Leucine transport in membrane vesicles from Chironomus riparius larvae displays a mélange of crown-group features.

Leucine uptake into membrane vesicles from larvae of the midge Chironomus riparius was studied. The membrane preparation was highly enriched in typical brush border membrane enzymes and depleted of other membrane contaminants. In the absence of cations, there was a stereospecific uptake of l-leucine, which exhibited saturation kinetics. Parameters were determined both at neutral (Km 33 +/- 5 microM and Vmax 22.6 +/- 6.8 pmol/7s/mg protein) and alkaline (Km 46 +/- 5 microM and Vmax 15.5 +/- 2.5 pmol/7s/mg protein) pH values. At alkaline pH, external sodium increased the affinity for leucine (Km 17 +/- 1 microM) and the maximal uptake rate (Vmax 74.0 +/- 12.5 pmol/7s/mg protein). Stimulation of leucine uptake by external alkaline pH agreed with lumen pH measurements in vivo. Competition experiments indicated that at alkaline pH, the transport system readily accepts most L-amino acids, including branched, unbranched, and alpha-methylated amino acids, histidine and lysine, but has a low affinity for phenylalanine, beta-amino acids, and N-methylated amino acids. At neutral pH, the transport has a decreased affinity for lysine, glycine, and alpha-methylleucine. Taken together, these data are consistent with the presence in midges of two distinct leucine transport systems, which combine characters of the lepidopteran amino acid transport system and of the sodium-dependent system from lower neopterans.

Liver cirrhosis associated with chronic hepatitis B virus infection in childhood.

We evaluated the prevalence and the clinical features of liver cirrhosis associated with chronic hepatitis B virus (HBV) infection in a prospective study of 292 consecutive children who were chronic HBsAg carriers with increased aminotransferase activity. Liver histologic changes at presentation were consistent with cirrhosis in 10 (3.4%) patients (100% boys, mean age 4.0 +/- 3.3 years). In none of the remaining children, including 166 with histologic evidence of chronic active hepatitis, did the condition progress to cirrhosis during an observation period of 1 to 10 years. This lack of progression suggests that cirrhosis is an early complication of chronic HBV disease in some patients. A higher prevalence of delta infection and increased incidence of blood transfusions were observed in patients with cirrhosis, supporting the hypothesis that superinfection with delta or non-A, non-B agents may play a synergistic role. Eight of 10 patients had histologic features of disease activity at presentation, although only two had symptoms. During follow-up, persistence of disease activity was observed only in the three delta antigen-positive patients. None of the patients with inactive cirrhosis have developed signs of liver failure or portal hypertension.