The effect of displacement current on the measurement of reversal potential in squid giant axon

The measurement of the sodium reversal potential (Erev), as that potential where the early current reverses during voltage clamp, was found to exceed the true Erev by 4.1 +/- 2.4 mV (mean +/- SD) in squid giant axon. This error was found in both intact and internally perfused axons and is due to interference from the displacement current. This was shown by subtraction of the current records obtained before and after treatment with tetrodotoxin (TTX). The error in Erev is proportional to (Td/gNA)12 where Td is the time constant of the displacement current.     

Identification of a cell cycle-dependent gene product as a sialic acid-binding protein

A Ca2+-dependent sialic acid-binding protein was purified on fetuin-Sepharose from various types of human tissue. The molecular mass was determined to be 10,315 Da by laser desorption mass spectrometry. Partial sequence analysis after cyanogen bromide cleavage that yielded one N-terminus accessible for Edman degradation revealed an identity to an internal stretch following the only methionine residue within a putative amino acid sequence (Mr 10,048), deduced from the cDNA of a cell cycle-specific gene. The reported biochemical identification is a prerequisite to infer the biological role of the so far undetected gene product. Initial glycohistochemical studies with sialic acid-(BSA-biotin) raised evidence for nuclear localization of sialic acid-binding sites that might reflect, at least in part, detection of this protein.     

The fully-active nature of synthetic and hydrolytic activities of glucose-6-phosphatase of intact nuclear membrane

Carbamyl-P: glucose phosphotransferase, mannose-6-P: glucose phosphotransferase, and mannose-6-P and glucose-6-P phosphohydrolase activities of D-glucose-6-P phosphohydrolase (EC 3.1.3.9) have been demonstrated in avian and mammalian liver (and kidney) nuclear membrane. In marked contrast with activities of this enzyme of fragmented endoplasmic reticulum (“microsomes”), those of the intact membrane of isolated nuclei are totally, or nearly-totally, manifest without the need for preliminary activation by detergents or similar treatments. Disruption of nuclei and isolation of nuclear membranes results in the acquisition of detergent-sensitivity of such activities. Physiological implications of these observations are discussed.