Biomedical subjects

H Semb

Publications and source records attributed to H Semb.

At least 37 records · Page 2Linked to original sources

PubMed1987

Molecular cloning and sequence analysis of cDNA encoding lipoprotein lipase of guinea pig.

We have isolated and sequenced cDNA clones covering the entire coding sequence and short flanking regions of guinea pig lipoprotein lipase. The expression cDNA library used was constructed in lambda gt11 with mRNA derived from adipocytes. The deduced amino acid (aa) sequence starts with a stretch of 17 aa interpreted as a leader peptide. The open reading frame continues with 448 aa residues and ends with a TGA stop codon. Combined with previous data this information allows the assignment of domains in the lipase molecule. A likely candidate for the heparin-binding site is a 9-aa stretch containing five positive charges, analogous to the consensus sequence for receptor-binding sites on apolipoproteins E and B. A previously noted homology to pancreatic lipase is extended. Analysis of polyadenylated RNA from several tissues indicated a high level of expression in adipocytes, heart muscle and mammary gland. No lipoprotein lipase mRNA could be detected in liver. Northern blots revealed three major mRNAs with sizes corresponding to 3.8 kb, 3.3 kb and 2.1 kb, respectively. In adipocytes and heart muscle a fourth mRNA, with an estimated size of 4.5 kb, was also detected. Analysis of genomic DNA by Southern blotting indicated a single gene locus coding for lipoprotein lipase. Hence, modification of the primary transcript seems to be involved in the production of the various mRNAs.

Amino Acid Sequence↗

PubMed1986

Lipoprotein lipase in guinea pig tissues: molecular size and rates of synthesis.

Lipoprotein lipase was immunoprecipitated from guinea pig tissues which had been pulse labeled with [35S]methionine. The apparent size of the product (on SDS gels) was 55 kDa in all tissues studied. Lipoprotein lipase released by heparin from adipocytes and from perfused hearts had the same apparent size. No significant amounts of immunoreactive protein with smaller size were found on immunoblotting of tissue homogenates, or in preparations partially purified by heparin-Sepharose chromatography. Lipoprotein lipase accounted for only a small proportion of total protein synthesis. The highest value was in adipose tissue (0.3-0.8%). In lactating mammary gland lipoprotein lipase accounted for about 0.1%, a figure similar to that previously estimated for the proportion of lipoprotein lipase protein in milk. This suggests that lipoprotein lipase is secreted into milk as efficiently as other milk proteins are, in contrast to the previous opinion that the enzyme appears in milk because small amounts leak out from tissue sites. Relative synthesis of lipoprotein lipase was the same in adipocytes from fed or fasted animals, whereas relative synthesis of several other proteins changed dramatically. This indicates that some proteins in guinea pig adipose tissue are under transcriptional control in response to feeding-fasting, but that lipoprotein lipase is not.

Adipose Tissue↗

PubMed1986

Nutritional regulation of lipoprotein lipase in guinea pig tissues.

Glucose transport in guinea pig adipocytes has been shown to be markedly resistant to stimulation by insulin. Lipoprotein lipase is another transport catalyst in adipose tissue which is believed to be regulated by insulin. We have therefore studied how feeding-fasting affects lipoprotein lipase activity in guinea pig tissues. There was an even more marked decrease in adipose tissue lipoprotein lipase activity on fasting in guinea pigs (10-20 fold) than in rats or mice (4-5 fold). In adipocytes, the activity decreased only 2.5-4.5 fold; most of the change was in extracellular lipoprotein lipase. On glucose refeeding, the activity was rapidly restored. In the first 4 hours after glucose administration extracellular lipoprotein lipase activity increased to more than 10 times the amount present in adipocytes. After cycloheximide, lipoprotein lipase activity decreased with a half-life of 22 min. It is concluded that lipoprotein lipase is rapidly produced and turned over in guinea pig adipose tissue, and that the system is quite sensitive to feeding-fasting. In contrast to adipose tissue, there was no significant change in lipoprotein lipase activity in any other tissue on fasting. There was a strong correlation between the activities in heart and diaphragm muscle, but this correlation was independent of feeding-fasting.

Adipose Tissue↗

PubMed1972