The rate constant describing slow-onset inhibition of yeast AMP deaminase by coformycin analogues is independent of inhibitor structure

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

(R)- and (S)-2′-deoxycoformycin, (R)-coformycin, and the corresponding 5′-monophosphates were compared as inhibitors of yeast AMP deaminase. The overall inhibition constants ranged from 4.2 mM for (S)-2′-deoxycofonnycin to 10 pM for (R)-coformycin 5′-monophosphate, a difference of 3.8 × 108 in affinities. (R)-Coformycin, (R)-2′-deoxycoformycin S′-monophosphate, and (R)-coformycin 5′-monophosphate exhibited both rapid and slow-onset inhibition. The S inhibitors and (R)-2′-deoxycoformycin exhibited classical competitive inhibition but no time-dependent onset of inhibition. The results indicate that the presence of the 2′-hydroxyl and 5′-phosphate and the R stereochemistry at the C-8 position of the diazepine ring are necessary for the optimum interaction of inhibitors with yeast AMP deaminase. This differs from the results for rabbit muscle AMP deaminase [Frieden C., Kurz, L. C, & Gilbert, H. R. (1980) Biochemistry 19, 5303-5309] and calf intestinal adenosine deaminase [Schramm, V. L., & Baker, D. C. (1985) Biochemistry 24, 641-646], in which a tetrahedral hydroxyl at C-8 in the R stereochemistry is sufficient for slow-onset inhibition with the coformycins. The results suggest that the transition state contains a tetrahedral carbon with the R configuration as a result of the direct attack of an oxygen nucleophile at C-6 of AMP. Slow-onset inhibition of yeast AMP deaminase is consistent with the mechanism E+I⇌KiEI⇌ksk6EI* in which the combination of E and I is rapidly reversible. For these inhibitors, Ki* varied by a factor of 2 × 103, and the overall inhibition constant (Ki*) varied by a factor of 2 × 105. The rate k5, which induces slow-onset inhibition, was similar for the three slow-onset inhibitors while k6 varied by a factor of 650, suggesting that k5 is independent of inhibitor structure. The ability to act as a slow-onset inhibitor is a result of the ability of the inhibitor to stabilize the El* complex. These findings argue against inhibitor-induced transition-state conformations for the slow-onset inhibitors and suggest that the enzyme attains the transition-state configuration at a low rate independent of the inhibitor structure.

Original languageEnglish (US)
Pages (from-to)8358-8364
Number of pages7
JournalBiochemistry®
Volume29
Issue number36
StatePublished - 1990

Fingerprint

Coformycin
AMP Deaminase
Yeast
Pentostatin
Rate constants
Yeasts
Biochemistry
Stereochemistry
Hydroxyl Radical
Nucleophiles
Adenosine Deaminase
Enzyme Inhibitors
Adenosine Monophosphate
Muscle
Conformations
Carbon
Phosphates
Oxygen
Rabbits
Muscles

ASJC Scopus subject areas

  • Biochemistry

Cite this

@article{da36b548f91d40339eb83c97c97b905d,
title = "The rate constant describing slow-onset inhibition of yeast AMP deaminase by coformycin analogues is independent of inhibitor structure",
abstract = "(R)- and (S)-2′-deoxycoformycin, (R)-coformycin, and the corresponding 5′-monophosphates were compared as inhibitors of yeast AMP deaminase. The overall inhibition constants ranged from 4.2 mM for (S)-2′-deoxycofonnycin to 10 pM for (R)-coformycin 5′-monophosphate, a difference of 3.8 × 108 in affinities. (R)-Coformycin, (R)-2′-deoxycoformycin S′-monophosphate, and (R)-coformycin 5′-monophosphate exhibited both rapid and slow-onset inhibition. The S inhibitors and (R)-2′-deoxycoformycin exhibited classical competitive inhibition but no time-dependent onset of inhibition. The results indicate that the presence of the 2′-hydroxyl and 5′-phosphate and the R stereochemistry at the C-8 position of the diazepine ring are necessary for the optimum interaction of inhibitors with yeast AMP deaminase. This differs from the results for rabbit muscle AMP deaminase [Frieden C., Kurz, L. C, & Gilbert, H. R. (1980) Biochemistry 19, 5303-5309] and calf intestinal adenosine deaminase [Schramm, V. L., & Baker, D. C. (1985) Biochemistry 24, 641-646], in which a tetrahedral hydroxyl at C-8 in the R stereochemistry is sufficient for slow-onset inhibition with the coformycins. The results suggest that the transition state contains a tetrahedral carbon with the R configuration as a result of the direct attack of an oxygen nucleophile at C-6 of AMP. Slow-onset inhibition of yeast AMP deaminase is consistent with the mechanism E+I⇌KiEI⇌ksk6EI* in which the combination of E and I is rapidly reversible. For these inhibitors, Ki* varied by a factor of 2 × 103, and the overall inhibition constant (Ki*) varied by a factor of 2 × 105. The rate k5, which induces slow-onset inhibition, was similar for the three slow-onset inhibitors while k6 varied by a factor of 650, suggesting that k5 is independent of inhibitor structure. The ability to act as a slow-onset inhibitor is a result of the ability of the inhibitor to stabilize the El* complex. These findings argue against inhibitor-induced transition-state conformations for the slow-onset inhibitors and suggest that the enzyme attains the transition-state configuration at a low rate independent of the inhibitor structure.",
author = "Merkler, {David J.} and Brenowitz, {Michael D.} and Schramm, {Vern L.}",
year = "1990",
language = "English (US)",
volume = "29",
pages = "8358--8364",
journal = "Biochemistry",
issn = "0006-2960",
publisher = "American Chemical Society",
number = "36",

}

TY - JOUR

T1 - The rate constant describing slow-onset inhibition of yeast AMP deaminase by coformycin analogues is independent of inhibitor structure

AU - Merkler, David J.

