Inhibition of Carbonic Anhydrase by Thiocyanate See MC(;EI(:HIN,R.L., J . Chem. Educ., 32,101-2 (1955).
Cnrhonic anhydrase, an enzyme which is present in animal (including human) blood, catalyzes the decomposition of carbonic acid to carbon dioxide and water. Like other enaymrs, it is inhibited, to a greater or lesser degree, by many substances. For c ~ a m p l in ~ , the presence of thiocyanate ion, the catalytic action of carbonic anhyrlrase is reduced, m d this inhihition increases as the ronrentmtion of thiocyanate ion is increased. Mdkwchin has s t u d i d the effect of thiocynnate ion on the rste:of the reaction COr
+ HzO
-
H?CO,
which is also catalyzed by cnrhonic snhydrase. The reaction was iollowed by noting the time required far bromthsmol blue to "hang? color when COI was bubbled a t a reproducible ratc into 3 mixture of aqueous buffer, blood, hromthymol blue, and thiocyanate ion in vnrj-ing concentrations.
Oueslionr: Can sstisfaetary determinations of the inhibitory effect of thincyanate ion on carbonic anhydrase he obtained by modifying Mctiearhin's procedure, using ar small piece of dry ice (ahout 0.5 mi volume) inserted directly into the aqueous mixture, instead of using CO* from a tank of compressed gas or n Icipp generator? What other substances can you find which inhihit the mtalytic .,tion carbonic anhydrsse? their quantitatively if possible, with thiooyanatebn. Is the quantity of carbonic snhydrsse, present in equal volumes, the same far many different kinds of animal blood? Does the concentration of carbonic anhydrase present in !-our just prior to blood vary with the vigor f, extracting the sample of blood to be examined? If so, suggest an explanation and test by further lsharatory work. Is carbonic anhydrase present in a chloroform extract of r ~ d blood cells?
compare
Volume 38, Number 9, September 1961
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