The molecular cloning of carcinoembryonic antigen (CEA) and several cross-reacting antigens reveals a basic domain structure for the whole family, which shows structural similarities to the immunoglobulin superfamily. The CEA family consists of approximately 10 genes which are localized in two clusters on chromosome 19. So far, mRNA species for five of these genes have been identified which show tissue variability in their transcriptional activity. Expression of some of these genes in heterologous systems has been achieved, allowing the localization of some epitopes. The characterization of a CEA gene family in the rat and a comparison with its human counterpart has been utilized in the development of an evolutionary model.

p38/synaptophysin is a membrane protein present

in clear (synaptic) vesicles of neurons and endocrine

ceHs [1-4]. From the amino acid sequence

deduced from cDNAs encoding p38/synaptophysin,

a model with several membrane spanning

polypeptide segments and a carboxy-terminal

protein domain exposed to the cytoplasmic surface

has been constructed [5-7].

The function of p38/synaptophysin is not

known. It has been suggested to form a transmembrane

channel for ions, or to interact with

cytoplasmic factors via its cytoplasmic domain [7].

Since synaptophysin binds Ca2

+, it may also play

a role in the release of neurotransmitters stored in

clear (synaptic) vesicles [3].

Recently it has been reported [8] that p38/synaptophysin

also occurs in hormone containing large

dense core vesicles. This would imply that

p38/synaptophysin could fulfill similar functions

as described above in chromaffin and other

secretory ceHs containing large dense core vesicles.

In dear (synaptic) vesicles p38/synaptophysin constitutes

7.51Jfo of the vesicle membrane proteins [I].

The amount of p38/synaptophysin in large dense

core vesides is not known. Here we report on the

quantification of p38/synaptophysin in highly

purified chromaffin secretory vesides

We determined the cellular distribution and the amount of chromogranin A in endocrine cells of bovine pancreas using a polyclonal antibody against bovine adrenomedullary chromogranin A. The relative amounts of chromogranin A in the different cells of the endocrine pancreas were determined by computer-assisted analyses of the optical densities of the immunoreactivities in the stained sections. More than 80% of the immunoreactive chromogranin A was located in the pancreatic B-cells. In immunoblots of acid tissue extracts, only one chromogranin A band (MW 74 KD) was observed. Quantification of the immunoblots revealed that 3 micrograms of chromogranin A and 918 micrograms of insulin were present per gram pancreas (wet weight), equivalent to a molar ratio of 460 mumol chromogranin A per mol insulin.