Studies on the enzymology of fat foramtion in beef cattle may lead to the development of a marker for predicting the propensity of these animals to deposit intramuscular (i.m.) fat. Diacylglycerol acyltransferse (DFAT, EC 2.3.1.20) catalyzes the acylation of sn-1,2-diacylglycerol to form triacylglycerol (TAG). This thesis has focused on evaluating DGAT as a potential marker for predicting i.m. fat deposition in cattle and on characterization of the enzyme in three tissue types involved in TAG biosynthesis. Microsomes were isolated from subcutaneous (s.c.) adipose, i.m. adipose and muscle tissue of Wagyu crossbred cattle displaying a wide range of i.m. fat content (marbling). One aspect of this thesis focused on the relationship between total lipid present in meat samples from the pars costalis diaphragmatis (p.c.d.) and DGAT activity from s.c. adipose tissue, i.m. adipose tissue and muscle tissue of the p.c.d. Intramuscular adipose tissue DGAT activity exhibited a negative correlation with % TAG per gram wet weight p.c.d. (r=-.547;P<.01). There was, however, a positive correlation (r=.735;P<.001) between DGAT activity per unit wet weight i.m. adipose tissue and muscle DGAT activity per unit wet weight suggesting these two depots are coordinated in terms of TAG biosynthetic capacity. The second aspect of the thesis exmained the characteristics of microsomal DGAT from the three tissue types. Microsomes from several animals were combined and were used for enzymological studies of DGAT in an attempt to define possible differences in enzymatic properties among the three tissue types. Diacylglycerol acyltransferase from s.c. adipose tissue in the presence of 15 mM MgCl2 exhibited an enhanced preference for substrates containing oleoyl moieties relative to the other two tissue types. Diacylglycerol acyltransferase from s.c. adipose tissue alos differed slightly in sensitivity to N-ethylmaleimide and stability when compared to the other two tissues, muscle and i.m. adipose tissue. Collectively, these results suggested that either a different isoform of DGAT is expressed in s.c. adipose tissue as compared to i.m. adipose and muscle tissue, or that the endoplasmic reticulum micro-environments are sufficiently different to account for the depot specific properties of DGAT in bovine. The data presented in this thesis suggested that DGAT was not a suitable marker for the deposition of i.m. fat in mature cattle. Perhaps an examination of i.m. fat deposition in less mature animals will yield stronger, positive correlations between DGAT activity and the amount of i.m. fat present. / xvi, 109 leaves : ill. ; 28 cm.

Peroxisome proliferator-activated receptor (PPARy) is a transcription factor that regulates adipogenic genes and preadipocyte factor-1 (pref-1) is a transmembrane protein that regulates preadipocyte differnetiation. The role of PPARy was investigated using reverse transcription polymerase chain reaction (RT-PCR) by measuring PPARy mRNA levels in bovine adipose depots and longissimus dorsi muscle. No significant differences in PPARy mRNA levels were observed between 10 Charolais and 10 Holstein cattle for either tissue. Differences were observed between depots within these breeds. Correlations were performed among PPARy, carcass characteristics, and adipogenic genes. Pref-1 antibodies were used to immunolocate preadipocytes in bovine muscle tissue to the perimycium, near fat cells and blood vessels. The preadipocytes may exist in muscle tissue for short periods of time or may arise from a source external to the muscle. A computer image analysis program was developed for the quanitifaction and characterization of intramuscular fat in whole muscle tissues. / xvi, 154 leaves : ill. (some col.) ; 28 cm.