ATP sulfurylase from Penicillium chrysogenum: is the internal level of the enzyme sufficient to account for the rate of sulfate utilization?
J Bacteriol, 1979/1;137(1):350-6.
Farley JR, Mayer S, Chandler CJ, Segel IH
PMID: 104967
Impact factor: 3.476
Abstract
The in vivo rate of sulfate activation in Penicillium chrysogenum (wild-type strain ATCC 24791) was determined to be 0.19 +/- 0.09 mumol g(-1) (dry weight) min(-1) by the following methods. (i) The maximum growth of the organism in synthetic medium was a linear function of the initial Na(2)SO(4) concentration between 0 and 8 x 10(-4) Na(2)SO(4). The growth yield was 1.64 x 10(-2) g (dry weight) of mycelium per mumol of added sulfate, corresponding to a minimum sulfur requirement of 61 mumol/g (dry weight). Under these conditions (limiting sulfate) the minimum doubling time of P. chrysogenum in submerged culture was about 3.8 h, corresponding to a maximum exponential growth rate constant of 3.0 x 10(-3) min(-1). If all the sulfur in this mycelium passed through adenosine-5'-phosphosulfate, the rate of sulfate activation in vivo must have been 0.183 mumol min(-1) g(-1) (dry weight). (ii) In the presence of excess (35)SO(4) (2-), the total organic (35)S produced varied with the mycelial growth rate. However, until the culture approached maximum density, the product of [(growth rate constant) x (organic (35)S content)] was nearly constant at 0.24 to 0.28 mumol min(-1) g(-1) (dry weight). (iii) A sulfur-starved mycelium pulsed with 10(-4) M (35)SO(4) (2-) produced organic (35)S at a rate of about 0.10 mumol min(-1) g(-1) (dry weight) under conditions where the internal concentrations of ATP and sulfate would permit ATP sulfurylase to operate at about 70% of its V(max). Cell-free extracts of P. chrysogenum growing rapidly on excess sulfate contained 0.22 U of ATP sulfurylase per g (dry weight). Thus, in spite of the relatively low specific activity of homogeneous ATP sulfurylase (0.13 U/mg of protein, corresponding to an active site turnover of 7.15 min(-1)), the mycelial content of the enzyme was sufficient to account for the observed growth rate of the organism on inorganic sulfate as the sole sulfur source.
MeSH terms
Biological Transport, Active; Kinetics; Nucleotidyltransferases; Penicillium; Penicillium chrysogenum; Sulfate Adenylyltransferase; Sulfates
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