On the effects of cyanide on phenoxazinone synthetase

TY - JOUR

T1 - On the effects of cyanide on phenoxazinone synthetase

AU - Nishimura, Jonathan S.

AU - Golub, Ellis G.

N1 - Funding Information: Cu 2+ to the assay solution, as shown in Fig. I. The reversing effect due to Cu 2+ cannot be simply ascribed to complexing of most of the cyanide by the metal ion, since cyanide was present in a 9-fold molar excess with respect to Cu 2+. Cu + was as effective as Cu ~+. A variety of other metal ions was tested but none was found to simulate the effects caused by copper ions. These included Ca 2+, Mn =+, Mg 2+, Fe ~+, Fe a+, Cr a+ and Co 2+. When the dialysis against cyanide was conducted at an enzyme concentration Io-fold greater than that used in the experiments just described, no significant effects on the kinetics were observed, even after IOO h of exposure. Neither cyanide nor EDTA at IlO -4 M is a potent inhibitor of phenoxazinone synthetase. However, we have found that preincubation of the enzyme with cyanide can lead to sensitization of the enzyme to EDTA. This is illustrated in Fig. 2. Relatively short preincubation with o.oi M cyanide led to significant losses of phenoxazinone synthetase activity, when the enzyme was assayed in the presence of I • lO -4 M EDTA. These were actual losses of apparent activity and were not caused by lengthening of the lag phase. However, the sensitivity of the enzyme to EDTA could be reversed by dialyzing the enzyme to remove cyanide. In these experiments the effects could be evoked at higher enzyme concentrations as well. The results described in this communication indicate that cyanide treatment of phenoxazinone synthetase led to the evolution of two apparent forms of the enzyme: one was normal kinetically, but was EDTA sensitive, and the other was abnormal kinetically as well as EDTA sensitive. The effect of copper ions in restoring normal kinetics does not prove that the enzyme is a copper protein, but a specificity for copper in this action would appear to be indicated. Since dialysis against water reverses the effects of cyanide, it is desirable to study the metal content of the enzyme. In addition, physicochemical studies are needed to see if any correlations may be drawn between the results described here and states of aggregation of the enzyme. The enzyme appears to exist in multiple forms under certain conditions ~. The support of the National Institutes of Health (Grant AI-o6366), the National Science Foundation (Grant GB 8083) and the Tufts University Cancer Committee is acknowledged. Funding Information: This work was supported by grants from the National Science Foundation (GB-7396) and National Institutes of Health (5 ROIAI 03866-08). One of the authors (H.C.R.) is a Research Career Development Awardee of National Institutes of Health (K3-AI-6928).

PY - 1969/12/9

Y1 - 1969/12/9

UR - http://www.scopus.com/inward/record.url?scp=0014628089&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0014628089&partnerID=8YFLogxK

U2 - 10.1016/0005-2744(69)90369-6

DO - 10.1016/0005-2744(69)90369-6

M3 - Article

C2 - 4983242

AN - SCOPUS:0014628089

VL - 191

SP - 724

EP - 726

JO - BBA - Enzymology

JF - BBA - Enzymology

SN - 0005-2744

IS - 3

ER -