A comparison of structure-activity relationships within alpha-MSH on melanophores of Anolis carolinensis and Rana pipiens

We have compared the structure-function relationship of the tridecapeptide alpha-melanocyte stimulating hormone (alpha-MSH) on the melanophores of the lizard Anolis carolinensis and the frog Rana pipiens by determining the melanosome-dispersing potency of 15 shorter peptide sequences and 8 substituted alpha-MSH analogues. Major differences were found between the lizard and the frog in their response to alpha-MSH peptide fragments and analogues. In Anolis, the sequence Ser-Tyr-Ser- is not as important for the pigmentary response as in Rana since alpha-MSH-(4-13) was nearly as potent (89%) as alpha-MSH-(1-13) (100%), whereas in Rana alpha-MSH-(4-13) potency was reduced to 7.5%. In addition, loss of potency due to removal of residues Pro and Val was more marked in Rana (alpha-MSH-(1-11) = 0.1%) than in Anolis (alpha-MSH-(1-11) = 1%), suggesting that this C-terminal sequence is necessary for pigmentary activity in the frog melanophore. These results together with those of other peptide fragments and analogues have led us to define the minimal pigmentary sequence of alpha-MSH as alpha-MSH-(4-12) in Anolis in contrast to alpha-MSH-(1-13) in Rana. This suggests that Anolis and Rana alpha-MSH receptors recognise different message amino acids of the alpha-MSH peptide sequence even though the final response (melanosome dispersion) is the same.     

A rapid extraction method for detecting aflatoxin producing isolates

A rapid extraction method for screening aflatoxin producing potential ofAspergillus flavus group isolates is described. The method is performed using a moist wheat medium with ca. five infected grains extracted with 2 mL of chloroform, and using thin layer chromatography. This method was proved with 95A. flavus isolates from animal feeds.     

Fluxes of h and k in corn roots : characterization and stoichiometries using ion-selective microelectrodes

We report here on an experimental system that utilizes ion-selective microelectrodes to measure the electrochemical potential gradients for H⁺ and K⁺ ions within the unstirred layer near the root surface of both intact 4-day-old corn seedlings and corn root segments. Analysis of the steady state H⁺ and K⁺ electrochemical potential gradients provided a simultaneous measure of the fluxes crossing a localized region of the root surface. Net K⁺ influx values obtained by this method were compared with unidirectional K⁺ (⁸⁶Rb⁺) influx kinetic data; at any particular K⁺ concentration, similar values were obtained by either technique. The ionspecific microelectrode system was then used to investigate the association between net H⁺ efflux and net K⁺ influx. Although the computed H⁺:K⁺ stoichiometry is dependent upon the choice of diffusion coefficients, the values obtained were extremely variable, and net K⁺ influx rarely appeared to be charge-balanced by H⁺ efflux. In contrast to earlier studies, we found the cortical membrane potential to be highly K⁺ sensitive within the micromolar K⁺ concentration range. Simultaneous measurements of membrane potential and K⁺ influx, as a function of K⁺ concentration, revealed similar K_m values for the depolarization of the potential (K_m 6-9 micromolar K⁺) and net K⁺ influx (K_m 4-7 micromolar K⁺). These data suggest that K⁺ may enter corn roots via a K⁺-H⁺ cotransport system rather than a K⁺/H⁺ antiporter.     

Glucose stimulates the biosynthesis of rat I and II insulin to an equal extent in isolated pancreatic islets

The effects of glucose on insulin biosynthesis were studied by measuring the incorporation of radiolabelled amino acids into proinsulin/insulin in isolated rat islets. The islets were pulse labelled for 15 min with [3H]leucine (present in rat insulin I and II) or [35S]methionine (unique to rat insulin II) and then incubated for a 165 min post-label (chase) period during which the majority of labelled proinsulin was converted to insulin but under conditions whereby greater than 95% of radiolabelled proinsulin or insulin was retained in the islets. The newly synthesized, labelled, insulin was analyzed by high performance liquid chromatography. Rat I and II insulin biosynthesis was stimulated by 16.7 mM glucose to the same extent.     

Effects of chronic allopurinol therapy on purine metabolism in Duchenne muscular dystrophy

Adenine, adenosine, inosine, hypoxanthine, xanthosine, xanthine, guanine and guanosine blood levels in 11 Duchenne muscular dystrophy patients treated with allopurinol, 10 untreated patients and 8 healthy controls, were determined by HPLC. Serum ADA, PNP and 5'-NT were also determined. Untreated patients showed lower adenine (p less than 0.001) and higher adenosine, xanthine, ADA and PNP levels (p less than 0.01) than controls. Treated patients had lower adenine and higher xanthine levels (p less than 0.001), but higher hypoxanthine, xanthosine and guanine levels (p less than 0.001), than controls, with normal ADA and PNP. The changes observed in ADA and PNP levels suggest an involvement of these enzymes in accelerated degradation of purines in Duchenne dystrophy.