Phenylalanine hydroxylase levels in diabetic rats

Howard, Katrina; Donlon, John

doi:10.1042/bst0130465

Cited by 7 publications

(7 citation statements)

References 3 publications

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“…Longer-term control appears to involve modulation of enzyme concentration. Experimentally induced diabetes promotes alterations in hydroxylase activity which are the result o f changes in enzyme concentration (Donlon & Beirne, 1982;Howard & Donlon, 1985). We show here that diabetes-related changes in phenylalanine hydroxylase expression are associated with alterations in the functional activity of hydroxylase-specific mRNA.…”

supporting

confidence: 52%

“…The change in activity reflects an increase in the abundance of hydroxylase protein as shown by immunoblot analyses. These observations are consistent with immunotitration data obtained by ourselves and other workers (Santana ei al., 1985;Howard & Donlon, 1985). Analysis of the functional activity of hepatic poly(A)RNA, from diabetic animals, in a translation system in vitro indicated that there was an increased capacity to direct the synthesis of the hydroxylase relative to total protein synthesis.…”

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confidence: 99%

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Impact of experimental diabetes on phenylalanine hydroxylase expression in rat liver

Taylor

Green

Fisher

1988

Biochemical Society Transactions

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627th MEETING, NOTTINGHAM 1057 activation is lower than that found in lysosomes (Ohkuma & Poole, 1978) our results suggest that the activation in vivo may depend on components or structures that induce conformational changes at less acidic pH values. This may involve membrane interactions since hydrophilic/hydrophobic interactions appear to be important. Internal cleavages in the precursor must occur after transport to the lysosome since no change in M , was observed after reduction with dithiothreitol. The K , and k,,, values obtained for the degradation of Z-Phe-Arg-7-(4-methyI)coumarylamide (NHMec) of the activated precursors suggest that cathepsin L may be potentially more active in vivo than in vitro. The glycosyl residues did not alter the conditions required for activation and only slightly altered the kinetic parameters.

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confidence: 52%

mentioning

confidence: 99%

Impact of experimental diabetes on phenylalanine hydroxylase expression in rat liver

Taylor

Green

Fisher

1988

Biochemical Society Transactions

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“…The effects of starvation are rather similar to those of experimentally induced diabetes, where regulation occurs both pre-and post-translationally (Donlon & Beirne, 1982;Howard & Donlon, 1985;Howard & Donlon, 1988). Starvation may provide a model to develop some clues as to the mechanism(s) involved in the regulation of the expression of phenylalanine hydroxylase.…”

mentioning

confidence: 76%

Effects of starvation on rat phenylalanine hydroxylase activities

Walsh

Donlon

1989

Biochemical Society Transactions

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378BIOCHEMICAL SOCIETY TRANSACTIONS centrations of 0.43-1.22 pglml. N o significant correlation was found.The results for isoenzyme V are shown in Figs. l ( a ) and l(6). At pH 8.05, V,,,, values fell between 3.54 and 4.19 pmol/min per mg at protein concentrations of 0.6 1-1.84 pg/ml of assay volume. A significant correlation was noted between V,,, values and protein concentration ( Fig. la). At pH 8.60, V,,, values were 3.76-7.04 pmol/min per mg at protein concentrations of 0.90-2.3 pg/ml of assay volume. A significant correlation was not found (Fig. 16).The mean values (and S.D.S) of Vmm, found were: isoenzyme 111, pH 8.05, 4.76 (k0.28); pH 8.60, 5.32, (k0.73); isoenzyme IV, pH 8.05, 2.07 (k0.49); pH 8.60, 5.84 ( f 0.40) and isoenzyme V, pH 8.05, 3.84 ( k 0.18); pH 8.60, 5.38( k 1.01).The following conclusions can be drawn: (i) V,,,, values are lower at pH 8.05 than at pH 8.60 for all (ii) The S.D.S are smaller at pH 8.05 with the exception of (iii) V,,,, values for isoenzyme IV at pH 8.05 are lower (iv) V,,,, values are very similar at pH 8.60. (v) The values of V,,,, given are in reasonable agreement with the maximum specific activities observed for column three forms investigated. isoenzyme IV.than the values for isoenzymes 111 and V.fractions of peak activity after DEAE-cellulose chromatography (Nicholas & Bachelard, 1969). (vi) The results appear to contradict the earlier findings that enzyme activity was not dependent on pH in glycine/ NaOH buffer (Nicholas, 1989a) at saturating concentrations of substrate.(vii) The significant decrease in V,,, with decrease in protein concentration is unusual in the absence of effector molecules, but might indicate some dissociation into inactive monomers, cf. muscle aldolase (Bernfeld et al., 1965).

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“…Experimentally induced diabetes in rats is associated with a significant increase in metabolic flux through the phenylalanine-catabolic pathway in isolated liver cells (Carr & Pogson, 1981). An increase in immunoreactive hydroxylase activity in liver cell extracts is also observed (Donlon & Beirne, 1982;Howard & Donlon, 1985;Santana et al, 1985). Changes in the control of phenylalanine hydroxylase phosphorylation state may also accompany the onset of diabetes (Donlon & Beirne, 1982;Stanley et al, 1985).…”

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confidence: 96%

The role of insulin in the modulation of glucagon-dependent control of phenylalanine hydroxylation in isolated liver cells

Fisher¹,

Dickson²,

Pogson³

1987

Biochemical Journal

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The stimulation of phenylalanine hydroxylation in isolated liver cells by sub-maximally effective concentrations of glucagon (less than 0.1 microM) is antagonized by insulin (0.1 nM-0.1 microM). This phenomenon is a consequence of a decrease in the glucagon-stimulated phosphorylation of phenylalanine hydroxylase from liver cells incubated in the presence of insulin. The impact of insulin on the phosphorylation state and activity of the hydroxylase is mimicked by incubation of liver cells in the presence of orthovanadate (10 microM). A series of cyclic AMP and cyclic GMP analogues enhanced phenylalanine hydroxylation: in each case insulin diminished the stimulation of flux. These results are discussed in the light of the characteristics of insulin action on other metabolic processes.

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Phenylalanine hydroxylase levels in diabetic rats

Cited by 7 publications

References 3 publications

Impact of experimental diabetes on phenylalanine hydroxylase expression in rat liver

Impact of experimental diabetes on phenylalanine hydroxylase expression in rat liver

Effects of starvation on rat phenylalanine hydroxylase activities

The role of insulin in the modulation of glucagon-dependent control of phenylalanine hydroxylation in isolated liver cells

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