LK-66 M

The Michaelis-Menten equation is usually expressed in terms ofkcatandKmvalues:v=kcat[S]/(Km+ [S]). However, it is impossible to interpretKmin the absence of additional information, while the ratio ofkcat/Kmprovides a measure of enzyme specificity and is proportional to enzyme efficiency and proficiency. Moreover,kcat/Kmprovides a lower limit on the second order rate constant for substrate binding. For these reasons it is better to redefine the Michaelis-Menten equation in terms ofkcatandkcat/Kmvalues:v=kSP[S]/(1 +kSP[S]/kcat), where the specificity constant,kSP=kcat/Km. In this short review, the rationale for this assertion is explained and it is shown that more accurate measurements ofkcat/Kmcan be derived directly using the modified form of the Michaelis-Menten equation rather than calculated from the ratio ofkcatandKmvalues measured separately. Even greater accuracy is achieved with fitting the raw data directly by numerical integration of the rate equations rather than using analytically derived equations. The importance of fitting to derivekcatandkcat/Kmis illustrated by considering the role of conformational changes in enzyme specificity wherekcatandkcat/Kmcan reflect different steps in the pathway. This highlights the pitfalls in attempting to interpretKm, which is best understood as the ratio ofkcatdivided bykcat/Km.

A new rectangular-shaped carbadecaphyrin was successfully synthesized by introducing a terphenylene unit ( m- m- m) in the macrocyclic core. The terphenylene moiety offers an open framework with multiple binding pockets to stabilize two Rh(I) ions in the core. The photophysical and structural studies reveal the non-aromatic character of the ligand and its bis-Rh(I) complex.

Members ofVenturiales(Dothideomycetes) are widely distributed, and comprise saprobes, as well as plant, human and animal pathogens. In spite of their economic importance, the general lack of cultures and DNA data has resulted in taxa being poorly resolved. In the present study five loci, ITS, LSU rDNA,tef1,tub2andrpb2are used for analysing 115 venturialean taxa representing 30 genera in three families in the current classification ofVenturiales. Based on the multigene phylogenetic analysis, morphological and ecological characteristics, one new family,Cylindrosympodiaceae, and eight new genera are described, namelyBellamyces,Fagicola, Fraxinicola,Fuscohilum,Neofusicladium,Parafusicladium,PinaceicolaandSterila. In addition, 12 species are described as new to science, and 41 new combinations are proposed. The taxonomic status of 153 species have been re-evaluated with 20 species excluded fromVenturiales. Based on this revision ofVenturiales, morphological characteristics such as conidial arrangement (solitary or in chains) or conidiogenesis (blastic-solitary, sympodial or annellidic), proved to be significant at generic level.Venturiaas currently defined represents a generic complex. Furthermore, plant pathogens appear more terminal in phylogenetic analyses withinVenturiaceaeandSympoventuriaceae, suggesting that the ancestral state ofVenturialesis most likely saprobic.