Peptide and Protein Synthesis. Protein Turnover

Tarver, Harold

doi:10.1016/b978-0-12-395721-4.50012-3

Cited by 30 publications

(7 citation statements)

References 311 publications

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“…This method of estimating the secretion rate of a hormone depends on the following assumptions (Zilversmit, Entenman & Fishier, 1943;Tarver, 1954): (1) The dis¬ appearance of labelled hormone is due only to secretion and there is no degradation of the hormone within the gland. (2) The gland is in a steady state.…”

Section: Introductionmentioning

confidence: 99%

Prolactin Turnover in Rat Adenohypophyses in Vivo: Its Evaluation as a Method for Estimating Secretion Rates

Swearingen¹,

Nicoll²

1972

Journal of Endocrinology

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The kinetics of prolactin turnover were investigated in female rat adenohypophyses in vivo. The animals received an intravenous injection of [3H]leucine and groups were killed at various times thereafter. The prolactin in their adenohypophyses was separated and measured by disc electrophoresis and densitometry. The hormone band was cut from the gel columns and counted by liquid scintillation procedures. The specific activity data (c.p.m./\g=m\g) were fitted to single or double exponential functions by the method of least squares, using a computer program. The slow component of the double exponential, or the single component of the single exponential were assumed to represent secretion and their rate constants were multiplied by the hormone content of the gland to obtain an estimate of secretion rate. The assumptions involved in this method of estimating secretion rates are discussed and evaluated.The rate constant for prolactin in oestrogen + reserpine-treated females (0\ m=. \ 10\ p=n-\ 0\ m=. \ 08 h\ m=-\ 1) was higher than that obtained in rats treated with oestrogen alone (0\ m=. \ 05\ p=n-\ 0\ m=. \ 06), and approximately three times that in rats treated with reserpine only (0\m=.\03). The prolactin concentration in the adenohypophysis was highest in reserpine-treated rats (8\ m=. \ 2 \g=m\g/mg) while in glands from oestrogen-treated ( 4\ m=. \ 1\ p=n-\ 6\ m=. \ 0 \g=m\g/mg) and oestrogen + reserpine-treated animals ( 5\ m=. \ 0\ p=n-\ 6\ m=. \ 2 \g=m\g/mg) it was similar. The average prolactin secretion rates in oestrogen-treated (0\m=.\26 \ g = m\ g / mg / h ) and reserpine-treated (0\m=.\25 \ g = m\ g / mg / h rats were similar, while the average rate in reserpine + oestrogen-treated rats (0\m=.\54 \ g = m\ g / mg / h ) was twice as high. The results with reserpine-treated animals (low rate constant, high gland content), with oestrogen + reserpine-treated animals (high rate constant), and of those previously obtained by us in ectopic adenohypophysial transplants (high rate constant, low gland content) are discussed in terms of possible involvement of a prolactin stimulating factor. It is concluded that this method provides useful estimates of secretion rates as well as information on the intrapituitary turnover of prolactin.

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Section: Introductionmentioning

confidence: 99%

Prolactin Turnover in Rat Adenohypophyses in Vivo: Its Evaluation as a Method for Estimating Secretion Rates

Swearingen¹,

Nicoll²

1972

Journal of Endocrinology

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“…From these data the half-life (ti) of the cellular proteins during growth was obtained. The turnover time (tt) of the proteins was calculated from the relationship: tt = tg/ln 2 (Tarver, 1954 Protein breakdown under non-growing conditions. The organism was grown for several generations in medium containing [l*C]leucine.…”

Section: T P Coultate T K S U N D a R A M A N D J J C A Z Z U L Omentioning

confidence: 99%

Stability of Protein and Ribonucleic Acid in Bacillus stearothermophilus

Coultate

Sundaram

Cazzulo

1975

Journal of General Microbiology

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The turnover of protein in a prototrophic strain of Bacillus stearothermophilus during exponential growth in a salts medium with glucose or succinate as carbon source was about 4 %/h and in a richer nutrient broth medium about 23 %/h. Protein degradation under non-growing conditions conformed to a similar pattern. The turnover of RNA (non-messenger) was about I %/h in salts medium and about g %/h in nutrient broth. The turnover of protein and R N A in the thermophile is thus moderate rather than massive. This conclusion was confirmed by measurement of the decay of a specific enzyme, isocitrate lyase, in the prototroph and of the overall protein turnover in a non-prototrophic strain of B. stearothermophilus. The half-lives of a number of enzyme systems in intact cells of the prototrophic thermophile at its optimum growth temperature showed some variation but indicated a significant rate of inactivation. Such decay of protein in vivo apparently accounts for the moderate protein turnover observed during growth. I N T R O D U C T I O NThe rate of turnover of proteins, and also of nucleic acids (other than mRNA), is very low (less than I %/h) in mesophilic bacteria during exponential growth and somewhat higher (up to 5 %/h) under non-growing conditions (Mandelstam, 1960; Halvorson, 1962). Protein turnover in the absence of growth appears to occur in these organisms in response to conditions in which synthesis of new proteins takes place in nutritionally deprived environments, such as in sporulation (Mandelstam & Waites, 1968) and the intermediate lag phase of diauxic growth (Halvorson, 1962). A different function for protein turnover in thermophilic micro-organisms was envisaged by Allen's (1 953) hypothesis that thermophiles compensate for the breakdown of macromolecules, particularly proteins, at their high growth temperatures by rapid resynthesis. Although this theory has now been overshadowed by the finding that thermophile proteins are invariably more thermostable than their mesophilic counterparts, there is apparently no agreement on the question of the extent of protein turnover in thermophilic organisms (Goldberg & Dice, 1974). Thus Bubela & Holdsworth (1966) reported exceedingly rapid protein turnover in Bacillus stearothermophilus, suggesting that this result lent support to Allen's idea; Epstein & Grossowicz (1969b), on the other hand, observed that the rate of protein turnover in their prototrophic strain of B. stearothermophilus was similar to that found in mesophiles.We examined the degradation of macromolecules, particularly proteins, in B. stearo-* Present address :

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“…The neutralized solution was concentrated and glycine in the solution was precipitated by ethanol. 6. Estimation of the radioactivity of the isolated glycine.…”

Section: * Present Adress: Research Laboratory Of Aminomentioning

confidence: 99%