Pectin lyase production by recombinant Penicillium griseoroseum strain 105

Recombinant Penicillium griseoroseum strain 105 overproduces an extracellular pectin lyase (PL) under the transcriptional control of the strong gpdA promoter of Aspergillus nidulans . Our aim was to evaluate PL production by recombinant P. griseoroseum strain 105 in submerged fermentation system bioreactors BioFloIII and BioFloIV using 2 or 10 L working volumes under different growth conditions and to analyze the production of cellulase, polygalacturonase, pectin methylesterase, and protease. PL overproduction by recombinant P. griseoroseum strain 105 was 112 times higher than that of P. griseoroseum PG63 grown in sugarcane juice. Cellulases and proteases were not detected in the culture filtrate, and evaluation for extracellular proteins in the culture medium by SDS–PAGE showed the presence of a 36 kDa predominant band, similar to the molecular mass estimated from the nucleotide sequence of plg1 gene for PL of P. griseoroseum strain 105. This recombinant strain provides the advantage of PL production, which predominates over other extracellular proteins usually present in most commercial pectinase preparations, using sugarcane juice as a substrate of low cost.

Decreased transcription of the sodium-phosphate transporter gene in the hypophosphatemic mouse

Recently, it has been hypothesized that the proximal tubular Na(+)-Pi transporter may play a role in murine X-linked hypophosphatemic vitamin D-resistant rickets. In the present investigation, Western blot analysis of renal brush-border membrane proteins, utilizing polyclonal antisera raised against the mouse Na(+)-Pi transporter, revealed a predominant band at 87 kDa in normal and hypophosphatemic (Hyp) mice. The intensity of this band was reduced in the Hyp mouse by 4.5-fold (Hyp/normal = 0.22 +/- 0.04, n = 3, P < 0.05). Additionally, immunohistochemical analysis of kidney cortex in both mice localized the protein to the apical membrane of the proximal tubules. Relative transcription rates of the Na(+)-Pi transporter gene in the normal and Hyp mouse were then investigated. Nuclear run-on assays showed a 51 +/- 0.02% decreased rate of transcription of the Na(+)-Pi transporter gene in the Hyp mice (n = 3). Thus abnormal transcriptional control of this gene in the Hyp mouse likely plays a role in X-linked hypophosphatemia.

The structure of the hepatic insulin receptor and insulin binding

Hepatocytes or hepatic plasma membranes were photoaffinity-labelled with radioiodinated N epsilon B29-monoazidobenzoyl-insulin. Analysis of the samples by SDS/polyacrylamide-gel electrophoresis and autoradiography revealed the insulin receptor as a predominant band of 450 kDa. When hepatic plasma membranes were first treated with clostridial collagenase and then photolabelled, the insulin receptor appeared as a predominant band of 360 kDa. This effect of collagenase treatment on the insulin receptor was due to Ca2+-dependent heat-labile proteinases contaminating the preparation of collagenase, and it could be mimicked by elastase. The decrease in size of the insulin receptor to 360 kDa resulted from the loss of a receptor component that was inaccessible to photolabelling. In contrast, the size of the insulin receptor of intact cells was not affected by collagenase treatment. This suggests that the site sensitive to proteolysis was located on the cytoplasmic side of the plasma membrane. In hepatic plasma membranes that were treated with collagenase or elastase, and contained the 360 kDa form of the insulin receptor, the binding affinity for insulin was increased by up to 2-fold. These findings support the concept that a component which is either a part of, or closely associated with, the insulin receptor may regulate its affinity for insulin.