AU - Brenowitz, Michael D.

AU - Schramm, Vern L.

PY - 1990

Y1 - 1990

N2 - (R)- and (S)-2′-deoxycoformycin, (R)-coformycin, and the corresponding 5′-monophosphates were compared as inhibitors of yeast AMP deaminase. The overall inhibition constants ranged from 4.2 mM for (S)-2′-deoxycofonnycin to 10 pM for (R)-coformycin 5′-monophosphate, a difference of 3.8 × 108 in affinities. (R)-Coformycin, (R)-2′-deoxycoformycin S′-monophosphate, and (R)-coformycin 5′-monophosphate exhibited both rapid and slow-onset inhibition. The S inhibitors and (R)-2′-deoxycoformycin exhibited classical competitive inhibition but no time-dependent onset of inhibition. The results indicate that the presence of the 2′-hydroxyl and 5′-phosphate and the R stereochemistry at the C-8 position of the diazepine ring are necessary for the optimum interaction of inhibitors with yeast AMP deaminase. This differs from the results for rabbit muscle AMP deaminase [Frieden C., Kurz, L. C, & Gilbert, H. R. (1980) Biochemistry 19, 5303-5309] and calf intestinal adenosine deaminase [Schramm, V. L., & Baker, D. C. (1985) Biochemistry 24, 641-646], in which a tetrahedral hydroxyl at C-8 in the R stereochemistry is sufficient for slow-onset inhibition with the coformycins. The results suggest that the transition state contains a tetrahedral carbon with the R configuration as a result of the direct attack of an oxygen nucleophile at C-6 of AMP. Slow-onset inhibition of yeast AMP deaminase is consistent with the mechanism E+I⇌KiEI⇌ksk6EI* in which the combination of E and I is rapidly reversible. For these inhibitors, Ki* varied by a factor of 2 × 103, and the overall inhibition constant (Ki*) varied by a factor of 2 × 105. The rate k5, which induces slow-onset inhibition, was similar for the three slow-onset inhibitors while k6 varied by a factor of 650, suggesting that k5 is independent of inhibitor structure. The ability to act as a slow-onset inhibitor is a result of the ability of the inhibitor to stabilize the El* complex. These findings argue against inhibitor-induced transition-state conformations for the slow-onset inhibitors and suggest that the enzyme attains the transition-state configuration at a low rate independent of the inhibitor structure.

AB - (R)- and (S)-2′-deoxycoformycin, (R)-coformycin, and the corresponding 5′-monophosphates were compared as inhibitors of yeast AMP deaminase. The overall inhibition constants ranged from 4.2 mM for (S)-2′-deoxycofonnycin to 10 pM for (R)-coformycin 5′-monophosphate, a difference of 3.8 × 108 in affinities. (R)-Coformycin, (R)-2′-deoxycoformycin S′-monophosphate, and (R)-coformycin 5′-monophosphate exhibited both rapid and slow-onset inhibition. The S inhibitors and (R)-2′-deoxycoformycin exhibited classical competitive inhibition but no time-dependent onset of inhibition. The results indicate that the presence of the 2′-hydroxyl and 5′-phosphate and the R stereochemistry at the C-8 position of the diazepine ring are necessary for the optimum interaction of inhibitors with yeast AMP deaminase. This differs from the results for rabbit muscle AMP deaminase [Frieden C., Kurz, L. C, & Gilbert, H. R. (1980) Biochemistry 19, 5303-5309] and calf intestinal adenosine deaminase [Schramm, V. L., & Baker, D. C. (1985) Biochemistry 24, 641-646], in which a tetrahedral hydroxyl at C-8 in the R stereochemistry is sufficient for slow-onset inhibition with the coformycins. The results suggest that the transition state contains a tetrahedral carbon with the R configuration as a result of the direct attack of an oxygen nucleophile at C-6 of AMP. Slow-onset inhibition of yeast AMP deaminase is consistent with the mechanism E+I⇌KiEI⇌ksk6EI* in which the combination of E and I is rapidly reversible. For these inhibitors, Ki* varied by a factor of 2 × 103, and the overall inhibition constant (Ki*) varied by a factor of 2 × 105. The rate k5, which induces slow-onset inhibition, was similar for the three slow-onset inhibitors while k6 varied by a factor of 650, suggesting that k5 is independent of inhibitor structure. The ability to act as a slow-onset inhibitor is a result of the ability of the inhibitor to stabilize the El* complex. These findings argue against inhibitor-induced transition-state conformations for the slow-onset inhibitors and suggest that the enzyme attains the transition-state configuration at a low rate independent of the inhibitor structure.

UR - http://www.scopus.com/inward/record.url?scp=0025118703&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0025118703&partnerID=8YFLogxK

M3 - Article

C2 - 2252896

AN - SCOPUS:0025118703

VL - 29

SP - 8358

EP - 8364

JO - Biochemistry

JF - Biochemistry

SN - 0006-2960

IS - 36

ER -