Frog skin

Another class of 5-selective peptides, isolated from extracts of frog skin, is the deltorphins. These compounds are based on the stmcture... 

The magaiitins are a class of hnear, cationic, faciaUy amphipathic and hehcal antibacterial peptides derived from frog skin [51]. The magaiitins exhibit highly selective and potent antimicrobial activity against a broad spectrum of organisms [52, 53]. As these peptides are faciaUy amphipathic, the magainins have a cationic heli-... 

Laticauda semifasciata venom added to the outside bathing solution of frog skin causes an increase in transmural potential difference and short-circuit current, indicating the change in the Na transport system. The venom-induced stimulatory effects can be explained as being either due to an increase in Na permeability of the outer membrane or by an increase in the activity of the Na -pump (22). 

A classical example of active transport is the transport of sodium ions in frog skin from the epithelium to the corium, i.e. into the body. The principal ionic component in the organism of a frog, sodium ions, is not washed out of its body during its life in water. That this phenomenon is a result of the active transport of sodium ions is demonstrated by an experiment in which the skin of the common green frog is fixed as a... 

The rate of the active transport of sodium ion across frog skin depends both on the electrochemical potential difference between the two sides of this complex membrane (or, more exactly, membrane system) and also on the affinity of the chemical reaction occurring in the membrane. This combination of material flux, a vector, and chemical flux (see Eq. 2.3.26), which is scalar in nature, is possible according to the Curie principle only when the medium in which the chemical reaction occurs is not homogeneous but anisotropic (i.e. has an oriented structure in the direction perpendicular to the surface of the membrane or, as is sometimes stated, has a vectorial character). 

J DeLong, MM Civan. (1983). Microelectrode study of K+ accumulation by tight epithelia. I. Baseline values of split frog skin and toad urinary bladder. J Membr Biol 72 183-193. 

W Van Driessche, D Erlij. (1983). Noise analysis of inward and outward Na+ currents across the apical border of ouabain-treated frog skin. Pfluegers Arch 398 179-188. 

Ussing, H. H., Anomalous transport of electrolytes and sucrose through the isolated frog skin induced by hypertonicity of the outside bathing solution, Ann. N. Y. Acad. Sci. 1966, 137, 543-555. 

Blankemeyer, J.T. and C.R. Hefler. 1990. Effect of naphthalene on sodium active transport in the frog skin. Bull. Environ. Contam. Toxicol. 45 627-632. 

Ussing, H. H. and Zerahn, K. (1951). Active transport of sodium as the source of electric current in the short-circuited isolated frog skin, Acta Physiol. Scand., 23, 110-127. 

Kirschner, L. B. (1983). Sodium chloride absorption across the body surface frog skins and other epithelia, Am. J. Physiol., 244, R429-R443. 

Since then, the dietary hypothesis for the origin of several classes of lipophilic alkaloids in frog skins has been strengthened several times. Thus,... 

Ussing HH (1949) Active ion transport through the isolated frog skin in the light of tracer studies. Acta Physiol Scand 17 1-37... 

McClean S, Robinson RC, Shaw C, Smyth WR 2002. Characterization and determination of indole alkaloids in frog-skin secretions by electrospray ionization trap mass spectrometry. Rapid Commun Mass Spectrom 16 346. 

FSIP frog skin insulinotropic peptide from frog Agalychnis litodryas G (Gly) glycine or glycyl... 

Metabolism of tryptophan leads to an important neurotransmitter, serotonin. Adding a couple of methyl groups to the amino function of serotonin creates bufotenine, a psychoactive compound found in frog skin and some beans. In point of fact, there are a number of derivatives of tryptamine that are psychoactive. 

Zielinski, W. J. and Barthalmus, G. T. (1989). African clawed frog skin compounds antipredatoiy effects on African and North American watersnakes. Animal Behaviour 38,1038-1086. 

The frogs are killed with ether and carefully skinned using forceps and scissors. The skin is then cut into small pieces and soaked in methanol at a proportion of 500 ml per 250 frog skins. 

Compound Frog Skin Assay Lizard Skin Assay... 

All potencies are relative to a-MSH In dose-response assays. Relative potency cone, of a-MSH at 50Z responae/conc. of peptide at 50Z response. The cyclic peptides 11 and 12 have much higher minimal effective dose potencies ( 10,000) In the frog skin system. 

The 4-10 cyclic analog 14 (Table I) Is quite Inactive In both systems, but relative to the linear pseudo-lsosterlc analog 15 much more so In the lizard skin system (29). Addition of Lys-11 to the cyclic 4-10 analog to give analog 13 leads to a large Increase In potency In the lizard but not the frog skin system (30). 

Examination of the data In Table I and other data not reported here provides evidence that conformation restriction (In this case cycllzatlon) favors specificity at one physiological receptor type over another. For example, In the cyclic 4-13 analog (12, Table I) about a 60-fold relative specificity preference for the frog skin system Is seen, but It Is actually more than that due to the 5- to 10-fold greater absolute potency of a-MSH In the frog skin system. 

Figure 1. Schematic representation of a proposed reverse turn conformation of a-MSH at the frog skin receptor. Reproduced with permission from Ref. 50. Copyright 1982, Zoological Society.

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