Phospholipid exchange activity in developing rat brain

Phospholipid exchange activity has been determined in the supernatant fraction of rat brain from birth through to maturity by measuring the protein-catalysed transfer of total and individual 32P-labelled phospholipids from microsomal membranes to mitochondria, and the transfer of [14C]phosphatidylcholine from liposomes to mitochondria. Transfer activity has also been compared in brain and liver supernatant. Overall phospholipid exchange activity in the brain increased only slightly with age. The activity at birth was 75% of the adult value. However, the transfer of individual phospholipids showed markedly different trends during postnatal brain development. The transfer of phosphatidylinositol (PI) and ethanolamine phospholipids increased postnatally to a maximum at 9 days of age, with lowest values in adult brain. Phosphatidylcholine (PC) transfer increased from 9 days to reach maximum values in the mature brain. The transfer of sphingomyelin was highest immediately after birth. PI transfer activity was higher in brain than liver, while PC and ethanolamine phospholipid transfer activity was higher in liver. The heterogeneity of phospholipid exchange proteins in central nervous system tissue is reflected in the developmental changes in exchange activity towards individual phospholipids. The various exchange proteins appear to have separate induction mechanisms. The presence of exchange-protein activity from birth in the rat indicates the functional importance of phospholipid transport during cell acquisition and membrane proliferation. Activity is not primarily associated with membrane formation such as the formation of the myelin sheath, and therefore is more likely to be involved in the process of phospholipid turnover.     

The use of resonance Raman spectroscopy to monitor catalytically important bonds during enzymic catalysis. Application to the hydrolysis of methyl thionohippurate by papain.

Resonance Raman spectra were obtained of the dithioacyl-enzyme intermediate produced during the papain-catalayzed hydrolysis of methyl thionohippurate. Intense resonance Raman features were observed in (formula; see text) and (formula; see text) stretching regions from the intermediate's (formula; see text) chromophore. These results demonstrate that by using a single atom replacement, i.e. sulfur for oxygen, the catalytically crucial bonds in the ester moiety can be monitored during enzymolysis via the resonance Raman spectrum. The method can be extended to other enzymes whose catalytic mechanisms involve the formation of a thiol-acyl intermediate.     

Demographic analysis of mite populations: extensions of stable theory

Mites have simple life styles and overlapping generations, thus analysis of their populations using stable theory (Lotka's equation) is particularly appropriate. While use of this demographic framework is widespread among mite researchers, the specific context in which it is applied is typically restricted to the conventional life table and associated parameters.In this paper we extend the use of the basic principles of stable population theory in mite populations to include: (i) expectation of future life expectancy and reproduction; (ii) effect of developmental time on population growth rate; (iii) sensitivity analysis of a two-sex model; (iv) distribution of biomass and productivity in stable mite populations; (v) demographic theory of kinship as applied to mites; and (vi) mite mass-rearing. Implications of each are briefly discussed in the context of mite ecology and management.