Direct Desaturation of Free Myristic Acid by Hen Liver Microsomal Δ⁹-Desaturase without Prior Activation to Myristoyl-CoA Derivative

Abstract

Direct desaturation of free myristic acid by hen liver microsomal Delta(9)-desaturase without prior activation to myristoyl-CoA by the addition of adenosine triphosphate (ATP) and CoA was observed when the incubation medium was mixed at mixing speeds of >250 rpm in the presence of fatty acid-binding proteins (FABP). Desaturation was linear with time and proportional to the microsomal protein concentration. Desaturation was maximal at pH 7.9. The greatest desaturation rate was observed at a mixing speed of 500 rpm in the presence of FABP. Desaturation decreased at mixing speeds of >500 rpm. Data suggest that when myristic acid is bound to FABP in the form of protein-monomer complexes, its activation to the CoA derivative is not necessary for it to be desaturated by the Delta(9)-desaturase when using mixing rates of >250 rpm. Myristic acid-FABP complexes serve as substrates for the Delta(9)-desaturase at mixing rates of >250 rpm. Desaturation was reduced by bovine serum albumin and alpha-bromohexadecanoate, and no desaturation was observed in the absence of FABP. These findings suggest that FABP may regulate the accessibility of fatty acids in the desaturation reaction to the active site of the desaturase rather than just protect the membrane-bound desaturase from the cytotoxic effect of free fatty acids.

Gene networks driving bovine milk fat synthesis during the lactation cycle

“…In addition to a trafficking role, FABP3 through binding of activated acyl-CoAs could buffer cells from negative effects of activated FA and prevent inhibition of ACACA and SCD (stearoyl-CoA desaturase), roles usually attributed to ACBP [ 39 ]. A positive relationship between FABP and SCD has been demonstrated in chickens [ 41 ], indicating a coordinated function between both proteins in mammary tissue as also suggested previously from an evaluation of published data [ 6 ]. Based on our longitudinal mRNA expression and fatty acid data we propose that an important function of FABP3 in bovine mammary is to provide FA for SCD.…”

Transcriptome expression analysis of candidate milk genes affecting cheese-related traits in 2 sheep breeds

“…The more highly expressed gene, H-FABP, encodes the FA binding protein, and in addition to its trafficking role, this protein has been shown to prevent the inhibition of ACACA and SCD (Faergeman et al, 2007), which are genes related to de novo FA synthesis and desaturation. Previous studies in chicken and cow have associated H-FABP expression with SCD (Awad et al, 2004;Bionaz and Loor, 2008), suggesting that H-FABP provides FA for SCD, which then releases oleic acid (Bionaz and Loor, 2008). However, in this study, expression levels for H-FABP were higher in Assaf sheep, and the FPKM values for SCD were higher in Churra sheep (Figure 1b).…”