No abstract

Experimental hyperphenylalaninemia has been induced in 5-day-old chicks by dietary treatments with phenylalanine and alpha-methylphenylalanine. An increase of nearly 8-fold in plasma Phe/Tyr ratio was found after 4 days of supplementation the standard diet with 5% phenylalanine plus 0.4% alpha-methylphenylalanine. The increase in this ratio was about 13-fold after 9 days of the same treatment. Similar results were observed in brain and liver, although the increases were smaller than those found in plasma. Total body, brain and liver weight decreased after 9 days of treatment. Phenylalanine plus alpha-methylphenylalanine administration to 5-day-old chicks produced a significant decrease in the 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate-5-pyrophosphate decarboxylase specific activities from both brain and liver. These results demonstrated for the first time that experimental hyperphenylalaninemia inhibited different enzyme activities directly implicated in the regulation of cholesterogenesis. Therefore, a reduced cholesterol synthesis in brain may evidenciate the theory of an impaired myelination leading to mental retardation in phenylketonuria patients.

Phenylalanine, phenylpyruvate and phenylacetate produced a considerable inhibition of chick liver mevalonate 5-pyrophosphate decarboxylase while mevalonate kinase and mevalonate 5-phosphate kinase were not significantly affected. Phenolic derivatives of phenylalanine produced a similar inhibition of decarboxylase activity than that found in the presence of phenyl metabolites. The degree of inhibition was progressive with increasing concentrations of inhibitors (1.25-5.00 mM). Simultaneous supplementation of different metabolites in conditions similar to those in experimental phenylketonuria (0.25 mM each) produced a clear inhibition of liver decarboxylase and 3-hydroxy-3-methylglutaryl-CoA reductase. To our knowledge, this is the first report on the in vitro inhibition of both liver regulatory enzymes of cholesterogenesis in phenylketonuria-like conditions. Our results show a lower inhibition of decarboxylase than that of reductase but suggest an important regulatory role of decarboxylase in cholesterol synthesis.

SUMMARYInfluence of season on the terpene composition of Pinus halepensis and Pinus sylvestris was investigated. The essential oil of twigs and needles from a preselected plot of pines was investigated from October to June. In P. halepensis, the average composition during this time was 27·2% α-pinene, 65·0% sabinene, 7·2% 3-carene and 0·5% β-pinene in the essential oil of twigs; 32·1% α-pinene, 35·9% sabinene, 18·5% terpinolene, 4·3% 3-carene, 3·1% β-pinene and 6·1% thujene, limonene, β;-phellandrene and γ-terpinene in the essential oil of needles. In P. sylvestris, the average composition was 49·2% α-pinene, 30·1% sabinene, 14·9% β-pinene and 7·9% limonene in the essential oil of twigs; 69·5% α-pinene, 14·9% camphene, 9·1% β-pinene, 3·6% sabinene and 2·8% limonene in the essential oil of needles. The maximum amount of sabinene coincides with the minimum of α-pinene, both in twigs and needles essential oil from P. halepensis and P. sylvestris. The month-to-month changes in the oil composition are statistically significant for the most part. It is of interest to point out the decrease of sabinene content of needles essential oil in comparison with the twigs essential oil, with the simultaneous increaseof terpinolene in P. halepensis and camphene in P. sylvestris.

Very small sample sizes frequently become the limiting factor in biochemical and biomembrane studies in which routine quantification of protein and bulk lipids are required. The procedure described here allows the simultaneous determination of protein and lipid without initial, multiple aliquots. The method is based on the quantitative precipitation of proteins from a defined hexane/isopropanol mixture. The liquid phase resulting after decanting and concentrating to dryness can then be used to assay the lipid content directly. Quantitative assay of protein can be achieved after resuspension of the pelleted material by addition of sodium dodecyl sulfate (0.1%) and deoxycholate (1%). The method is also applicable to other types of lipid- and protein-containing samples with a broad range of protein/lipid ratios and lipid compositions, as they occur, for example, in serum lipoproteins.