Interrelationships of tubulin-GDP and tubulin-GTP in microtubule assembly

Journal Article · Tue Nov 03 04:00:00 EST 1987 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00396a045· OSTI ID:5562478

Lin, C M; Hamel, E

The author previously reported that direct incorporation of GDP (i.e., without an initial hydrolysis of GTP) into microtubules occurs throughout an assembly cycle in a constant proportion. The exact proportion varied with reaction conditions, becoming greater under all conditions in which tubulin-GDP increased relative to tubulin-GTP (low Mg/sup 2 +/ and GTP concentrations, high tubulin concentrations, and in the presence of exogeneous GDP). These findings led the authors to explore further interrelationships of tubulin-GDP and tubulin-GTP in microtubule assembly. They have now determined the minimum amount of tubulin-GTP required for the initiation of microtubule assembly and the relative efficiency with which tubulin-GDP participates in microtubule elongation. When (8-/sup 14/C)GTP, (8-/sup 14/C)GDP, and tubulin concentrations were varied at a constant Mg/sup 2 +/ concentration (0.2 mM), initiation of assembly required that 35% of the nucleotide-bearing tubulin be in the form of tubulin-GTP, and incorporation of tubulin-GDP into microtubules during elongation was only 60% as efficient as would be predicted on the basis of its proportional concentration in the reaction mixtures. Very different results were obtained when the Mg/sup 2 +/ concentration was varied. In the absence of exogenous Mg/sup 2 +/, only 20% tubulin-GTP was required for initiation, and tubulin-GDP was directly incorporated into microtubules half as efficiently as would be predicted on the basis of its concentration in the reaction mixture. At the highest Mg/sup 2 +/ concentration examined (4 mM), 80% tubulin-GTP was required for initiation of assembly, and tubulin-GDP was incorporated into microtubules as efficiently as tubulin-GTP.

• Research Organization: National Institutes of Health, Bethesda, MD
• OSTI ID: 5562478
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:22; ISSN BICHA
• Country of Publication: United States
• Language: English

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550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH METAL COMPOUNDS
BIOSYNTHESIS
CARBON 14 COMPOUNDS
CELL CONSTITUENTS
CHLORIDES
CHLORINE COMPOUNDS
CONFIGURATION INTERACTION
DOSE-RESPONSE RELATIONSHIPS
GUANYLIC ACID
HALIDES
HALOGEN COMPOUNDS
LABELLED COMPOUNDS
MAGNESIUM CHLORIDES
MAGNESIUM COMPOUNDS
MICROTUBULES
NUCLEOTIDES
ORGANIC COMPOUNDS
PROTEINS
SYNTHESIS