Biochemical characterization of plant biotin-containing enzymes

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Diez, Tomás
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Basil J. Nikolau
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Biochemistry, Biophysics and Molecular Biology

The Department of Biochemistry, Biophysics, and Molecular Biology was founded to give students an understanding of life principles through the understanding of chemical and physical principles. Among these principles are frontiers of biotechnology such as metabolic networking, the structure of hormones and proteins, genomics, and the like.

The Department of Biochemistry and Biophysics was founded in 1959, and was administered by the College of Sciences and Humanities (later, College of Liberal Arts & Sciences). In 1979 it became co-administered by the Department of Agriculture (later, College of Agriculture and Life Sciences). In 1998 its name changed to the Department of Biochemistry, Biophysics, and Molecular Biology.

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  • Department of Biochemistry and Biophysics (1959–1998)

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3-Methylcrotonyl-CoA carboxylase has been purified and characterized from maize leaves. The enzyme is composed of two subunits, a biotin-containing polypeptide of 80 kDa, and a nonbiotin-containing polypeptide of 58 kDa. The native molecular weight of the holoenzyme is estimated at 853,000. The enzyme probably has an [alpha][subscript]6[beta][subscript]6 configuration. The kinetic constants for the substrates of 3-methylcrotonyl-CoA and its pH optimum were determined. The enzyme is allosterically activated by Mg[superscript]2+ and nonessentially activated by monovalent cations. The enzyme is strongly inhibited by acetoacetyl-CoA and by arginyl and sulfhydryl modifying reagents;The effect of K[superscript]+ on 3-methylcrotonyl-CoA carboxylase has been studied. K[superscript]+ affects the binding of ATP and 3-methylcrotonyl-CoA to the enzyme, but does not affect the binding of bicarbonate. The results indicate that K[superscript]+ is involved in the first half-reaction in which the carboxybiotinyl intermediate is formed;Initial velocity studies with competitive inhibitors of soybean 3-methylcrotonyl-CoA carboxylase are consistent with the enzyme following a random Bi Bi Uni Uni Ping Pong mechanism. A rate equation for this mechanism has been deduced;Propionyl-CoA carboxylase activity has been purified from maize leaves. This activity copurified with acetyl-CoA carboxylase activity throughout the purification procedures. Inhibition studies and mixed substrate analyses suggest that propionyl-CoA carboxylase activity detectable in extracts from plants is a side reaction of the acetyl-CoA carboxylase enzyme;Geranoyl-CoA carboxylase has been partially purified and characterized from maize leaves. The kinetic constants for the substrates of the enzyme, geranoyl-CoA, ATP, and bicarbonate, and its pH optimum have been determined. The enzyme occurs ubiquitously through the maize plant. This is the first demonstration of the presence of geranoyl-CoA carboxylase in eukaryotic organisms. A potential metabolic function of this enzyme in the catabolism of monoterpenes is discussed.

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Sat Jan 01 00:00:00 UTC 1994