Carboxyfluorescein fluorescence experiments.

Although fluorescence is a powerful and much used tool in Biology there are very few applications for teaching this topic in Biochemistry courses. Some classical experiments in carboxyfluorescein fluorescence are presented here, including recording a fluorescence spectrum, quenching by oxygen, effect of concentration and pH on fluorescence signal, and a Stern-Volmer representation for a dynamic quenching.

Newly found 2-N-acetyl-2,6-dideoxy-beta-glucopyranose containing methyl glucose polysaccharides in M.bovis BCG: revised structure of the mycobacterial methyl glucose lipopolysaccharides.

The specific mycobacterial methyl polysaccharides 3- O -methyl mannose polysaccharide (MMP) and the 6- O -methyl glucose lipopolysaccharides (MGLPs) were shown to modulate the fatty acid biosynthesis by the mycobacterial fatty acid synthetase I (FAS I). This activity is attributed to their fatty acid complexing properties allowing the release of the neo synthesized fatty acyl chain from the enzyme and probably their transport in the cell. To elucidate, at a molecular level, the mechanism of this unusual kind of polysaccharide-lipid biological interaction, we first analyzed, by mass spectrometry and proton nuclear magnetic resonance (1H NMR) spectroscopy, the structure of the polysaccharidic backbone (MGPs) of the MGLPs from Mycobacterium bovis BCG. This work reveals that this strain produces a new kind of MGP containing an unusual monosaccharide never described in the mycobacterial genus: a 2- N -acetyl-2,6-dideoxy-beta-glucopyranosyl. In addition,1H NMR data afforded evidence for the revision of three glycosidic linkages described previously. These modifications affect mainly the reducing end tetrasaccharide and have great consequences on the previously proposed molecular model of the MGP.

Involvement of FtsZ in coupling of nucleoid separation with septation.

The cell-cycle parameters of an Escherichia coli strain expressing essential division gene ftsZ at one-fifth of its normal level, because of antisense regulation by DicF RNA, have been analysed. Inhibition of FtsZ expression affects neither the generation time nor the replication initiation mass, the C period, or the constriction period, but it does dramatically retard the initiation of constriction relative to replication termination. Separation of the nucleoids is equally postponed, indicating that division is not coupled to termination of replication, but to partitioning. The severe inhibition of nucleoid separation by DicF RNA, and its suppression by overproduction of FtsZ, suggest a role for FtsZ in the control of separation, and consequently in the coupling of separation and division. We suggest that the normal pattern of nucleoid separation previously found in cells deficient in ftsZ function was a consequence of the loss of a negative effect exerted by FtsZ on separation. In agreement with this view, we find that nucleoid separation is temporarily inhibited after arrest of FtsZ synthesis, but is later resumed as FtsZ is further diluted into the elongating filaments.