A populational survey of amino acids in Prosopis species from North and South America

Leaf extracts of 540 plants representing 24 species of the genus Prosopis from North and South America were analyzed by 2-D PC and high voltage electrophoresis for their protein and non-protein amino acids. In addition to the presence of the usual protein amino acids, most of the species examined contained high concentrations of the non-protein amino acids, pipecolic acid, 4-hydroxypipecolic acid and proline.     

Replication slippage may cause parallel evolution in the secondary structures of mitochondrial transfer RNAs

Presence of the dihydrouridine (D) stem in the mitochondrial cysteine tRNA is unusually variable among lepidosaurian reptiles. Phylogenetic and comparative analyses of cysteine tRNA gene sequences identify eight parallel losses of the D-stem, resulting in D-arm replacement loops. Sampling within the monophyletic Acrodonta provides no evidence for reversal. Slipped-strand mispairing of noncontiguous repeated sequences during replication or direct replication slippage can explain repeats observed within cysteine tRNAs that contain a D-arm replacement loop. These two mechanisms involving replication slippage can account for the loss of the cysteine tRNA D-stem in several lepidosaurian lineages, and may represent general mechanisms by which the secondary structures of mitochondrial tRNAs are altered.      

A heliangolide from Chromolaena glaberrima

The investigation of Chromolaena glaberrima afforded, besides the known heliangolide chromolaenide, a new 4-dehydrochromolaenide. The structure of the new compound was elucidated by spectroscopic methods.     

Sesquiterpene lactone and diterpene constituents of helianthus annuus

One new furanoheliangolide derivative, 4,5-dihydroniveusin A, as well as the known compounds niveusin B and argophyllin A and B, were isolated from a Texas population of Helianthus annuus. Three previously characterized diterpene acids, grandifloric acid, ciliaric acid and 17-hydroxy-ent-isokaur-15(16)-en-19-oic acid were the principal constituents of this population.     

ON THE MECHANISM OF THE INHIBITION OF GROWTH BY XYLULOSE IN CHLOROCOCCUM ECHINOZYGOTUM1,2

We previously established that xylulose inhibits the growth of the green alga Chlorococcum echinozygotum. Utilizing experiments involving exposure of the alga to NaHC¹⁴O₃, it was possible to show by counting the C¹⁴ activity of methanolic extracts of the algal cells that xylulose inhibited CO₂ uptake. Subsequently it was shown that xylulose does not inhibit or otherwise influence the Hill reaction in this alga. Several enzymes related to xylulose metabolism were investigated. It was found that xylulokinase was active in C. echinozygotum while phosphoketolase activity was absent. Transketolase was present but its activity was not notably affected by xylulose. Crude carboxydismutase preparations were found to be inhibited by xylulose and xylulose 5-phosphate. However, as carboxydismutase was purified further, this inhibition was relatively less. When xylulose 1,5-diphosphate was prepared synthetically, this compound was found to be the most effective inhibitor of purified algal carboxydismutase. We conclude that d -xylulose enters the cells of C. echinozygotum where it is converted to d -xylulose 1,5-diphosphate which acts as a competitive inhibitor of carboxydismutase.