular tubules indicates an important role for tubular secretion. The results of this study indicate that these lizards may have a reduced reliance on filtration for homoiostasis and a greater reliance on tubular secretion. © 1993 Wiley-Liss, Inc.     

Pharmacologic study of inflammatory processes. Modification of polynuclear neutrophil chemotaxis]

A study of rat polymorphonuclear chemotaxis has been made by a direct microscopic method and the effect of inflammatory reactions induced by carrageenan, calcium pyrophosphate and complete Freund's adjuvant has been studied. In addition the action of various drugs such as cholera toxin, colchicine, prostaglandins and certain immunomodulators, was investigated. The results have been analysed with special regard to the role of chemotaxis in inflammatory responses.     

Rat liver polysome N alpha-acetyltransferase: substrate specificity.

The substrate specificity of polysome rat liver N alpha-acetyltransferase (NAT) has been examined by utilizing a series of synthetic and natural substrates that has been systematically altered with respect to N-terminal sequence and length. Families of peptides of the structure S-Y-S-G-G-L-L-L were generated by successively replacing the N-terminal serine, the penultimate tyrosine, and the antepenultimate serine with all 19 commonly occurring amino acids, which were then assessed for their reactivity with the rat liver enzyme. Only peptides with N-terminal serine, alanine, methionine, leucine, and phenylalanine were modified. Glycine, lysine, arginine, valine, isoleucine, and tryptophan in the second position are (with N-terminal serine) strongly inhibitory, and proline completely blocks modification. Third-position substitutions have less of an effect on NAT activity with glycine, aspartic acid, glutamic acid, and tryptophan being most inhibiting (with N-terminal Ser-Tyr). These observations are generally in agreement with in situ modifications although there are some significant differences particularly with respect to the amino-terminal residues. Optimal chain length was determined to be 10-11 residues with either synthetic peptides of the structure S-Y-S-(G)n-L-L-L or adrenocorticotropin (ACTH) sequences ranging from 8 to 39 residues. The ACTH peptides were generally found to be severalfold better substrates than the corresponding synthetic ones. Activity was not affected by increased chain length beyond approximately 17 residues. These data support the view that polysome-catalyzed N alpha-acetylation occurs as a cotranslational event on nascent chains of about 20-40 amino acids in length.